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Is it possible to have life in vacuum?

Is it possible to have life in vacuum?


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I just got struck by curiosity now: Intuition says no, but I've never had confirmation of it.


As @terdon comments, dormant organisms can survive in vacuum. This includes lichens, bacteria, and even an animal: the ever-amazing and adorable tardigrade (Jönnson et al 2008). In 2006, tardigrades survived exposure to the vacuum of outer space with no appreciable difference in mortality compared to controls.

Tardigrade Hypsibius dujardini, a different genus than the ones sent into space, but probably equally hardy. Photo by Bob Goldstein & Vicky Madden (CC by-nc-ca via Goldstein lab - tardigrades on flickr).


Jönsson, K. I. et al (2008). Tardigrades survive exposure to space in low Earth orbit. Current Biology 18(17):R729-R731


No, it is not. Or at least not in the form we know life. The reason is that water (which is essential for life) boils at low pressures at room temperature. This makes life impossible in the form we live it on earth.


No, because some kind of fluid (liquid or gas) is necessary to supply resources and carry away wastes. Bacterial spores, tardigrades, etc. are in a dormant state when in a vacuum.


Extremophiles and Extreme Environments

Over the last decades, scientists have been intrigued by the fascinating organisms that inhabit extreme environments. Such organisms, known as extremophiles, thrive in habitats which for other terrestrial life-forms are intolerably hostile or even lethal. They thrive in extreme hot niches, ice, and salt solutions, as well as acid and alkaline conditions some may grow in toxic waste, organic solvents, heavy metals, or in several other habitats that were previously considered inhospitable for life. Extremophiles have been found depths of 6.7 km inside the Earth’s crust, more than 10 km deep inside the ocean𠅊t pressures of up to 110 MPa from extreme acid (pH 0) to extreme basic conditions (pH 12.8) and from hydrothermal vents at 122 ଌ to frozen sea water, at � ଌ. For every extreme environmental condition investigated, a variety of organisms have shown that they not only can tolerate these conditions, but that they also often require those conditions for survival.

They are classified according to the conditions in which they grow: As thermophiles and hyperthermophiles (organisms growing at high or very high temperatures, respectively), psychrophiles (organisms that grow best at low temperatures), acidophiles and alkaliphiles (organisms optimally adapted to acidic or basic pH values, respectively), barophiles (organisms that grow best under pressure), and halophiles (organisms that require NaCl for growth). In addition, these organisms are normally polyextremophiles, being adapted to live in habitats where various physicochemical parameters reach extreme values. For example, many hot springs are acid or alkaline at the same time, and usually rich in metal content the deep ocean is generally cold, oligotrophic (very low nutrient content), and exposed to high pressure and several hypersaline lakes are very alkaline.

Extremophiles may be divided into two broad categories: extremophilic organisms which require one or more extreme conditions in order to grow, and extremotolerant organisms which can tolerate extreme values of one or more physicochemical parameters though growing optimally at “normal” conditions.

Extremophiles include members of all three domains of life, i.e., bacteria, archaea, and eukarya. Most extremophiles are microorganisms (and a high proportion of these are archaea), but this group also includes eukaryotes such as protists (e.g., algae, fungi and protozoa) and multicellular organisms.

Archaea is the main group to thrive in extreme environments. Although members of this group are generally less versatile than bacteria and eukaryotes, they are generally quite skilled in adapting to different extreme conditions, holding frequently extremophily records. Some archaea are among the most hyperthermophilic, acidophilic, alkaliphilic, and halophilic microorganisms known. For example, the archaeal Methanopyrus kandleri strain 116 grows at 122 ଌ (252 ଏ, the highest recorded temperature), while the genus Picrophilus (e.g., Picrophilus torridus) include the most acidophilic organisms currently known, with the ability to grow at a pH of 0.06.

Among bacteria, the best adapted group to various extreme conditions is the cyanobacteria. They often form microbial mats with other bacteria, from Antarctic ice to continental hot springs. Cyanobacteria can also develop in hypersaline and alkaline lakes, support high metal concentrations and tolerate xerophilic conditions (i.e., low availability of water), forming endolithic communities in desertic regions. However, cyanobacteria are rarely found in acidic environments at pH values lower than 5𠄶.

Among eukaryotes, fungi (alone or in symbiosis with cyanobacteria or algae forming lichens) are the most versatile and ecologically successful phylogenetic lineage. With the exception of hyperthermophily, they adapt well to extreme environments. Fungi live in acidic and metal-enriched waters from mining regions, alkaline conditions, hot and cold deserts, the deep ocean and in hypersaline regions such as the Dead Sea. Nevertheless, in terms of high resistance to extreme conditions, one of the most impressive eukaryotic polyextremophiles is the tardigrade, a microscopic invertebrate. Tardigrades can go into a hibernation mode, called the tun state, whereby it can survive temperatures from � ଌ (1 ଌ above absolute zero!) to 151 ଌ, vacuum conditions (imposing extreme dehydration), pressure of 6,000 atm as well as exposure to X-rays and gamma-rays. Furthermore, even active tardigrades show tolerance to some extreme environments such as extreme low temperature and high doses of radiation.

In general, the phylogenetic diversity of extremophiles is high and very complex to study. Some orders or genera contain only extremophiles, whereas other orders or genera contain both extremophiles and non-extremophiles. Interestingly, extremophiles adapted to the same extreme condition may be broadly dispersed in the phylogenetic tree of life. This is the case for different psychrophiles or barophiles, for which members may be found dispersed in the three domains of life. There are also groups of organisms belonging to the same phylogenetic family that have adapted to very diverse extreme or moderately extreme conditions.

Over the last few decades, the fast development of molecular biology techniques has led to significant advances in the field, allowing us to investigate intriguing questions on the nature of extremophiles with unprecedented precision. In particular, new high-throughput DNA sequencing technologies have revolutionized how we explore extreme microbiology, revealing microbial ecosystems with unexpectedly high levels of diversity and complexity. Nevertheless, a thorough knowledge of the physiology of organisms in culture is essential to complement genomic or transcriptomic studies and cannot be replaced by any other approach. Consequently, the combination of improved traditional methods of isolation/cultivation and modern culture-independent techniques may be considered the best approach towards a better understanding of how microorganisms survive and function in such extreme environments.

Based on such technological advances, the study of extremophiles has provided, over the last few years, ground-breaking discoveries that challenge the paradigms of modern biology and make us rethink intriguing questions such as “what is life?”, “what are the limits of life?”, and “what are the fundamental features of life?”. These findings have made the study of life in extreme environments one of the most exciting areas of research, and can tell us much about the fundaments of life.

The mechanisms by which different organisms adapt to extreme environments provide a unique perspective on the fundamental characteristics of biological processes, such as the biochemical limits to macromolecular stability and the genetic instructions for constructing macromolecules that stabilize in one or more extreme conditions. These organisms present a wide and versatile metabolic diversity coupled with extraordinary physiological capacities to colonize extreme environments. In addition to the familiar metabolic pathway of photosynthesis, extremophiles possess metabolisms based upon methane, sulfur, and even iron.

Although the molecular strategies employed for survival in such environments are still not fully clarified, it is known that these organisms have adapted biomolecules and peculiar biochemical pathways which are of great interest for biotechnological purposes. Their stability and activity at extreme conditions make them useful alternatives to labile mesophilic molecules. This is particularly true for their enzymes, which remain catalytically active under extremes of temperature, salinity, pH, and solvent conditions. Interestingly, some of these enzymes display polyextremophilicity (i.e., stability and activity in more than one extreme condition) that make their wide use in industrial biotechnology possible.

From an evolutionary and phylogenetic perspective, an important achievement that has emerged from studies involving extremophiles is that some of these organisms form a cluster on the base of the tree of life. Many extremophiles, in particular the hyperthermophiles, lie close to the “universal ancestor” of all organisms on Earth. For this reason, extremophiles are critical for evolutionary studies related to the origins of life. It is also important to point out that the third domain of life, the archaea, was discovered partly due to the first studies on extremophiles, with profound consequences for evolutionary biology.

