text: WASHINGTON (Reuters) - Sometimes bad things come in small packages. 
   
   A fossil of a trilobite, a horsecrab-like creature that thrived in the seas for hundreds of millions of years before becoming one of many kinds of animals wiped out in a mass extinction that befell the planet 252 million years ago, is shown in this handout photo provided by the University of Chicago March 31, 2014. REUTERS/Dan Dry/University of Chicago/Handout via Reuters 
   
   A microbe that spewed humongous amounts of methane into Earth’s atmosphere triggered a global catastrophe 252 million years ago that wiped out upwards of 90 percent of marine species and 70 percent of land vertebrates. 
   
   That’s the hypothesis offered on Monday by researchers aiming to solve one of science’s enduring mysteries: what happened at the end of the Permian period to cause the worst of the five mass extinctions in Earth’s history. 
   
   The scale of this calamity made the one that doomed the dinosaurs 65 million years ago - a six-mile wide asteroid smacking the planet - seem like a picnic by comparison. 
   
   The implicated microbe, Methanosarcina, is a member of a kingdom of single-celled organisms distinct from bacteria called archaea that lack a nucleus and other usual cell structures. 
   
   “I would say that the end-Permian extinction is the closest animal life has ever come to being totally wiped out, and it may have come pretty close,” said Massachusetts Institute of Technology biologist Greg Fournier, one of the researchers. 
   
   “Many, if not most, of the surviving groups of organisms barely hung on, with only a few species making it through, many probably by chance,” Fournier added. 
   
   Previous ideas proposed for the Permian extinction include an asteroid and large-scale volcanism. But these researchers suggest a microscope would be needed to find the actual culprit. 
   
   Methanosarcina grew in a frenzy in the seas, disgorging huge quantities of methane into Earth’s atmosphere, they said. 
   
   This dramatically heated up the climate and fundamentally altered the chemistry of the oceans by driving up acid levels, causing unlivable conditions for many species, they added. 
   
   The horseshoe crab-like trilobites and the sea scorpions - denizens of the seas for hundreds of millions of years - simply vanished. Other marine groups barely avoided oblivion including common creatures called ammonites with tentacles and a shell. 
   
   On land, most of the dominant mammal-like reptiles died, with the exception of a handful of lineages including the ones that were the ancestors of modern mammals including people. 
   
   ‘RADICALLY CHANGED’ 
   
   “Land vertebrates took as long as 30 million years to reach the same levels of biodiversity as before the extinction, and afterwards life in the oceans and on land was radically changed, dominated by very different groups of animals,” Fournier said. 
   
   The first dinosaurs appeared 20 million years after the Permian mass extinction. 
   
   “One important point is that the natural environment is sensitive to the evolution of microbial life,” said Daniel Rothman, an MIT geophysics professor who led the study published in the journal Proceedings of the National Academy of Sciences. 
   
   The best example of that, Rothman said, was the advent about 2.5 billion years ago of bacteria engaging in photosynthesis, which paved the way for the later appearance of animals by belching fantastic amounts of oxygen into Earth’s atmosphere. 
   
   Methanosarcina is still found today in places like oil wells, trash dumps and the guts of animals like cows. 
   
   It already existed before the Permian crisis. But genetic evidence indicates it acquired a unique new quality at that time through a process known as “gene transfer” from another microbe, the researchers said. 
   
   It suddenly became a major producer of methane through the consumption of accumulated organic carbon in ocean sediments. 
   
   The microbe would have been unable to proliferate so wildly without proper mineral nutrients. The researchers found that cataclysmic volcanic eruptions that occurred at that time in Siberia drove up ocean concentrations of nickel, a metallic element that just happens to facilitate this microbe’s growth. 
   
   Fournier called volcanism a catalyst instead of a cause of mass extinction - “the detonator rather than the bomb itself.” 
   
   A fossil of a trilobite, a horsecrab-like creature that thrived in the seas for hundreds of millions of years before becoming one of many kinds of animals wiped out in a mass extinction that befell the planet 252 million years ago, is shown in this handout photo provided by the University of Chicago March 31, 2014. REUTERS/Dan Dry/University of Chicago/Handout via Reuters 
   
   “As small as an individual microorganism is, their sheer abundance and ubiquity make for a huge cumulative impact. On a geochemical level, they really do run the planet,” he said. 
   
