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Can a second mass extinction by microbes happen?

Can a second mass extinction by microbes happen?



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Science Daily reports that the mass extinction at the end of Permian period happened by the Methanosarcina archaea wiping out 90% of species:

Methane-producing microbes may be responsible for the largest mass extinction in Earth's history. Fossil remains show that sometime around 252 million years ago, about 90 percent of all species on Earth were suddenly wiped out [… ]. It turns out that Methanosarcina had acquired a particularly fast means of making methane, and the team's detailed mapping of the organism's history now shows that this transfer happened at about the time of the end-Permian extinction.

Is it possible by the global warming and all the spores of bacteria come out from melting glacier or anywhere else and mass extinction occur?


First of all, let's consider your Methanosarcina scenario in specific.

Methanosarcina with those properties are still around. So, there is no reason to expect that introducing some ancient Methanosarcina into a suitable environment today would do very much - as they should already be there. Any existing (large-scale) environment providing a niche for Methanosarcina should already be occupied by it as it only needs a single organism to get there by chance at some point.

Moreover, there must be some reason why our atmosphere stopped being filled with methane by Methanosarcina. For example some prerequisite resource could have been depleted, some other organism evolved that consumes this methane or controls the Methanosarcina population by feeding on it. Whatever this reason is, we should expect that it still applies: A required resource would still be gone and a second organism controlling this activity should still be around (or resurface together with the Methanosarcina in question). In fact, the hypothesis you mention maintains that the nickel required by Methanosarcina to produce methane was available in huge amounts due to specific volcanic activity at that time.

Finally, the current ice masses of the Earth are much younger and have not been around since the Permian period. In general, if geologically cryostoring microbes were relevant, climate change should be the least of our worries as drilling a hole into the ice or local geologic activity could suffice to bring back a few individuals - which is all that would be needed.

Now, what about unfreezing microbes in general? Due to lack of fossils, we have little knowledge about microbe extinction, except that it does happen. However, my ecological intuition is that microbes either lose their niche to a fitter alternative (which either be more apt at causing problems or avoid them resurfacing) or survive in small amounts (ready to occupy their niche if it should resurface). Microbes are considerably different from higher, sexually reproducing life forms here as it only needs a single individual to revive the species and individuals can survive for a long time in adverse conditions, not only by sporulation but also because they need little energy to maintain their state. Finally, if a niche for disastrous microbes exists, there is the constant risk that it will be filled by some ordinary microbes evolving, which brings us to the next point.

Something that is conceivable to happen is that some microbes spontaneously evolve to fill a big niche and have some disastrous by product leading to a mass extinction. It is hard to estimate this risk, but as far as I know, there is no historic precedent after the evolution of higher life forms. (As elaborated above, the Methanosarcina hypothesis for the Permian extinction features additional factors.) However, I consider it unlikely that climate change increases this risk. While climate change undoubtedly has disastrous ecological consequences, tilting individual ecosystems, I don't see how it creates some fundamentally new environment (that wasn't already there in similar form somewhere else on the planet) that would stimulate a spontaneous disastrous microbial evolution.


Can a second mass extinction by microbes happen? - Biology

The number of species on the planet, or in any geographical area, is the result of an equilibrium of two evolutionary processes that are continuously ongoing: speciation and extinction. Both are natural “birth” and “death” processes of macroevolution. When speciation rates begin to outstrip extinction rates, the number of species will increase likewise, the number of species will decrease when extinction rates begin to overtake speciation rates. Throughout Earth’s history, these two processes have fluctuated—sometimes leading to dramatic changes in the number of species on Earth as reflected in the fossil record (Figure 1).

Figure 1. Percent extinction occurrences as reflected in the fossil record have fluctuated throughout Earth’s history. Sudden and dramatic losses of biodiversity, called mass extinctions, have occurred five times.

Paleontologists have identified five strata in the fossil record that appear to show sudden and dramatic (greater than half of all extant species disappearing from the fossil record) losses in biodiversity. These are called mass extinctions. There are many lesser, yet still dramatic, extinction events, but the five mass extinctions have attracted the most research. An argument can be made that the five mass extinctions are only the five most extreme events in a continuous series of large extinction events throughout the Phanerozoic (since 542 million years ago). In most cases, the hypothesized causes are still controversial however, the most recent event seems clear.