Furthermore, the study of extreme environments has become a key area of research for astrobiology. Understanding the biology of extremophiles and their ecosystems permits developing hypotheses regarding the conditions required for the origin and evolution of life elsewhere in the universe. Consequently, extremophiles may be considered as model organisms when exploring the existence of extraterrestrial life in planets and moons of the Solar System and beyond. For example, the microorganisms discovered in ice cores recovered from the depth of the Lake Vostok and other perennially subglacial lakes from Antarctica may serve as models for the search of life in the Jupiter’s moon Europa. Microbial ecosystems found in extreme environments like the Atacama Desert, the Antarctic Dry Valleys and the Rio Tinto may be analogous to potential life forms adapted to Martian conditions. Likewise, hyperthermophilic microorganisms present in hot springs, hydrothermal vents and other sites heated by volcanic activity in terrestrial or marine areas may resemble potential life forms existing in other extraterrestrial environments. Recently, the introduction of novel techniques such as Raman spectroscopy into the search of life signs using extremophilic organisms as models has open further perspectives that might be very useful in astrobiology.

With these groundbreaking discoveries and recent advances in the world of exthemophiles, which have profound implications for different branches of life sciences, our knowledge about the biosphere has grown and the putative boundaries of life have expanded. However, despite the latest advances we are just at the beginning of exploring and characterizing the world of extremophiles. This special issue discusses several aspects of these fascinating organisms, exploring their habitats, biodiversity, ecology, evolution, genetics, biochemistry, and biotechnological applications in a collection of exciting reviews and original articles written by leading experts and research groups in the field. I would like to thank the authors and co-authors for submitting such interesting contributions. I also thank the Editorial Office and numerous reviewers for their valuable assistance in reviewing the manuscripts.


You Can’t Always Believe Your Brain

If you’re like most people, your brain is filled with a constant chatter of thoughts, beliefs, and memories, which are mostly negative and from your childhood. This material is usually below your conscious awareness, cannot be directly measured or retrieved, and yet is very real and has a huge impact on your life and happiness.

In You Are Not Your Brain, Jeffrey Schwartz, M.D. and Rebecca Gladding, M.D. call these “deceptive brain messages” which they define as:

Any false or inaccurate thought or unhelpful or distracting impulse, urge, or desire that takes you away from your true goals and intentions in life.

Deceptive brain messages set up a vicious cycle which can take a devastating toll on people’s lives resulting in depression, anxiety, relationship problems, isolation, addictions, unhealthy habits, and more.

The cycle starts with a thought that causes you discomfort and takes you away from your goals and values. These thoughts are generated as part of your automatic mind, often referred to as negative self-talk or inner-critic, and are made up of implicit memories and learned beliefs from your past. Some common deceptive brain messages are:

  • I should have/shouldn’t have…
  • I’m a bad person.
  • I don’t deserve to be happy.
  • I’m not good enough.
  • I can’t do this/make it…..
  • I want to escape.

The thought might be accompanied by a physical sensation or an emotional state. For example:

  • Pounding heart
  • Butterflies
  • Sweating
  • Anxiety
  • Feeling hopeless/helpless
  • Having a craving for something or urge to act

In an effort to ease the unpleasant sensation or emotion, you typically behave in automatic, habitual ways. In many cases, you may not even be consciously aware of your response or the motives behind it. Some habitual responses might include:

  • Using drugs or alcohol
  • Eating/dieting/purging
  • Shopping/spending money/gambling
  • Compulsive sex
  • Avoidance behaviors
  • Repeatedly checking something (email, texts, door locks)
  • Overthinking or worrying

The authors make the distinction between emotions and emotional sensations and stress the importance of knowing the difference. For their purposes, an emotion is based on a real event in proportional to the happening and shouldn’t be avoided, but experienced and constructively processed. An emotional sensation is a feeling based on a deceptive brain message and leads you to act in unhealthy ways. It’s like the difference between feeling sad because your pet died and feeling sad because you feel unlovable and like no one cares about you. (See blog: What’s The Difference Between Feelings And Emotions)


Contents

The definition of life has long been a challenge for scientists and philosophers, with many varied definitions put forward. [16] [17] [18] This is partially because life is a process, not a substance. [19] [20] [21] This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside of Earth. [22] [23] Philosophical definitions of life have also been put forward, with similar difficulties on how to distinguish living things from the non-living. [24] Legal definitions of life have also been described and debated, though these generally focus on the decision to declare a human dead, and the legal ramifications of this decision. [25] As many as 123 definitions of life have been compiled. [26] One definition seems to be favored by NASA: “a self-sustaining chemical system capable of Darwinian evolution.” [27] [28] [29] [30] More simply, life is, "matter that can reproduce itself and evolve as survival dictates". [31] [32] [33]

Biology

Since there is no unequivocal definition of life, most current definitions in biology are descriptive. Life is considered a characteristic of something that preserves, furthers or reinforces its existence in the given environment. This characteristic exhibits all or most of the following traits: [18] [34] [35] [36] [37] [38] [39]

  1. Homeostasis: regulation of the internal environment to maintain a constant state for example, sweating to reduce temperature
  2. Organization: being structurally composed of one or more cells – the basic units of life
  3. Metabolism: transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
  4. Growth: maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.
  5. Adaptation: the ability to change over time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity, diet, and external factors.
  6. Response to stimuli: a response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion for example, the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
  7. Reproduction: the ability to produce new individual organisms, either asexually from a single parent organism or sexually from two parent organisms.

These complex processes, called physiological functions, have underlying physical and chemical bases, as well as signaling and control mechanisms that are essential to maintaining life.

Alternative definitions

From a physics perspective, living beings are thermodynamic systems with an organized molecular structure that can reproduce itself and evolve as survival dictates. [40] [41] Thermodynamically, life has been described as an open system which makes use of gradients in its surroundings to create imperfect copies of itself. [42] Another way of putting this is to define life as "a self-sustained chemical system capable of undergoing Darwinian evolution", a definition adopted by a NASA committee attempting to define life for the purposes of exobiology, based on a suggestion by Carl Sagan. [43] [44] [45] A major strength of this definition is that it distinguishes life by the evolutionary process rather than its chemical composition. [46]

Others take a systemic viewpoint that does not necessarily depend on molecular chemistry. One systemic definition of life is that living things are self-organizing and autopoietic (self-producing). Variations of this definition include Stuart Kauffman's definition as an autonomous agent or a multi-agent system capable of reproducing itself or themselves, and of completing at least one thermodynamic work cycle. [47] This definition is extended by the apparition of novel functions over time. [48]

Viruses

Whether or not viruses should be considered as alive is controversial. They are most often considered as just gene coding replicators rather than forms of life. [49] They have been described as "organisms at the edge of life" [50] because they possess genes, evolve by natural selection, [51] [52] and replicate by creating multiple copies of themselves through self-assembly. However, viruses do not metabolize and they require a host cell to make new products. Virus self-assembly within host cells has implications for the study of the origin of life, as it may support the hypothesis that life could have started as self-assembling organic molecules. [53] [54] [55]

Biophysics

To reflect the minimum phenomena required, other biological definitions of life have been proposed, [56] with many of these being based upon chemical systems. Biophysicists have commented that living things function on negative entropy. [57] [58] In other words, living processes can be viewed as a delay of the spontaneous diffusion or dispersion of the internal energy of biological molecules towards more potential microstates. [16] In more detail, according to physicists such as John Bernal, Erwin Schrödinger, Eugene Wigner, and John Avery, life is a member of the class of phenomena that are open or continuous systems able to decrease their internal entropy at the expense of substances or free energy taken in from the environment and subsequently rejected in a degraded form. [59] [60] The emergence and increasing popularity of biomimetics or biomimicry (the design and production of materials, structures, and systems that are modeled on biological entities and processes) will likely redefine the boundary between natural and artificial life. [61]

Living systems theories

Living systems are open self-organizing living things that interact with their environment. These systems are maintained by flows of information, energy, and matter.