   The Permian mass extinction unfolded during tens of thousands of years and was not the sudden die-off that an asteroid impact might cause, the researchers said. 
   
   The most famous of Earth’s mass extinctions occurred 65 million years ago when an asteroid impact wiped out the dinosaurs that ruled the land and many marine species. There also were huge die-offs 440 million years ago, 365 million years ago and 200 million years ago. ||||| Climate-changing microbes may have caused the biggest mass extinction in history 252m years ago, scientists believe. 
   
   Volcanic eruptions had previously been blamed for the sudden loss of 90% of all species on Earth at the end of the Permian era. But new research suggests volcanoes only played a bit part in the catastrophe. 
   
   The chief perpetrators appear to have been a microscopic methane-producing life form called Methanosarcina that bloomed explosively in the oceans. The enormous quantities of methane, a potent greenhouse gas, generated by the single-celled organism are thought to have sent temperatures soaring and acidified the seas. Unable to adapt quickly enough, countless species vanished from the Earth. 
   
   Analysis of geological carbon deposits reveals a significant boost in levels of carbon-containing gases – either carbon dioxide or methane – at the time of the mass extinction. But volcanic eruptions alone could never have produced the amount of carbon laid down in rock sediments during this period, the researchers claim. 
   
   "A rapid initial injection of carbon dioxide from a volcano would be followed by a gradual decrease," said US scientist Dr Gregory Fournier from the Massachusetts Institute of Technology (MIT). "Instead, we see the opposite: a rapid, continuing increase. 
   
   "That suggests a microbial expansion. The growth of microbial populations is among the few phenomena capable of increasing carbon production exponentially, or even faster." 
   
   A timely combination of two factors may have sent Methanosarcina into overdrive, according to the findings reported in the journal Proceedings of the National Academy of Sciences. First, a genetic change allowed it to become a major producer of methane from accumulations of carbon dioxide in the oceans. Second, a surge in volcanic activity led to a sudden influx of nickel, a vital nutrient that helped the microbes proliferate. 
   
   • The picture caption was amended on 1 April 2014 because the original called Methanosarcina a bacterium. This has been corrected. ||||| The worst time to be alive in Earth's history is absolutely the end-Permian, about 250 million years ago. It is the period when the greatest-ever extinction took place, killing 97 percent of all species. The event was so severe it has been called The Great Dying. 
   
   The end-Permian extinction has generally been blamed on massive volcanic eruptions that took place at the same time. But now in a new analysis, researchers at the Massachusetts Institute of Technology argue that the mass extinction event may have been instigated by microbes. These microbes led to a perturbation of the carbon cycle that caused environmental shocks, such as global warming and ocean acidification. The shocks wiped out species in great numbers over a period of tens of thousands of years—a blip on geological scales. 
   
   The end-Permian extinction, which took place about 250 million years ago, is the most severe of five known mass extinction events. It killed off the last of the trilobites—a hardy marine species that survived two previous mass extinctions. While land plants survived, almost all forests disappeared. Worst of all, it is the only known extinction event where even insects weren't spared. 
   
   For an event of this size to take place, a lot of things would have to go wrong. At the time the world was made up of a single supercontinent called Pangea. This large landmass, by altering the dynamics of how carbon is cycled with subducting plates, may have pushed global temperatures to the highest they had ever been. 
   
   Over the course of about a million years, huge eruptions in Siberia spewed basalts that cover an area that was about seven times the size of France. This may have pushed the environment past a tipping point by sending even more carbon dioxide into the atmosphere. That would have caused the oceans to acidify, killing more marine life, and heat up, releasing frozen methane. The upshot of all this would have been a "runaway" climate that kept heating up and removing more oxygen from the environment. 
   
   A mighty microbe 
   
   But Daniel Rothman of MIT thinks that the numbers don't add up. "The changes in the carbon cycle globally are difficult to reconcile with only volcanic activity in Siberia," he said. His calculations, just published in the PNAS, were hinting that something else must have caused the runaway event. One hypothesis was that microbial life may have been responsible for that. 
   