Research reveals resilience of sea life in the aftermath of mass extinctions

At the Cretaceous-Paleogene boundary, not only dinosaurs went extinct. The loss of species in the upper part of the ocean had profound impacts on its diversity and function. Image shows small deprived Cretaceous fauna after the extinction. Credit: Brian Huber

Pioneering research has shown marine ecosystems can start working again, providing important functions for humans, after being wiped out much sooner than their return to peak biodiversity.

The study, led by the University of Bristol and published today in Proceedings of the Royal Society B, paves study the way for greater understanding of the impact of climate change on all life forms.

The international research team found plankton were able to recover and resume their core function of regulating carbon dioxide levels in the atmosphere more than twice as fast as they regained full levels of biodiversity.

Senior author Daniela Schmidt, Professor of Palaeobiology at the University of Bristol, said: "These findings are hugely significant, given growing concern around the extinctions of species in response to dramatic environmental shifts. Our study indicates marine systems can accommodate some losses in terms of biodiversity without losing full functionality, which provides hope. However, we still don't know the precise tipping point so the focus should very much remain on preserving this fragile relationship and protecting biodiversity."

While previous research has shown that functionality resumes quicker than biodiversity in algae, this is the first study to corroborate the discovery further up the food chain in zooplankton, which are vital for sea life as part of the food web supporting fish.

The scientists analyzed tiny organisms called foraminifer, the size of grains of sand, from the mass extinction, known as the Cretaceous-Paleogene (K-Pg), which took place around 66 million years ago and eradicated three-quarters of the Earth's plant and animal species. This is the most catastrophic event in the evolutionary history of modern plankton, as it resulted in the collapse of one of the ocean's primary functions, the 'biological pump' which sucks vast amounts of carbon dioxide out of atmosphere into the ocean where it stays buried in sediments for thousands of years. The cycle not only influences nutrient availability for marine life, but also carbon dioxide levels outside the sea and therefore the climate at large.

Lead author Dr. Heather Birch, a former researcher at the university's School of Earth Sciences and Cabot Institute for the Environment, said: "Our research shows how long—approximately 4 million years—it can take for an ecosystem to fully recover after an extinction event. Given human impact on current ecosystems, this should make us mindful. However, importantly the relationship between marine organisms and the marine carbon pump, which affects atmosphere CO2, appears not to be closely related."

Professor Schmidt added: "The results highlight the importance of linking climate projections with ecosystems models of coastal and open ocean environments to improve our ability to understand and forecast the impact of climate-induced extinctions on marine life and their services to people, such as fishing. Further research is needed to look at what happens and whether the same patterns are evident higher up the food web, for instance with fish."


Coming: The sixth mass extinction?

Humans, without really intending to, brought down within decades the global number of passenger pigeons &mdash from at least 3 billion birds to just one. And that last passenger pigeon died Sept. 1, 1914. Human changes to Earth&rsquos ecosystem and climate now imperil many other species, putting them, too, at risk of extinction.

Louis Agassiz Fuertes/Wikimedia Commons

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October 17, 2014 at 10:05 am

Five times in Earth’s history, some three-quarters of all living species disappeared forever — and within a short period of time. These mass-extinction events marked the boundaries between different periods in geologic time. Those species losses reflect a major shift in the planet’s ecology. Clues to these shifts can be seen in the fossils and rock layers that form part of the geologic record.

Today, human activities are driving species to go extinct at a rate never before seen.

And this loss of species really does matter, says Anita Narwani. She’s an ecologist at the University of Michigan in Ann Arbor. That’s because the diversity of species in an ecosystem — the breadth of different organisms present — provide people with all types of services we can’t do without.

Trees provide oxygen for us to breathe. At the same time, they remove carbon from the air. That carbon is a contributor to global warming. Plants clean pollutants from air and water. Microbes break down waste. Animals disperse seeds that keep forests thriving. A broad range of living resources also provides people with food, shelter and medicine.

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Narwani wanted to find out just how important biodiversity is for people. So she teamed up with other ecologists to review more than 1,700 studies. They found that more diverse parts of the globe tend to excel at things like removing carbon and providing us with wood and other natural resources. They also were better at keeping fisheries large and healthy so that they could feed many people.