Budisa, Kubyshkin and Schmidt defined cellular life as an organizational unit resting on four pillars/cornerstones: (i) energy, (ii) metabolism, (iii) information and (iv) form. This system is able to regulate and control metabolism and energy supply and contains at least one subsystem that functions as an information carrier (genetic information). Cells as self-sustaining units are parts of different populations that are involved in the unidirectional and irreversible open-ended process known as evolution. [62]

Some scientists have proposed in the last few decades that a general living systems theory is required to explain the nature of life. [63] Such a general theory would arise out of the ecological and biological sciences and attempt to map general principles for how all living systems work. Instead of examining phenomena by attempting to break things down into components, a general living systems theory explores phenomena in terms of dynamic patterns of the relationships of organisms with their environment. [64]

Gaia hypothesis

The idea that the Earth is alive is found in philosophy and religion, but the first scientific discussion of it was by the Scottish scientist James Hutton. In 1785, he stated that the Earth was a superorganism and that its proper study should be physiology. Hutton is considered the father of geology, but his idea of a living Earth was forgotten in the intense reductionism of the 19th century. [65] : 10 The Gaia hypothesis, proposed in the 1960s by scientist James Lovelock, [66] [67] suggests that life on Earth functions as a single organism that defines and maintains environmental conditions necessary for its survival. [65] This hypothesis served as one of the foundations of the modern Earth system science.

Nonfractionability

Robert Rosen devoted a large part of his career, from 1958 [68] onwards, to developing a comprehensive theory of life as a self-organizing complex system, "closed to efficient causation" [69] He defined a system component as "a unit of organization a part with a function, i.e., a definite relation between part and whole." He identified the "nonfractionability of components in an organism" as the fundamental difference between living systems and "biological machines." He summarized his views in his book Life Itself. [70] Similar ideas may be found in the book Living Systems [71] by James Grier Miller.

Life as a property of ecosystems

A systems view of life treats environmental fluxes and biological fluxes together as a "reciprocity of influence," [72] and a reciprocal relation with environment is arguably as important for understanding life as it is for understanding ecosystems. As Harold J. Morowitz (1992) explains it, life is a property of an ecological system rather than a single organism or species. [73] He argues that an ecosystemic definition of life is preferable to a strictly biochemical or physical one. Robert Ulanowicz (2009) highlights mutualism as the key to understand the systemic, order-generating behavior of life and ecosystems. [74]

Complex systems biology

Complex systems biology (CSB) is a field of science that studies the emergence of complexity in functional organisms from the viewpoint of dynamic systems theory. [75] The latter is also often called systems biology and aims to understand the most fundamental aspects of life. A closely related approach to CSB and systems biology called relational biology is concerned mainly with understanding life processes in terms of the most important relations, and categories of such relations among the essential functional components of organisms for multicellular organisms, this has been defined as "categorical biology", or a model representation of organisms as a category theory of biological relations, as well as an algebraic topology of the functional organization of living organisms in terms of their dynamic, complex networks of metabolic, genetic, and epigenetic processes and signaling pathways. [76] [77] Alternative but closely related approaches focus on the interdependance of constraints, where constraints can be either molecular, such as enzymes, or macroscopic, such as the geometry of a bone or of the vascular system. [78]

Darwinian dynamic

It has also been argued that the evolution of order in living systems and certain physical systems obeys a common fundamental principle termed the Darwinian dynamic. [79] [80] The Darwinian dynamic was formulated by first considering how macroscopic order is generated in a simple non-biological system far from thermodynamic equilibrium, and then extending consideration to short, replicating RNA molecules. The underlying order-generating process was concluded to be basically similar for both types of systems. [79]

Operator theory

Another systemic definition called the operator theory proposes that "life is a general term for the presence of the typical closures found in organisms the typical closures are a membrane and an autocatalytic set in the cell" [81] and that an organism is any system with an organisation that complies with an operator type that is at least as complex as the cell. [82] [83] [84] [85] Life can also be modeled as a network of inferior negative feedbacks of regulatory mechanisms subordinated to a superior positive feedback formed by the potential of expansion and reproduction. [86]

Materialism

Some of the earliest theories of life were materialist, holding that all that exists is matter, and that life is merely a complex form or arrangement of matter. Empedocles (430 BC) argued that everything in the universe is made up of a combination of four eternal "elements" or "roots of all": earth, water, air, and fire. All change is explained by the arrangement and rearrangement of these four elements. The various forms of life are caused by an appropriate mixture of elements. [87]

Democritus (460 BC) thought that the essential characteristic of life is having a soul (psyche). Like other ancient writers, he was attempting to explain what makes something a living thing. His explanation was that fiery atoms make a soul in exactly the same way atoms and void account for any other thing. He elaborates on fire because of the apparent connection between life and heat, and because fire moves. [88]

Plato's world of eternal and unchanging Forms, imperfectly represented in matter by a divine Artisan, contrasts sharply with the various mechanistic Weltanschauungen, of which atomism was, by the fourth century at least, the most prominent . This debate persisted throughout the ancient world. Atomistic mechanism got a shot in the arm from Epicurus . while the Stoics adopted a divine teleology . The choice seems simple: either show how a structured, regular world could arise out of undirected processes, or inject intelligence into the system. [89]

The mechanistic materialism that originated in ancient Greece was revived and revised by the French philosopher René Descartes (1596–1650), who held that animals and humans were assemblages of parts that together functioned as a machine. This idea was developed further by Julien Offray de La Mettrie (1709–1750) in his book L'Homme Machine. [90]

In the 19th century, the advances in cell theory in biological science encouraged this view. The evolutionary theory of Charles Darwin (1859) is a mechanistic explanation for the origin of species by means of natural selection. [91]

At the beginning of the 20th century Stéphane Leduc (1853–1939) promoted the idea that biological processes could be understood in terms of physics and chemistry, and that their growth resembled that of inorganic crystals immersed in solutions of sodium silicate. His ideas, set out in his book La biologie synthétique [92] was widely dismissed during his lifetime, but has incurred a resurgence of interest in the work of Russell, Barge and colleagues. [93]

Hylomorphism

Hylomorphism is a theory first expressed by the Greek philosopher Aristotle (322 BC). The application of hylomorphism to biology was important to Aristotle, and biology is extensively covered in his extant writings. In this view, everything in the material universe has both matter and form, and the form of a living thing is its soul (Greek psyche, Latin anima). There are three kinds of souls: the vegetative soul of plants, which causes them to grow and decay and nourish themselves, but does not cause motion and sensation the animal soul, which causes animals to move and feel and the rational soul, which is the source of consciousness and reasoning, which (Aristotle believed) is found only in man. [94] Each higher soul has all of the attributes of the lower ones. Aristotle believed that while matter can exist without form, form cannot exist without matter, and that therefore the soul cannot exist without the body. [95]

This account is consistent with teleological explanations of life, which account for phenomena in terms of purpose or goal-directedness. Thus, the whiteness of the polar bear's coat is explained by its purpose of camouflage. The direction of causality (from the future to the past) is in contradiction with the scientific evidence for natural selection, which explains the consequence in terms of a prior cause. Biological features are explained not by looking at future optimal results, but by looking at the past evolutionary history of a species, which led to the natural selection of the features in question. [96]

Spontaneous generation

Spontaneous generation was the belief that living organisms can form without descent from similar organisms. Typically, the idea was that certain forms such as fleas could arise from inanimate matter such as dust or the supposed seasonal generation of mice and insects from mud or garbage. [97]

The theory of spontaneous generation was proposed by Aristotle, [98] who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms it held sway for two millennia. It was decisively dispelled by the experiments of Louis Pasteur in 1859, who expanded upon the investigations of predecessors such as Francesco Redi. [99] [100] Disproof of the traditional ideas of spontaneous generation is no longer controversial among biologists. [101] [102] [103]

Vitalism

Vitalism is the belief that the life-principle is non-material. This originated with Georg Ernst Stahl (17th century), and remained popular until the middle of the 19th century. It appealed to philosophers such as Henri Bergson, Friedrich Nietzsche, and Wilhelm Dilthey, [104] anatomists like Xavier Bichat, and chemists like Justus von Liebig. [105] Vitalism included the idea that there was a fundamental difference between organic and inorganic material, and the belief that organic material can only be derived from living things. This was disproved in 1828, when Friedrich Wöhler prepared urea from inorganic materials. [106] This Wöhler synthesis is considered the starting point of modern organic chemistry. It is of historical significance because for the first time an organic compound was produced in inorganic reactions. [105]

During the 1850s, Hermann von Helmholtz, anticipated by Julius Robert von Mayer, demonstrated that no energy is lost in muscle movement, suggesting that there were no "vital forces" necessary to move a muscle. [107] These results led to the abandonment of scientific interest in vitalistic theories, especially after Buchner's demonstration that alcoholic fermentation could occur in cell-free extracts of yeast. [108] Nonetheless, the belief still exists in pseudoscientific theories such as homeopathy, which interprets diseases and sickness as caused by disturbances in a hypothetical vital force or life force. [109]