   "This hypothesis is not as outrageous as it seems. After all, about 2.4 billion years ago, it was microbes in the form of cyanobacteria that gave our atmosphere all of its oxygen," Rothman added. That period, called the Great Oxygenation Event, also killed most organisms that were adapted to the lack of oxygen and began one of the longest cold periods in Earth’s history. So microbes can certainly have global impact. 
   
   With colleagues at MIT, Rothman looked at the evolutionary history of Earth and spotted the origin of a particular type of microbe that occurred around the time of the Great Dying. That microbe, called Methanosarcina, had the ability to digest organic matter to produce methane. (Molecular biologists at MIT have shown that Methanosarcina evolved this ability thanks to the transfer of a single gene from the Clostridia class of bacteria.) 
   
   Rothman knew that the chemical process involved in creating the methane relied on the metal nickel. (One of the enzymes the microbes use relies on it as a co-factor.) He went looking for evidence that Methanosarcina was thriving at the time in the sedimentary layer of the Meishan region of China. If the environment at that time had any more nickel than normal, then the sediments would hold the record of it. 
   
   Rothman chose the Meishan region to look for nickel because it is a particularly well-studied region. Its sedimentary layers have been used to mark and standardize different periods of Earth's geological history, and they span the period of the Great Dying. 
   
   The search was successful; there was indeed a higher amount of nickel in the sediments deposited during that period. Methanosarcina would not just have been effective at creating methane—they would have flourished. 
   
   The nickel, Rothman suggests, would have been added to the oceans, where Methanosarcina lived and grew, by the continuous volcanic activity occurring in Siberia. The growing amount of nickel, transported globally by ocean currents, would have allowed more Methanosarcina to convert organic matter into methane, which would be converted to carbon dioxide through reactions with oxygen. This would mean increased global temperatures and acidification of the oceans; the latter would have combined with the loss of oxygen (used up in creating the CO2) to accelerate the extinction in the oceans. And the dead organisms would have provided Methanosarcina with more organic matter to digest. 
   
   In short, a microbial innovation may have tipped over the balance to cause the Great Dying. 
   
   Marc Reichow at the University of Leicester remains skeptical of these results. He argues that there is no evidence that the increased nickel came from Siberian volcanoes. "This is an interesting hypothesis, but I think that Great Dying was the doing of many 'kill mechanisms' rather than just a single mechanism suggested here," Reichow said. Rothman agrees that current data cannot identify the source of the nickel. 
   
   There is also doubt over the exact period in which Methanosarcina actually evolved. Current techniques for estimating its origins based on DNA sequence differences have a huge error margin, which means it could have been well before or after the Great Dying. 
   
   Rothman concedes that there are limitations. "We believe that volcanism on its own could not have caused this extinction event. Instead, what we have done is broadened the conversation by suggesting that it is possible that microbes may have caused it to happen. 
   
   "The implications for today are that there are many ways in which natural fluctuations can happen in Earth’s carbon cycle. When studying the changes happening to the carbon cycle now, we should try to take into consideration as many of those as possible to make future predictions." 
   
   PNAS, 2014. DOI: 10.1073/pnas.1318106111 (About DOIs). 
   
   The article was originally published on The Conversation.
target: – Name your favorite culprit for the mass extinction that wiped out nearly every life form on Earth 250 million years ago. A spectacular asteroid, perhaps? Massive volcanic eruptions? Both are popular theories, but a new study encourages sleuths of the Permian era to think much, much smaller, reports the Guardian. As in microscopically smaller. MIT scientists propose that a microbe called Methanosarcina proliferated in the oceans, disgorging huge amounts of methane into the atmosphere and making life in the water and on land all but impossible for most species. "In short, a microbial innovation may have tipped over the balance to cause the Great Dying," explains Ars Technica. So what caused the microbes to explode in numbers? That's where those volcanoes may have played a role, though a lesser one than has been long surmised. Scientists think a flurry of eruptions in Siberia resulted in a huge increase in nickel, upon which Methanosarcina happens to thrive. An estimated 90% of marine species were wiped out in the changed atmosphere, along with 70% of land vertebrates. It took millions of years for both to recover, with the first dinosaurs showing up about 20 million years later, reports Reuters. (Scientists recently determined that the Permian mass extinction happened really, really quickly.)