This saber-toothed cat is among the ice age animals that went extinct about 12,000 years ago. They were part of a mass die-off called the Quaternary extinction. Cicero Moraes/Wikimedia Commons (CC BY-SA 3.0)

The findings suggest people benefit greatly from there being a diverse range of species.

Unfortunately, biodiversity is in steep decline.

It is too soon to declare that Earth is undergoing a sixth mass extinction, Narwani says. She defines a mass extinction as the loss of 75 percent of species over 2 million years or less. We haven’t lost that many — at least not yet. But if current rates of species losses continue, such a mass extinction could occur in just 300 years.

“This is a very short time relative to the time frame for the previous mass events,” she points out. Such an event would leave a telltale absence of many species in the fossil record. From that point on, fossils of the vanished species would no longer appear in the pages of Earth’s rock-based diary.

The new findings highlight the potential for humans to erase many of the resources on which we now depend. As people learn more, however, they can take steps to lessen those risks. For example, by using natural resources more efficiently, says Narwani, people can preserve ecosystems so that they can continue to provide us with their services.

Power Words

biodiversity The number and variety of organisms found within a geographic region.

carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

diversity (in biology) A range of different life forms.

ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

extinction The state or process of a species, family or larger group of organisms ceasing to exist.

fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils.

geologic time The span of time that covers Earth’s 4.5 billion-year history. Scientists divide geologic time into successively briefer intervals of time, called eons, periods, epochs, eras and ages.

geologic record Mineral deposits and fossils that form in rock. Geologists can “read” these minerals to decipher what Earth’s climate and geology was like (such as dry spells, earthquakes or volcanic eruptions) when the rock’s ingredients were laid down. Fossils and other mineral can signal what life may have existed at the same time.

geology The study of Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists. Planetary geology is the science of studying the same things about other planets.

global warming The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.

mass extinction Loss of 75 percent of the world’s species in a short time period, typically defined as 2 million years or less. Our planet has experienced 5 known mass extinctions.

microorganism,or microbe A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

Quaternary Period A time in the distant past that was defined by regular ice ages. It began about 2.58 million years ago. Scientists refer to its earliest period as the Pleistocene. Then, about 11,700 years ago, a second period began, known as the Holocene. It continues through today.

species A group of similar organisms capable of producing offspring that can survive and reproduce.

Citations

S. Ornes. “Mammals feel the heat.” Science News for Students. June 5, 2012.

S. Ornes. “Sea changes.” Science News for Students. April 7, 2011.

S. Ornes. “The carbon dioxide coral generation.” Science News for Students. November 22, 2010.

Original journal source: B. Cardinale, et al. . Nature. June 7, 2012. doi: 10.1038/nature11148.

About Alison Pearce Stevens

Alison Pearce Stevens is a former biologist and forever science geek who writes about science and nature for kids. She lives with her husband, their two kids and a small menagerie of cuddly (and not-so cuddly) critters.

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Biology Lesson 2/6/09 – Graph of Mass Extinctions and website

2. DO NOT ENTER ANY LETTERS OR WORDS. Enter the numbers for millions of years in Column A number of families in Column B.

Millions of years: 525, 510, 500, 475, 450, 440, 435, 415, 410, 400, 380, 370, 350, 333, 325, 240, 235, 220, 205, 100, 80, 65, 0

# of Families: 100, 180, 160, 300, 410, 405, 325, 425, 430, 425, 440, 440, 367, 395, 435, 375, 210, 380, 240, 550, 600, 630, 760

3. Pull down Insert menu. Select Chart. Select (XY) Scatter. Select the graph with connected points. Click Next. Click Next (again).

4. Chart Title: Mass Extinctions – Your Name. Value (X) Axis: millions of years ago. Value (Y) Axis: number of families. Click Next.

5. Select As New Sheet. Print out and tape/glue/staple in your notebook.

1. For each mass extinction #1-5, write how many million years ago each extinction happened (you get this by looking at the graph).

2. The series of mass extinctions 488 million years ago eliminated many ________________ and __________________ and severely reduced the number of ________________ species.