The age of the Earth is about 4.54 billion years. [110] [111] [112] Evidence suggests that life on Earth has existed for at least 3.5 billion years, [113] [114] [115] [116] [117] [118] [119] [120] [121] with the oldest physical traces of life dating back 3.7 billion years [122] [123] [124] however, some theories, such as the Late Heavy Bombardment theory, suggest that life on Earth may have started even earlier, as early as 4.1–4.4 billion years ago, [113] [114] [115] [116] [117] and the chemistry leading to life may have begun shortly after the Big Bang, 13.8 billion years ago, during an epoch when the universe was only 10–17 million years old. [125] [126] [127]

More than 99% of all species of life forms, amounting to over five billion species, [128] that ever lived on Earth are estimated to be extinct. [129] [130]

Although the number of Earth's catalogued species of lifeforms is between 1.2 million and 2 million, [131] [132] the total number of species in the planet is uncertain. Estimates range from 8 million to 100 million, [131] [132] with a more narrow range between 10 and 14 million, [131] but it may be as high as 1 trillion (with only one-thousandth of one percent of the species described) according to studies realized in May 2016. [133] [134] The total number of related DNA base pairs on Earth is estimated at 5.0 x 10 37 and weighs 50 billion tonnes. [135] In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon). [136] In July 2016, scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor (LUCA) of all organisms living on Earth. [137]

All known life forms share fundamental molecular mechanisms, reflecting their common descent based on these observations, hypotheses on the origin of life attempt to find a mechanism explaining the formation of a universal common ancestor, from simple organic molecules via pre-cellular life to protocells and metabolism. Models have been divided into "genes-first" and "metabolism-first" categories, but a recent trend is the emergence of hybrid models that combine both categories. [138]

There is no current scientific consensus as to how life originated. However, most accepted scientific models build on the Miller–Urey experiment and the work of Sidney Fox, which show that conditions on the primitive Earth favored chemical reactions that synthesize amino acids and other organic compounds from inorganic precursors, [139] and phospholipids spontaneously form lipid bilayers, the basic structure of a cell membrane.

Living organisms synthesize proteins, which are polymers of amino acids using instructions encoded by deoxyribonucleic acid (DNA). Protein synthesis entails intermediary ribonucleic acid (RNA) polymers. One possibility for how life began is that genes originated first, followed by proteins [140] the alternative being that proteins came first and then genes. [141]

However, because genes and proteins are both required to produce the other, the problem of considering which came first is like that of the chicken or the egg. Most scientists have adopted the hypothesis that because of this, it is unlikely that genes and proteins arose independently. [142]

Therefore, a possibility, first suggested by Francis Crick, [143] is that the first life was based on RNA, [142] which has the DNA-like properties of information storage and the catalytic properties of some proteins. This is called the RNA world hypothesis, and it is supported by the observation that many of the most critical components of cells (those that evolve the slowest) are composed mostly or entirely of RNA. Also, many critical cofactors (ATP, Acetyl-CoA, NADH, etc.) are either nucleotides or substances clearly related to them. The catalytic properties of RNA had not yet been demonstrated when the hypothesis was first proposed, [144] but they were confirmed by Thomas Cech in 1986. [145]

One issue with the RNA world hypothesis is that synthesis of RNA from simple inorganic precursors is more difficult than for other organic molecules. One reason for this is that RNA precursors are very stable and react with each other very slowly under ambient conditions, and it has also been proposed that living organisms consisted of other molecules before RNA. [146] However, the successful synthesis of certain RNA molecules under the conditions that existed prior to life on Earth has been achieved by adding alternative precursors in a specified order with the precursor phosphate present throughout the reaction. [147] This study makes the RNA world hypothesis more plausible. [148]

Geological findings in 2013 showed that reactive phosphorus species (like phosphite) were in abundance in the ocean before 3.5 Ga, and that Schreibersite easily reacts with aqueous glycerol to generate phosphite and glycerol 3-phosphate. [149] It is hypothesized that Schreibersite-containing meteorites from the Late Heavy Bombardment could have provided early reduced phosphorus, which could react with prebiotic organic molecules to form phosphorylated biomolecules, like RNA. [149]

In 2009, experiments demonstrated Darwinian evolution of a two-component system of RNA enzymes (ribozymes) in vitro. [150] The work was performed in the laboratory of Gerald Joyce, who stated "This is the first example, outside of biology, of evolutionary adaptation in a molecular genetic system." [151]

Prebiotic compounds may have originated extraterrestrially. NASA findings in 2011, based on studies with meteorites found on Earth, suggest DNA and RNA components (adenine, guanine and related organic molecules) may be formed in outer space. [152] [153] [154] [155]

In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine and thymine, have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), the most carbon-rich chemical found in the universe, may have been formed in red giants or in interstellar dust and gas clouds, according to the scientists. [156]

According to the panspermia hypothesis, microscopic life—distributed by meteoroids, asteroids and other small Solar System bodies—may exist throughout the universe. [157] [158]

The diversity of life on Earth is a result of the dynamic interplay between genetic opportunity, metabolic capability, environmental challenges, [159] and symbiosis. [160] [161] [162] For most of its existence, Earth's habitable environment has been dominated by microorganisms and subjected to their metabolism and evolution. As a consequence of these microbial activities, the physical-chemical environment on Earth has been changing on a geologic time scale, thereby affecting the path of evolution of subsequent life. [159] For example, the release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced global changes in the Earth's environment. Because oxygen was toxic to most life on Earth at the time, this posed novel evolutionary challenges, and ultimately resulted in the formation of Earth's major animal and plant species. This interplay between organisms and their environment is an inherent feature of living systems. [159]

Biosphere

The biosphere is the global sum of all ecosystems. It can also be termed as the zone of life on Earth, a closed system (apart from solar and cosmic radiation and heat from the interior of the Earth), and largely self-regulating. [163] By the most general biophysiological definition, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, geosphere, hydrosphere, and atmosphere.

Life forms live in every part of the Earth's biosphere, including soil, hot springs, inside rocks at least 19 km (12 mi) deep underground, the deepest parts of the ocean, and at least 64 km (40 mi) high in the atmosphere. [164] [165] [166] Under certain test conditions, life forms have been observed to thrive in the near-weightlessness of space [167] [168] and to survive in the vacuum of outer space. [169] [170] Life forms appear to thrive in the Mariana Trench, the deepest spot in the Earth's oceans. [171] [172] Other researchers reported related studies that life forms thrive inside rocks up to 580 m (1,900 ft 0.36 mi) below the sea floor under 2,590 m (8,500 ft 1.61 mi) of ocean off the coast of the northwestern United States, [171] [173] as well as 2,400 m (7,900 ft 1.5 mi) beneath the seabed off Japan. [174] In August 2014, scientists confirmed the existence of life forms living 800 m (2,600 ft 0.50 mi) below the ice of Antarctica. [175] [176] According to one researcher, "You can find microbes everywhere—they're extremely adaptable to conditions, and survive wherever they are." [171]

The biosphere is postulated to have evolved, beginning with a process of biopoesis (life created naturally from non-living matter, such as simple organic compounds) or biogenesis (life created from living matter), at least some 3.5 billion years ago. [177] [178] The earliest evidence for life on Earth includes biogenic graphite found in 3.7 billion-year-old metasedimentary rocks from Western Greenland [122] and microbial mat fossils found in 3.48 billion-year-old sandstone from Western Australia. [123] [124] More recently, in 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia. [114] [115] In 2017, putative fossilized microorganisms (or microfossils) were announced to have been discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada that were as old as 4.28 billion years, the oldest record of life on earth, suggesting "an almost instantaneous emergence of life" after ocean formation 4.4 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. [1] [2] [3] [4] According to biologist Stephen Blair Hedges, "If life arose relatively quickly on Earth . then it could be common in the universe." [114]

In a general sense, biospheres are any closed, self-regulating systems containing ecosystems. This includes artificial biospheres such as Biosphere 2 and BIOS-3, and potentially ones on other planets or moons. [179]

Range of tolerance

The inert components of an ecosystem are the physical and chemical factors necessary for life—energy (sunlight or chemical energy), water, heat, atmosphere, gravity, nutrients, and ultraviolet solar radiation protection. [180] In most ecosystems, the conditions vary during the day and from one season to the next. To live in most ecosystems, then, organisms must be able to survive a range of conditions, called the "range of tolerance." [181] Outside that are the "zones of physiological stress," where the survival and reproduction are possible but not optimal. Beyond these zones are the "zones of intolerance," where survival and reproduction of that organism is unlikely or impossible. Organisms that have a wide range of tolerance are more widely distributed than organisms with a narrow range of tolerance. [181]

Extremophiles

To survive, selected microorganisms can assume forms that enable them to withstand freezing, complete desiccation, starvation, high levels of radiation exposure, and other physical or chemical challenges. These microorganisms may survive exposure to such conditions for weeks, months, years, or even centuries. [159] Extremophiles are microbial life forms that thrive outside the ranges where life is commonly found. [182] They excel at exploiting uncommon sources of energy. While all organisms are composed of nearly identical molecules, evolution has enabled such microbes to cope with this wide range of physical and chemical conditions. Characterization of the structure and metabolic diversity of microbial communities in such extreme environments is ongoing. [183]

Microbial life forms thrive even in the Mariana Trench, the deepest spot in the Earth's oceans. [171] [172] Microbes also thrive inside rocks up to 1,900 feet (580 m) below the sea floor under 8,500 feet (2,600 m) of ocean. [171] [173] Expeditions of the International Ocean Discovery Program found unicellular life in 120°C sediment that is 1.2 km below seafloor in the Nankai Trough subduction zone. [184]

Investigation of the tenacity and versatility of life on Earth, [182] as well as an understanding of the molecular systems that some organisms utilize to survive such extremes, is important for the search for life beyond Earth. [159] For example, lichen could survive for a month in a simulated Martian environment. [185] [186]

Chemical elements

All life forms require certain core chemical elements needed for biochemical functioning. These include carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—the elemental macronutrients for all organisms [187] —often represented by the acronym CHNOPS. Together these make up nucleic acids, proteins and lipids, the bulk of living matter. Five of these six elements comprise the chemical components of DNA, the exception being sulfur. The latter is a component of the amino acids cysteine and methionine. The most biologically abundant of these elements is carbon, which has the desirable attribute of forming multiple, stable covalent bonds. This allows carbon-based (organic) molecules to form an immense variety of chemical arrangements. [188] Alternative hypothetical types of biochemistry have been proposed that eliminate one or more of these elements, swap out an element for one not on the list, or change required chiralities or other chemical properties. [189] [190]

Deoxyribonucleic acid is a molecule that carries most of the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. DNA and RNA are nucleic acids alongside proteins and complex carbohydrates, they are one of the three major types of macromolecule that are essential for all known forms of life. Most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix. The two DNA strands are known as polynucleotides since they are composed of simpler units called nucleotides. [191] Each nucleotide is composed of a nitrogen-containing nucleobase—either cytosine (C), guanine (G), adenine (A), or thymine (T)—as well as a sugar called deoxyribose and a phosphate group. The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. According to base pairing rules (A with T, and C with G), hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 10 37 , and weighs 50 billion tonnes. [135] In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon). [136]

DNA stores biological information. The DNA backbone is resistant to cleavage, and both strands of the double-stranded structure store the same biological information. Biological information is replicated as the two strands are separated. A significant portion of DNA (more than 98% for humans) is non-coding, meaning that these sections do not serve as patterns for protein sequences.

The two strands of DNA run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of nucleobases (informally, bases). It is the sequence of these four nucleobases along the backbone that encodes biological information. Under the genetic code, RNA strands are translated to specify the sequence of amino acids within proteins. These RNA strands are initially created using DNA strands as a template in a process called transcription.

Within cells, DNA is organized into long structures called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, providing each cell its own complete set of chromosomes. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. [192] In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.

DNA was first isolated by Friedrich Miescher in 1869. [193] Its molecular structure was identified by James Watson and Francis Crick in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Rosalind Franklin. [194]

Antiquity

The first known attempt to classify organisms was conducted by the Greek philosopher Aristotle (384–322 BC), who classified all living organisms known at that time as either a plant or an animal, based mainly on their ability to move. He also distinguished animals with blood from animals without blood (or at least without red blood), which can be compared with the concepts of vertebrates and invertebrates respectively, and divided the blooded animals into five groups: viviparous quadrupeds (mammals), oviparous quadrupeds (reptiles and amphibians), birds, fishes and whales. The bloodless animals were also divided into five groups: cephalopods, crustaceans, insects (which included the spiders, scorpions, and centipedes, in addition to what we define as insects today), shelled animals (such as most molluscs and echinoderms), and "zoophytes" (animals that resemble plants). Though Aristotle's work in zoology was not without errors, it was the grandest biological synthesis of the time and remained the ultimate authority for many centuries after his death. [195]

Linnaean

The exploration of the Americas revealed large numbers of new plants and animals that needed descriptions and classification. In the latter part of the 16th century and the beginning of the 17th, careful study of animals commenced and was gradually extended until it formed a sufficient body of knowledge to serve as an anatomical basis for classification.

In the late 1740s, Carl Linnaeus introduced his system of binomial nomenclature for the classification of species. Linnaeus attempted to improve the composition and reduce the length of the previously used many-worded names by abolishing unnecessary rhetoric, introducing new descriptive terms and precisely defining their meaning. [196] The Linnaean classification has eight levels: domains, kingdoms, phyla, class, order, family, genus, and species.

The fungi were originally treated as plants. For a short period Linnaeus had classified them in the taxon Vermes in Animalia, but later placed them back in Plantae. Copeland classified the Fungi in his Protoctista, thus partially avoiding the problem but acknowledging their special status. [197] The problem was eventually solved by Whittaker, when he gave them their own kingdom in his five-kingdom system. Evolutionary history shows that the fungi are more closely related to animals than to plants. [198]

As new discoveries enabled detailed study of cells and microorganisms, new groups of life were revealed, and the fields of cell biology and microbiology were created. These new organisms were originally described separately in protozoa as animals and protophyta/thallophyta as plants, but were united by Haeckel in the kingdom Protista later, the prokaryotes were split off in the kingdom Monera, which would eventually be divided into two separate groups, the Bacteria and the Archaea. This led to the six-kingdom system and eventually to the current three-domain system, which is based on evolutionary relationships. [199] However, the classification of eukaryotes, especially of protists, is still controversial. [200]

As microbiology, molecular biology and virology developed, non-cellular reproducing agents were discovered, such as viruses and viroids. Whether these are considered alive has been a matter of debate viruses lack characteristics of life such as cell membranes, metabolism and the ability to grow or respond to their environments. Viruses can still be classed into "species" based on their biology and genetics, but many aspects of such a classification remain controversial. [201]

In May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. [133]

The original Linnaean system has been modified over time as follows:

Linnaeus
1735 [202]
Haeckel
1866 [203]
Chatton
1925 [204]
Copeland
1938 [205]
Whittaker
1969 [206]
Woese et al.
1990 [199]
Cavalier-Smith
1998 [207]
Cavalier-Smith
2015 [208]
2 kingdoms 3 kingdoms 2 empires 4 kingdoms 5 kingdoms 3 domains 2 empires, 6 kingdoms 2 empires, 7 kingdoms
(not treated) Protista Prokaryota Monera Monera Bacteria Bacteria Bacteria
Archaea Archaea
Eukaryota Protoctista Protista Eucarya Protozoa Protozoa
Chromista Chromista
Vegetabilia Plantae Plantae Plantae Plantae Plantae
Fungi Fungi Fungi
Animalia Animalia Animalia Animalia Animalia Animalia

Cladistic

In the 1960s cladistics emerged: a system arranging taxa based on clades in an evolutionary or phylogenetic tree. [209]

Cells are the basic unit of structure in every living thing, and all cells arise from pre-existing cells by division. Cell theory was formulated by Henri Dutrochet, Theodor Schwann, Rudolf Virchow and others during the early nineteenth century, and subsequently became widely accepted. [210] The activity of an organism depends on the total activity of its cells, with energy flow occurring within and between them. Cells contain hereditary information that is carried forward as a genetic code during cell division. [211]