Mass extinctions and ocean acidification: biological constraints on geological dilemmas

The five mass extinction events that the earth has so far experienced have impacted coral reefs as much or more than any other major ecosystem. Each has left the Earth without living reefs for at least four million years, intervals so great that they are commonly referred to as ‘reef gaps’ (geological intervals where there are no remnants of what might have been living reefs). The causes attributed to each mass extinction are reviewed and summarised. When these causes and the reef gaps that follow them are examined in the light of the biology of extant corals and their Pleistocene history, most can be discarded. Causes are divided into (1) those which are independent of the carbon cycle: direct physical destruction from bolides, ‘nuclear winters’ induced by dust clouds, sea-level changes, loss of area during sea-level regressions, loss of biodiversity, low and high temperatures, salinity, diseases and toxins and extraterrestrial events and (2) those linked to the carbon cycle: acid rain, hydrogen sulphide, oxygen and anoxia, methane, carbon dioxide, changes in ocean chemistry and pH. By process of elimination, primary causes of mass extinctions are linked in various ways to the carbon cycle in general and ocean chemistry in particular with clear association with atmospheric carbon dioxide levels. The prospect of ocean acidification is potentially the most serious of all predicted outcomes of anthropogenic carbon dioxide increase. This study concludes that acidification has the potential to trigger a sixth mass extinction event and to do so independently of anthropogenic extinctions that are currently taking place.

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Evidence for a changing climate today in the Anthropocene

The following information is from OpenStax Biology 2e 44.5.

Climate change can be understood by approaching three areas of study:

  • drivers of global climate change
  • evidence of current and past global climate change
  • documented results of climate change

It is helpful to keep these three different aspects of climate change clearly separated when consuming media reports about global climate change. We should note that it is common for reports and discussions about global climate change to confuse the data showing that Earth’s climate is changing with the factors that drive this climate change.

Climate refers to the long-term, predictable atmospheric conditions of a specific area, while weather refers to the conditions of the atmosphere during a short period of time. To better understand the difference between climate and weather, imagine that you are planning an outdoor event in Atlanta. You would be thinking about climate when you plan the event in the fall or spring rather than the summer because you have long-term knowledge that any given Saturday in the months of May to August will likely be hot! However, you cannot guarantee temperate and cool weather on any specific Saturday because it is difficult to accurately predict the weather. A common misconception about global climate change is that a specific weather event occurring in a particular region, like rainstorm in Georgia, provides evidence of global climate change. Instead, a rainstorm is a weather-related event and not a climate-related one. Climate can be considered “average” weather that takes place over many years.

The Earth has gone through periodic cycles of increases and decreases in temperature. The natural drivers of climate change include Milankovitch cycles, changes in solar activity, and volcanic eruptions.

The Milankovitch cycles describe the effects of slight changes in the Earth’s orbit on Earth’s climate. These range in length between 19,000 and 100,000 years, which are huge time scales relative to human activity.

Solar intensity is the amount of solar power or energy the sun emits in a given amount of time. As solar intensity increases (or decreases), the Earth’s temperature correspondingly increases (or decreases). Changes in solar intensity have been proposed as one of several possible explanations for the Little Ice Age.

Volcanic eruptions last a few days, but the solids and gases released can influence the climate over a period of a few years, causing short-term climate changes, generally cooling the climate. The output of gases and solids released by volcanic eruptions into the atmosphere can include carbon dioxide, water vapor, sulfur dioxide, hydrogen sulfide, hydrogen, and carbon monoxide. They establish a haze that block out sunlight and triggers climate cooling globally, often lasting one or more years.

None of these factors, however, leads to rapid increases in global temperature or sustained increases in carbon dioxide. For an explanation of the current upward spike in temperatures, we have to look to anthropogenic drivers of climate change. Greenhouse gases are probably the most significant drivers of the climate. When heat energy from the sun strikes the Earth, atmospheric gases like carbon dioxide, methane, water vapor, nitrous oxide, and ozone trap the heat in the atmosphere, similar to how the glass panes of a greenhouse keep heat from escaping. These gasses are necessary for life on the surface because they help protect terrestrial species from the DNA-damaging UV from the sun. In fact, only about half of the radiation from the sun passes through these gases in the atmosphere to reach the surface. Once, here, sunlight radiation is converted into thermal (infrared) radiation, and then a portion of that energy is re-radiated back into the atmosphere. However, those same gasses reflect much of the thermal energy back to the Earth’s surface. The more greenhouse gasses there are in the atmosphere, the more thermal energy is reflected back to the Earth’s surface, heating it up and the atmosphere immediately above it. Greenhouse gases absorb and emit radiation and are an important factor in the greenhouse effect: the warming of Earth due to carbon dioxide and other greenhouse gases in the atmosphere.