There are two primary types of cells. Prokaryotes lack a nucleus and other membrane-bound organelles, although they have circular DNA and ribosomes. Bacteria and Archaea are two domains of prokaryotes. The other primary type of cells are the eukaryotes, which have distinct nuclei bound by a nuclear membrane and membrane-bound organelles, including mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, and vacuoles. In addition, they possess organized chromosomes that store genetic material. All species of large complex organisms are eukaryotes, including animals, plants and fungi, though most species of eukaryote are protist microorganisms. [212] The conventional model is that eukaryotes evolved from prokaryotes, with the main organelles of the eukaryotes forming through endosymbiosis between bacteria and the progenitor eukaryotic cell. [213]

The molecular mechanisms of cell biology are based on proteins. Most of these are synthesized by the ribosomes through an enzyme-catalyzed process called protein biosynthesis. A sequence of amino acids is assembled and joined together based upon gene expression of the cell's nucleic acid. [214] In eukaryotic cells, these proteins may then be transported and processed through the Golgi apparatus in preparation for dispatch to their destination. [215]

Cells reproduce through a process of cell division in which the parent cell divides into two or more daughter cells. For prokaryotes, cell division occurs through a process of fission in which the DNA is replicated, then the two copies are attached to parts of the cell membrane. In eukaryotes, a more complex process of mitosis is followed. However, the end result is the same the resulting cell copies are identical to each other and to the original cell (except for mutations), and both are capable of further division following an interphase period. [216]

Multicellular organisms may have first evolved through the formation of colonies of identical cells. These cells can form group organisms through cell adhesion. The individual members of a colony are capable of surviving on their own, whereas the members of a true multi-cellular organism have developed specializations, making them dependent on the remainder of the organism for survival. Such organisms are formed clonally or from a single germ cell that is capable of forming the various specialized cells that form the adult organism. This specialization allows multicellular organisms to exploit resources more efficiently than single cells. [217] In January 2016, scientists reported that, about 800 million years ago, a minor genetic change in a single molecule, called GK-PID, may have allowed organisms to go from a single cell organism to one of many cells. [218]

Cells have evolved methods to perceive and respond to their microenvironment, thereby enhancing their adaptability. Cell signaling coordinates cellular activities, and hence governs the basic functions of multicellular organisms. Signaling between cells can occur through direct cell contact using juxtacrine signalling, or indirectly through the exchange of agents as in the endocrine system. In more complex organisms, coordination of activities can occur through a dedicated nervous system. [219]

Though life is confirmed only on Earth, many think that extraterrestrial life is not only plausible, but probable or inevitable. [220] [221] Other planets and moons in the Solar System and other planetary systems are being examined for evidence of having once supported simple life, and projects such as SETI are trying to detect radio transmissions from possible alien civilizations. Other locations within the Solar System that may host microbial life include the subsurface of Mars, the upper atmosphere of Venus, [222] and subsurface oceans on some of the moons of the giant planets. [223] [224] Beyond the Solar System, the region around another main-sequence star that could support Earth-like life on an Earth-like planet is known as the habitable zone. The inner and outer radii of this zone vary with the luminosity of the star, as does the time interval during which the zone survives. Stars more massive than the Sun have a larger habitable zone, but remain on the Sun-like "main sequence" of stellar evolution for a shorter time interval. Small red dwarfs have the opposite problem, with a smaller habitable zone that is subject to higher levels of magnetic activity and the effects of tidal locking from close orbits. Hence, stars in the intermediate mass range such as the Sun may have a greater likelihood for Earth-like life to develop. [225] The location of the star within a galaxy may also affect the likelihood of life forming. Stars in regions with a greater abundance of heavier elements that can form planets, in combination with a low rate of potentially habitat-damaging supernova events, are predicted to have a higher probability of hosting planets with complex life. [226] The variables of the Drake equation are used to discuss the conditions in planetary systems where civilization is most likely to exist. [227] Use of the equation to predict the amount of extraterrestrial life, however, is difficult because many of the variables are unknown, the equation functions as more of a mirror to what its user already thinks. As a result, the number of civilizations in the galaxy can be estimated as low as 9.1 x 10 −13 , suggesting a minimum value of 1, or as high as 15.6 million (0.156 x 10 9 ) for the calculations, see Drake equation.

Artificial life is the simulation of any aspect of life, as through computers, robotics, or biochemistry. [228] The study of artificial life imitates traditional biology by recreating some aspects of biological phenomena. Scientists study the logic of living systems by creating artificial environments—seeking to understand the complex information processing that defines such systems. While life is, by definition, alive, artificial life is generally referred to as data confined to a digital environment and existence.

Synthetic biology is a new area of biotechnology that combines science and biological engineering. The common goal is the design and construction of new biological functions and systems not found in nature. Synthetic biology includes the broad redefinition and expansion of biotechnology, with the ultimate goals of being able to design and build engineered biological systems that process information, manipulate chemicals, fabricate materials and structures, produce energy, provide food, and maintain and enhance human health and the environment. [229]

Death is the permanent termination of all vital functions or life processes in an organism or cell. [230] [231] It can occur as a result of an accident, medical conditions, biological interaction, malnutrition, poisoning, senescence, or suicide. After death, the remains of an organism re-enter the biogeochemical cycle. Organisms may be consumed by a predator or a scavenger and leftover organic material may then be further decomposed by detritivores, organisms that recycle detritus, returning it to the environment for reuse in the food chain.

One of the challenges in defining death is in distinguishing it from life. Death would seem to refer to either the moment life ends, or when the state that follows life begins. [231] However, determining when death has occurred is difficult, as cessation of life functions is often not simultaneous across organ systems. [232] Such determination therefore requires drawing conceptual lines between life and death. This is problematic, however, because there is little consensus over how to define life. The nature of death has for millennia been a central concern of the world's religious traditions and of philosophical inquiry. Many religions maintain faith in either a kind of afterlife or reincarnation for the soul, or resurrection of the body at a later date.

Extinction

Extinction is the process by which a group of taxa or species dies out, reducing biodiversity. [233] The moment of extinction is generally considered the death of the last individual of that species. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively after a period of apparent absence. Species become extinct when they are no longer able to survive in changing habitat or against superior competition. In Earth's history, over 99% of all the species that have ever lived are extinct [234] [128] [129] [130] however, mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. [235]

Fossils

Fossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossil-containing rock formations and sedimentary layers (strata) is known as the fossil record. A preserved specimen is called a fossil if it is older than the arbitrary date of 10,000 years ago. [236] Hence, fossils range in age from the youngest at the start of the Holocene Epoch to the oldest from the Archaean Eon, up to 3.4 billion years old. [237] [238]


Myth number three: Power is strategically acquired, not given

A major reason why Machiavellians fail is that they fall victim to a third myth about power. They mistakenly believe that power is acquired strategically in deceptive gamesmanship and by pitting others against one another. Here Machiavelli failed to appreciate an important fact in the evolution of human hierarchies: that with increasing social intelligence, subordinates can form powerful alliances and constrain the actions of those in power. Power increasingly has come to rest on the actions and judgments of other group members. A person’s power is only as strong as the status given to that person by others.

The sociologist Erving Goffman wrote with brilliant insight about deference—the manner in which we afford power to others with honorifics, formal prose, indirectness, and modest nonverbal displays of embarrassment. We can give power to others simply by being respectfully polite.

My own research has found that people instinctively identify individuals who might undermine the interests of the group, and prevent those people from rising in power, through what we call “reputational discourse.” In our research on different groups, we have asked group members to talk openly about other members’ reputations and to engage in gossip. We’ve found that Machiavellians quickly acquire reputations as individuals who act in ways that are inimical to the interests of others, and these reputations act like a glass ceiling, preventing their rise in power. In fact, this aspect of their behavior affected their reputations even more than their sexual morality, recreational habits, or their willingness to abide by group social conventions.

In The Prince, Machiavelli observes,

“Any man who tries to be good all the time is bound to come to ruin among the great number who are not good. Hence a prince who wants to keep his authority must learn how not to be good, and use that knowledge, or refrain from using it, as necessity requires.”

He adds, “A prince ought, above all things, always to endeavor in every action to gain for himself the reputation of being a great and remarkable man.” By contrast, several Eastern traditions, such as Taoism and Confucianism, exalt the modest leader, one who engages with the followers and practices social intelligence. In the words of the Taoist philosopher Lao-tzu, “To lead the people, walk behind them.” Compare this advice to Machiavelli’s, and judge them both against years of scientific research. Science gives the nod to Lao-tzu.


Did Life On Earth Actually Originate On Mars?

With last week’s news that NASA’s Mars Curiosity rover detected "tough" organic molecules in 3-billion-year-old sedimentary rocks within five centimeters of the surface, at least one prominent planetary scientist thinks that the debate over whether Mars first seeded Earth with life or vice-versa will only intensify.

This low-angle self-portrait of NASA's Curiosity Mars rover shows the vehicle at the site from which . [+] it reached down to drill into a rock target called "Buckskin" on lower Mount Sharp.

The findings appeared in last week’s issue of the journal Science along with a second paper which noted that Curiosity has also detected seasonal variations in minuscule amounts of Mars’ atmospheric methane.

But the $64,000 question remains: if life arose on Mars did it do so independently? Or did one planet seed the other through the meteoritic exchange of organics or even biota? This is the ultimate conundrum, Cornell University planetary scientist Jonathan Lunine, told me.

For as some astrobiologists have long argued, if we find evidence that life arose independently on Mars --- only the next planet out, then it’s only logical to conclude that life in the cosmos is very common indeed.

“ Curiosity struck organic gold in Gale Crater because it was once a lake environment, where organics would have been concentrated and preserved in sediments,” Lunine told me.

NASA reports that some of the molecules identified include thiophenes, benzene, toluene, and small carbon chains, such as propane or butene.

The sulfur that is dominant in these organics stabilizes them, greatly enhancing the possibility that they would survive in the soil for billions of years,” Lunine told me.

And given the evidence for habitable environments that may have lasted for hundreds of millions of years, life may have begun on Mars, Lunine says. But the exchange of microbes with Earth through large impacts, early in Mars’ history, might have cross-contaminated the two planets, he says.

But did life on our two planets actually first originate on Mars?

“This is the dilemma,” said Lunine. “Mars and Earth are close enough to have exchanged lots of material over the age of the solar system.”

But as I noted here previously, some researchers think that both ultraviolet radiation from the young Sun and galactic cosmic rays would have likely destroyed microbial life in the unprotected vacuum of space. And even if microbial life survived the journey to Earth, it’s doubtful it would have survived the trip through Earth’s atmosphere and then adapted to its new home.

Even so, Lunine counters that it’s too soon to say whether or not biota were shared. And even if we find life, these arguments will persist unless we find a living cell. Although he notes that is very unlikely, he says it would be required for researchers to be able to study the biochemistry of putative Martian life.

This is why I am keenly interested in Saturn’s moon of Enceladus it’s far enough away that interplanetary transfer of any such ancient life into the inner solar system would have been much less likely, says Lunine.

Although NASA says that while Curiosity has not determined the source of the organic molecules, data collected by the rover reveals that Gale Crater once held all the ingredients needed for life.

What are we missing in our current search for ancient and/or extant life on Mars?

Measuring the isotopic ratio of carbon in the gaseous methane—a measurement that requires great sensitivity---would help to constrain whether that methane is produced by water reacting with carbon dioxide and rock or by biology, says Lunine.

NASA’s Mars 2020 rover which should land on Mars in 2021, says Lunine, has an instrument payload that can detect organic compounds and look for chemical and imaging indications of life on millimeter scales. And the European Space Agency’s (ESA) ExoMars program includes ongoing orbital measurements to help map Mars’ methane, he says. The ExoMars rover will also look for life in samples that will be recovered from six-foot drills.

“This will be an excellent follow-on to Curiosity,” said Lunine.

The interior of Gale Crater from Vera Rubin Ridge, as seen by Curiosity’s mastcam.

As for what Gale Crater’s ancient lakeshore might have looked like?

Some 3.1 to 3.billion years ago Lunine says the area would have been filled with liquid water, with streams feeding the lake caldera from the surrounding region. Mars would have had a bluer sky and a thicker atmosphere , but by how much is still under debate, he says. But even in Mars’ astrobiological heyday, he notes Gale Crater would hardly evoke images of a “Caribbean vacay.”

Even so, the discovery of near-surface complex organics that survived over billion-year timescales is “stunning,” Mark Lemmon, atmospheric scientist at Texas A&M University in College Station and a member of the Curiosity science team, told me.

“I imagine most organics wouldn't have [survived], so the implication is that there could have been much more,” Lemmon told me.


Quantum vacuum: Less than zero energy

Energy is a quantity that must always be positive -- at least that's what our intuition tells us. If every single particle is removed from a certain volume until there is nothing left that could possibly carry energy, then a limit has been reached. Or has it? Is it still possible to extract energy even from empty space?

Quantum physics has shown time and again that it contradicts our intuition -- and this is also true in this case. Under certain conditions negative energies are allowed, at least in a certain range of space and time. An international research team at the TU Vienna, the Université libre de Bruxelles (Belgium) and the IIT Kanpur (India) have now investigated the extent to which negative energy is possible. It turns out that no matter which quantum theories are considered, no matter what symmetries are assumed to hold in the universe, there are always certain limits to "borrowing" energy. Locally, the energy can be less than zero, but like money borrowed from a bank, this energy must be "paid back" in the end.

Repulsive Gravity

"In the theory of general relativity, we usually assume that the energy is greater than zero, at all times and everywhere in the universe," says Prof. Daniel Grumiller from the Institute for Theoretical Physics at the TU Wien (Vienna). This has a very important consequence for gravity: Energy is linked to mass via the formula E=mc². Negative energy would therefore also mean negative mass. Positive masses attract each other, but with a negative mass, gravity could suddenly become a repulsive force.

Quantum theory, however, allows negative energy. "According to quantum physics, it is possible to borrow energy from a vacuum at a certain location, like money from a bank," says Daniel Grumiller. "For a long time, we did not now about the maximum amount of this kind of energy credit and about possible interest rates that have to be paid. Various assumptions about this "interest" (known in the literature as "Quantum Interest") have been published, but no comprehensive result has been agreed upon.

The so-called "Quantum Null Energy Condition" (QNEC), which was proven in 2017, prescribes certain limits for the "borrowing" of energy by linking relativity theory and quantum physics: An energy smaller than zero is thus permitted, but only in a certain range and only for a certain time. How much energy can be borrowed from a vacuum before the energetic credit limit has been exhausted depends on a quantum physical quantity, the so-called entanglement entropy.

"In a certain sense, entanglement entropy is a measure of how strongly the behavior of a system is governed by quantum physics," says Daniel Grumiller. "If quantum entanglement plays a crucial role at some point in space, for example close to the edge of a black hole, then a negative energy flow can occur for a certain time, and negative energies become possible in that region."

Grumiller was now able to generalize these special calculations together with Max Riegler and Pulastya Parekh. Max Riegler completed his dissertation in the research group of Daniel Grumiller at the TU Wien and is now working as a postdoc in Harvard. Pulastya Parekh from the IIT in Kanpur (India) was a guest at the Erwin Schrödinger Institute and at the TU Wien.

"All previous considerations have always referred to quantum theories that follow the symmetries of Special Relativity. But we have now been able to show that this connection between negative energy and quantum entanglement is a much more general phenomenon," says Grumiller. The energy conditions that clearly prohibit the extraction of infinite amounts of energy from a vacuum are valid for very different quantum theories, regardless of symmetries.

The law of energy conservation cannot be outwitted

Of course, this has nothing to do with mystical "over unity machines" that allegedly generate energy out of nothing, as they are repeatedly presented in esoteric circles. "The fact that nature allows an energy smaller than zero for a certain period of time at a certain place does not mean that the law of conservation of energy is violated," stresses Daniel Grumiller. "In order to enable negative energy flows at a certain location, there must be compensating positive energy flows in the immediate vicinity."

Even if the matter is somewhat more complicated than previously thought, energy cannot be obtained from nothing, even though it can become negative. The new research results now place tight bounds on negative energy, thereby connecting it with quintessential properties of quantum mechanics.


5 Super Zika

By now, the entire world has learned to fear the Zika virus. The disturbing birth defects caused by the illness are scary enough, but the virus&rsquo ability to quickly mutate is another cause for concern. It changes faster than we can figure it out due to its ability to absorb foreign DNA.

According to University of Buckingham researchers, that&rsquos more dangerous than we realize. They believe that the only explanation for the virus&rsquo random adaptations&mdashsuch as the sudden ability to transmit via sexual contact&mdashis the absorption of alien DNA.