The burning of fossil fuels is an important source of greenhouse gases, which play a major role in the greenhouse effect.


Mass Extinctions of Earth

History of Life on Earth Geological Time Spiral USGS (Public Domain/Wikimedia Commons)
Cr: https://medium.com/360-on-history/earths-ancient-mass-extinctions-28792d9fd81d

Mass extinction can be defined as the rapid reduction in the biodiversity of the planet. The extinction of huge verities of species rapidly is because of catastrophic natural event or changes in the environment that is not possible for adaption by several species. Life on earth has recovered at most five mass extinctions in the last 500 million years that resulted in the extinction of about 99 percent of species from the Earth that ever existed. The occurrence of mass extinction gives rise to the foundation of a new era. When new species evolve to survive under changed circumstances, the old species that are unable to adopt these changes start to extinct (Michael Greshko, 2019).

Mass extinction can also be termed as an abiotic crisis or extinction event and is defined as a rapid reduction in the biodiversity of the environment. It is considered to occur when the extinction rate is much higher than the speciation rate. The fossils of marine species are mostly used to calculate the rate of extinction. It is said that the first major mass extinction event occurred about 2.5 billion years ago and is known as the great oxidation event. After the Cambrian explosion, five further mass extinction occurred on the earth (D.M. Raup and J.J. Sepkoski Jr., 1982).

List of Mass Extinctions

The mass extinctions can be identified in the records of fossils that can be collected from the surface of the earth. There are a total of five mass extinctions in the history of the earth that are enlisted and described below –

1. Ordovician Silurian Extinction – The first mass extinction occurred about 440 million years ago that resulted in the extinction of small marine organisms.

2. Devonian Extinction –The second mass extinction occurred about 365 million years ago that resulted in the extinction of several tropical marine species.

3. Permian-Triassic Extinction – The third mass extinction took place about 250 million years ago and is considered the biggest mass extinction is known in history. It resulted in the extinction of about 90 percent of the vertebrates and marine species.

4. Triassic-Jurassic Extinction – The fourth mass extinction occurred about 210 million years ago that resulted in the extinction of several other vertebrates and land species from earth.

5. Cretaceous-Tertiary Extinction – The fifth mass extinction occurred about 65.5 million years ago that resulted in the extinction of about 75 percent of the species. It is considered that the main cause behind this catastrophic extinction was the meteorite collision.

Causes of Mass Extinction

The most important reason for the mass extinction of earth is the deforestation as well as poaching. Both reasons involve the human act and greed and we can say that the true cause for the extinction of any species is the human. Humans poached various species for their satisfaction and unnecessary fulfillment. Other reasons for mass extinctions include the environmental changes, many species are unable to adapt to the changes that occurred in their surroundings and start to extinct, loss or sudden reduction in their sources of foods, catastrophic climatic or natural disasters. The extinction can also be done by some other world events like the crashing of asteroids or meteorites on the earth’s surface. About 65 million years ago, various species including dinosaurs got extinct when a meteorite of width about 6 miles crashed the earth’s surface (P.R. Ehrlich and A.H. Ehrlich, 1981).

Hence we can say that the major causes of mass extinction can be referred to as the rapid changes in the earth’s atmosphere, ecology, and surface. Several natural occurrences like floods, volcanic eruptions, falling of sea level and collision of asteroids and meteorites are considered the second reason for mass extinction. Global warming, methane eruptions, deforestation, anoxic events, global cooling, poaching of species are also considered as the reasons behind the species extinction.

Graphic on Earth’s “mass extinctions” during the last 500 years
Cr: https://phys.org/news/2019-04-earth-major-mass-extinctions.html

Sixth Mass Extinction

The sixth mass extinction is also known as the Anthropocene extinction or the Holocene extinction and is considered the most serious extinction of civilization because the extinction this time will be permanent. The sixth extinction of species on earth will be much faster as compared to the previous five extinctions that occurred on the earth. For example, the extinction of Mauritius’s Dodo and Russian Steller’s sea cow (G. Ceballos, 2015). In this ongoing extinction, there would be the disappearance of several species like megafauna. According to the researcher’s theory, the over poaching done by humans added much stress to the occurrence of this catastrophic mass extinction in the biodiversity. It is considered that half of the life forms of the Earth would extinct by the year 2100 because of tremendous disruptions caused by humans (Edward Osborne Wilson, 2002).

The main reason to cause sixth extinction is deforestation, global warming, ecological imbalance, and environmental disruptions. All these factors are mainly caused due to unnecessary human activities (J.A. Estes, A. Burdin, and D.F. Doak, 2016).

Prevention Techniques

There are several techniques that could be adapted to avoid the sixth extinction occurrence. We must try to avoid over-exploitation of several natural resources as this is the major reason behind the extinction of several species in the last 50 decades. We also must prevent the natural habitat of rare and important species and also focus on their conservation as well as conservation of their habitat. The importance of practicing afforestation should be taught to each and every human being and also suggest them to reduce the emission of greenhouse gases in the environment. Several camps must be organized in order to create awareness about the significance of the diversity of species to the ecosystem and understand the techniques for preventing our biodiversity (S.L. Pimm et al, 2014).

The mass extinction event has caused a disastrous situation in which several species extinct. In present only 1 to 2 percent living organism is alive and the rest got extinct with time. Natural disasters cannot be controlled however but human actions are also boosting the speed of occurrence of mass extinction on a large scale. This is needed to create awareness among people that their inhuman activities are responsible for these catastrophic events. Poaching of species, deforestation, and emission of greenhouse gases must be controlled.

D. M. Raup, J. J. Sepkoski Jr., Mass extinctions in the marine fossil record. Science 215, 1501–1503 (1982).

Edward Osborne Wilson, “In The Future of Life” , Harvard (2002).

G. Ceballos et al., Accelerated modern human-induced species losses: Entering the sixth mass extinction. Sci. Adv. 1, e1400253 (2015).

G. Ceballos, P. R. Ehrlich, A. H. Ehrlich, The Annihilation of Nature: Human Extinction of Mammals and Birds, (Johns Hopkins Press, Baltimore, MD, 2015).

G. Ceballos, P. R. Ehrlich, Mammal population losses and the extinction crisis. Science 296, 904–907 (2002).

J. A. Estes, A. Burdin, D. F. Doak, Sea otters, kelp forests, and the extinction of Steller’s sea cow. Proc. Natl. Acad. Sci. U.S.A. 113, 880–885 (2016).

Michael Greshko (26 September 2019), “What are mass extinctions, and what causes them?”, accessed on 22nd May 2021, <https://www.nationalgeographic.com/science/article/mass-extinction?cmpid=int_org=ngp::int_mc=website::int_src=ngp::int_cmp=amp::int_add=amp_readtherest>

P. R. Ehrlich, A. H. Ehrlich, Extinction: The Causes and Consequences of the Disappearance of Species, (Random House, 1981).

S. L. Pimm et al., The biodiversity of species and their rates of extinction, distribution, and protection. Science 344, 1246752 (2014).


Can a second mass extinction by microbes happen? - Biology

The vast majority of species that have ever lived went extinct sometime other than during one of the great mass extinction events. In spite of this, mass extinctions are thought to have outsized effects on the evolutionary history of life. While part of this effect is certainly due to the extinction itself, I here consider how the aftermaths of mass extinctions might contribute to the evolutionary importance of such events. Following the mass loss of taxa from the fossil record are prolonged intervals of ecological upheaval that create a selective regime unique to those times. The pacing and duration of ecosystem change during extinction aftermaths suggests strong ties between the biosphere and geosphere, and a previously undescribed macroevolutionary driver — earth system succession. Earth system succession occurs when global environmental or biotic change, as occurs across extinction boundaries, pushes the biosphere and geosphere out of equilibrium. As species and ecosystems re-evolve in the aftermath, they change global biogeochemical cycles — and in turn, species and ecosystems — over timescales typical of the geosphere, often many thousands to millions of years. Earth system succession provides a general explanation for the pattern and timing of ecological and evolutionary change in the fossil record. Importantly, it also suggests that a speed limit might exist for the pace of global biotic change after massive disturbance — a limit set by geosphere–biosphere interactions. For mass extinctions, earth system succession may drive the ever-changing ecological stage on which species evolve, restructuring ecosystems and setting long-term evolutionary trajectories as they do.