Claiming that alien microbes are constantly being delivered to Earth by space debris, the researchers think Zika is using the extraterrestrial genes to beef itself up. Unless action is taken, they say, the virus will mutate out of control and threaten humanity. So, uh, consider yourself warned.


Physicists Say They've Manipulated 'Pure Nothingness' And Observed The Fallout

According to quantum mechanics, a vacuum isn't empty at all. It's actually filled with quantum energy and particles that blink in and out of existence for a fleeting moment - strange signals that are known as quantum fluctuations.

For decades, there had only ever been indirect evidence of these fluctuations, but back in 2015, researchers claimed to have detected the theoretical fluctuations directly. And now the same team says they've gone a step further, having manipulated the vacuum itself, and detecting the changes in these strange signals in the void.

We're entering the territory of high-level physics here, but what's really important in this experiment is that, if these results are confirmed, the researchers might have just unlocked a way to observe, probe, and test the quantum realm without interfering with it.

That's important, because one of the biggest problems with quantum mechanics - and our understanding of it - is that every time we measure and observe a quantum system, we destroy it, which doesn't bode well when we want to tease out what's really going on in the quantum world.

This is where the quantum vacuum comes into it.

First of all, let's think of a vacuum in a classical way - as space entirely devoid of matter, with the lowest possible energy. There are no particles there, and nothing to interfere with pure physics.

But a byproduct of one of the most fundamental principles in quantum mechanics, Heisenberg's uncertainty principle, states that there's a limit to how much we can know about quantum particles, and as a result, a vacuum isn't empty, it's actually buzzing with its own strange energy, and filled with particle-antiparticle pairs that appear and disappear randomly.

These are more like 'virtual' particles than physical matter, so ordinarily you can't detect them. But although they're invisible, like most things in the quantum world, they subtly influence the real world.

These quantum fluctuations produce randomly fluctuating electric fields that can affect electrons, which is how scientists first indirectly demonstrated their presence back in the 1940s.

For decades, that was all we had to go on.

Then, in 2015, a team led by Alfred Leitenstorfer from the University of Konstanz in Germany claimed they'd directly detected these fluctuations, by observing their influence on a light wave. The results were published in Science.

To do this, they fired a super short laser pulse - lasting only a few femtoseconds, which is a millionth of a billionth of a second - into a vacuum, and were able to see subtle changes in the polarisation of the light. They said these changes were caused directly by the quantum fluctuations.

It's a claim that's still being debated, but the researchers have now taken their experiment to the next level by 'squeezing' the vacuum, and say they've been able to observe the strange changes in the quantum fluctuations as a result.

This isn't just further evidence of the existence of these quantum fluctuations - it also suggests that they've come up with a way to observe experiments in the quantum world without messing up the results, which is something that would ordinarily destroy the quantum state.

"We can analyse quantum states without changing them in the first approximation," said Leitenstorfer.

Usually when you're looking for the effects of quantum fluctuations on a single light particle, you'd have to detect that light particle, or amplify it, in order to see the effect. And this would remove the 'quantum signature' left on that photon, which is similar to what the team did in the 2015 experiment.

This time, instead of looking at the changes in quantum fluctuations by absorbing and amplifying photons of light, the team studied light on the time domain.

That sounds weird, but in a vacuum, space and time behave in the same way, so it's possible to examine one to learn more about the other.

Doing this, the team saw that when they 'squeezed' the vacuum, it worked kind of like squeezing a balloon, and redistributed the strange quantum fluctuations within it.

At some points, the fluctuations became way louder than the background 'noise' of an unsqueezed vacuum, and in some parts, they were quieter.

Leitenstorfer compares this to a traffic jam - when there's a bottleneck that cars build up behind, in front of that point, the density of cars will decrease again.

The same thing happens in a vacuum, to a certain extent - as the vacuum gets squeezed in one place, the distribution of the quantum fluctuations changes, and they can speed up or slow down as a result.

That effect can be measured on the time domain, which you can see below charted out on space-time. The bump in the middle is the 'squeeze' in the vacuum:

As you can see, as a result of the squeeze, there are some blips in the fluctuations.

But something else weird happens too, the fluctuations in some places appear to drop below the background noise level, which is lower than the ground state of empty space, something the scientists call an "astonishing phenomenon".

"As the new measurement technique neither has to absorb the photons to be measured nor amplify them, it is possible to directly detect the electromagnetic background noise of the vacuum and thus also the controlled deviations from this ground state, created by the researchers," explains a press release.

The team is now testing just how accurate their technique is, and how much they can learn from it.

Even though the results so far are impressive, there's still a chance the team might have only achieved a so-called weak measurement - a type of measurement that doesn't disturb the quantum state, but doesn't actually tell researchers very much about a quantum system.

If they can learn more using this technique, they want to continue to use it to probe the 'quantum state of light', which is the invisible behaviour of light at the quantum level that we're only just beginning to understand.

Further verification is needed to replicate the team's findings and show that their experiment really works. But it's a pretty cool first step.


Scientists create 'alien' life form with artificial genetic code

For the first time, researchers create a new organism based on E. coli that passes along artificially engineered DNA.

/>From left to right, the structures of A-, B- and Z-DNA. Zephyris/Wikipedia

Scientists made a substantial breakthrough in understanding how to alter the fundamental nature of life, and they did so by creating for the first time a partially artificial life form that passes along lab-engineered DNA.

The work, published online in the journal Nature on Wednesday, came from the Scripps Research Institute in La Jolla, Calif., and centered around a modified strain of E. coli bacterium that was fused with chemically synthesized nucleotides and was able to replicate its natural and synthetic components during reproduction.

Throughout the entire history of life on Earth, the genetic code of all organisms has been uniform, from the simplest of bacteria all the way up to human beings, meaning our genetic code is composed of the same four nucleotides labeled A, C, T, and G. Those nucleotides join to form base pairs, which are used in the creation of genes that cells use to produce proteins.

Researchers at Scripps created two new nucleotides, X and Y, and fused them into the E. coli bacterium. The organism was able to reproduce normally with six -- instead of the standard four -- nucleotides, meaning it genetically passed along the first combination of manmade and natural DNA.

"This has very important implications for our understanding of life," Floyd Romesberg, who headed the Scripps researcher team, told The New York Times. "For so long people have thought that DNA was the way it was because it had to be, that it was somehow the perfect molecule."

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Not only can these artificially created organisms be used to generate new medicines as base pairs are the source of proteins, but it also has applications in understanding life itself, from the sustainability of alien forms that differ from our own genetic makeup to the secrets of Earth's living organism construction.

Because this breakthrough could impact more than just biological research, the field -- called synthetic biology -- is likely to be met with harsh criticism from those who fear that tampering with the building blocks of existence could be a step too far for science. The subset of synthetic biology focusing on creations unfamiliar to nature with expanded genetic alphabets is sometimes referred to as xenobiology.

"The arrival of this unprecedented 'alien' life form could in time have far-reaching ethical, legal and regulatory implications," Jim Thomas of the ETC Group, a Canadian advocacy organization, told The New York Times. "While synthetic biologists invent new ways to monkey with the fundamentals of life, governments haven't even been able to cobble together the basics of oversight, assessment or regulation for this surging field."

To create a modified organism that would reproduce, Romesberg's team had to first create stable enough artificial nucleotides. The creation of X and Y variants came only after 300 types were tried. The X nucleotide pairs with the Y, just as A does with T and C with G in natural DNA. It's unclear whether a semi-artificial organism could sustain a far more expansive genetic code, meaning many more synethic pairs, and if there is any time-based restraint involved.

As far as worrying about never-before-seen strains of bacteria escaping into the wild, Romesberg stressed that this newly created organism could never infect anything. To continue reproducing the synthetic nucleotides, the researchers had to feed the necessary chemicals to the bacterium or else it would stop producing the X and Y pair.

Romesberg and his colleagues' findings follow decades of work in synthetic biology, and the results have long since left the confines of academic research. Romesberg's company, Synthorx, is trying to design an administering technique for viruses that would rely on the artificial life forms' inability to reproduce the synthetic nucleotides without the proper chemicals, meaning they could be used to create an immune system response while be inhibited from spreading.

Beyond those immediate applications, the next steps are figuring out if the synthesized nucleotides can be fused into the RNA of living organisms and used to produce new proteins, as well as discovering whether or not genetically engineered cells could be used to help organisms reproduce those synthetic nucleotides on their own.



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