Can a second mass extinction by microbes happen? - Biology

What causes mass extinctions?

Although the best-known cause of a mass extinction is the asteroid impact that killed off the non-avian dinosaurs, in fact, volcanic activity seems to have wreaked much more havoc on Earth's biota. Volcanic activity is implicated in at least four mass extinctions, while an asteroid is a suspect in just one. And even in that case, it's difficult to disentangle how much of the end-Cretaceous extinction was caused by the asteroid and how much was caused by the steady ooze of lava that was blanketing most of India at around the same time.

While multiple causes may have contributed to many mass extinctions, all the hypothesized causes have two things in common: they cause major changes in Earth systems — its ecology, atmosphere, surface, and waters — at rapid rates. Here are some hypothesized causes for each of Earth's biggest mass extinctions:

End-Devonian extinction: • Climate change, possibly linked to the diversification of land plants • Decrease in oxygen levels in the deep ocean

End-Permian extinction: • Volcanic activity • Climate change • Decrease in oxygen levels in the deep ocean • Changes in atmospheric chemistry • Changes oceanic chemistry and circulation

End-Triassic extinction: • Volcanic activity

End-Cretaceous extinction: • Asteroid impact • Volcanic activity • Climate change • Changes in atmospheric and oceanic chemistry

What doesn't cause mass extinctions?
It may not come as much surprise that powerful volcanic eruptions and massive asteroid impacts can trigger mass extinctions. After all, we'd expect such disasters to bring about death and destruction. However, as paleontologists and geologists have studied Earth's history, they've noticed something interesting: sometimes, major catastrophes pass with hardly a blip in extinction rates. For example, the Manicouagan crater in Canada is several miles wide and constitutes strong evidence that a huge asteroid struck Earth one and a half million years ago — yet, the fossil record indicates no major dip in diversity associated with this event. Similarly, 2.5 km 3 of lava (called the Karoo-Ferrar volcanic province) covering what is now South Africa and Antarctica indicate extensive volcanic activity around 180 million years ago — yet despite this large-scale disruption, only a small rise in extinction rates occurred during that time period.


At left, the Manicouagan crater in Quebec as seen from space. At right, a researcher near exposures of the Ferrar flood basalts (dark rocks in the background) in Antarctica.

Why do some catastrophic events trigger mass extinctions and others do not? The devil seems to be in the details — particularly in the chain reaction of Earth systems disruptions that are triggered (or not) and in the rate at which those disruptions occur. Mass extinctions seem to occur when multiple Earth systems are thrown off kilter and when these changes happen rapidly — more quickly than organisms evolve and ecological connections adjust. For example, the asteroid that triggered the end-Cretaceous extinction happened to hit carbon-rich rocks, which probably led to ocean acidification, and hence the disruption of reef formation and the oceanic food web. However, the asteroid that caused the Manicouagan did not hit carbon-rich rocks and so did not set off this chain reaction or such a significant disruption of Earth systems. The Karoo-Ferrar volcanic activity, on the other hand, was so large that it would certainly have disrupted Earth's atmosphere and oceans however, in this case, the changes came about very slowly. The volcanic activity was spread over millions of years. For comparison, the volcanic activity that may have caused the end-Triassic mass extinction likely occurred in less than 100,000 years, leaving no time for evolution to take place as habitats changed and leading to widespread extinction.

Chart information from Barnosky, A.D., N. Matzke, S. Tomiya, G.O.U. Wogan, B. Swartz, T.B. Quental, … and E.A. Ferrer. 2011. Has the Earth's sixth mass extinction already arrived? Nature 471:51-57.

Photo of Manicouagan crater courtesy of NASA/JPL Ferrar flood basalts photo courtesy of Murray McClintock, Department of Geology, University of Otago, New Zealand [permission pending]


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