The extinction of the end of the Permian, which wiped out most species of the Earth, was instantaneous in geological time

According to a new study conducted by MIT scientists in China and elsewhere, the worst extinction in Earth's history has had few warning signs.

The mass extinction of the late Permian, which occurred 251.9 million years ago, killed over 96% of the world's marine species and 70% of its earthly life – world annihilation that marked the end of the Permian.

The new study, published today in the GSA Newsletter, reports that during the 30,000 or so years that preceded the extinction of the end of the Permian, there is no geological evidence of the disappearance of species. The researchers also found no sign of large variations in ocean temperature or dramatic fluxes of carbon dioxide in the atmosphere. When oceanic and terrestrial species became extinct, they did so en masse, over a geologically instantaneous period.

"We can say with certainty that there was no initial extinction," says co-author of the study, Jahandar Ramezani, a researcher at the Department of Earth Sciences, the atmosphere and planets of MIT. "A vibrant marine ecosystem continued until the end of the Permian, and then life disappears, and the great result of this document is that we do not see any warning signs of extinction. it's gone very quickly geologically. "

Among the co-authors of Ramezani are Samuel Bowring, professor of geology at MIT, as well as scientists from the Chinese Academy of Sciences, the National Museum of Natural History and the University of Calgary.

Find missing parts

For more than two decades, scientists have been trying to determine the timing and duration of the Permian mass extinction to better understand its possible causes. The greatest attention has been devoted to the well-preserved layers of fossil-rich rocks in eastern China, in a place known to geologists as the Meishan section. Scientists have determined that this section of sedimentary rocks was deposited in an ancient ocean basin just before and after the end of the Permian. As such, the Meishan section is supposed to preserve the signs of life and climate of the Earth before the calamitous event.

"However, the Meishan section is deposited in deep water and is highly condensed," says Shu Shen Shonghong of the Nanjing Institute of Geology and Paleontology in China, who led the study. . "The rock record may be incomplete." The full extinction range at Meishan includes only 30 centimeters of old sedimentary layers, and it is likely that there have been periods in this particular ocean environment when sediments do not occur. are not installed, creating "empty filing" not been registered.

In 1994, Shen took Bowring, along with paleobiologist Doug Erwin, now a Paleozoic invertebrate curator at the National Museum of Natural History and co-author of the paper, in search of a more extinctive record. complete in Penglaitan, a much less studied section of rocks in Guangxi Province in southern China. The Penglaitan section is what geologists consider "very extensive". Compared to 30 centimeters of Meishan sediments, the Penglaitan sedimentary layers constitute a much larger ensemble of 27 meters that were deposited during the same period, just before the main extinction occurred.

"It comes from a different part of the former ocean basin, closer to the mainland, where we can find coral reefs and much more sedimentation and biological activity," explains Ramezani. "So we can see a lot more, as in what is happening in the environment and in life, in this same period."

The researchers carefully collected and analyzed samples from several layers of the Penglaitan section, including ash samples deposited by volcanic activity while the seabed was crushed slowly under the continental crust. These ashes contain zircons, tiny grains of minerals containing uranium and lead, which researchers can measure to determine the age of the zircon and the ash bed from which it is derived.

Ramezani and his colleagues used this geochronology technique, developed largely by Bowring, to determine with great accuracy the age of several layers of ash throughout the Penglaitan section. From their analysis, they were able to determine that the extinction of the Permian end occurred suddenly, about 252 million years ago, or 31,000 years ago.

"A punch"

The team also analyzed sedimentary layers of fossils, as well as isotopes of oxygen and carbon, to better understand the temperature of the ocean and the state of its carbon cycle at the time of deposit. sediments. According to the fossil record, they expected to see disappearing waves of species before the end of the extinction period. Likewise, they have anticipated major changes in the temperature and chemistry of the oceans, which would signal imminent disaster.

"We thought we would see a gradual decline in the diversity of life forms or, for example, some species known to be less resilient than others, we would expect them to disappear early, but we do not see this , "Said Ramezani. "The disappearances are very random and do not conform to any physiological process or environmental effect, which makes us believe that the changes we observe before the event horizon do not really reflect extinction."

For example, researchers found signs that the ocean temperature was 30 to 35 degrees Celsius from the base to the 27-meter interval – a period of about 30,000 years before the main extinction. This temperature variation is not, however, very significant compared to a much greater warming that occurred after the disappearance of most species.

"The big changes in temperature occur just after extinction, when the ocean becomes really hot and uncomfortable," said Ramezani. "We can therefore exclude that the temperature of the ocean has been a factor of disappearance."

So, what could have caused the sudden and global wipeout? The main hypothesis is that the extinction of the end of the Permian was caused by massive volcanic eruptions that dumped more than 4 million cubic kilometers of lava on what is now called 39. traps of Siberia, Siberia, Russia. Such huge and lasting eruptions have probably released huge amounts of sulfur dioxide and carbon dioxide into the air, heating the atmosphere and acidifying the oceans.

Earlier work by Bowring and his former graduate student, Seth Burgess, determined that the timing of the Siberian trap eruptions coincided with the end of the Permian. But according to new data from the Penglaitan section team, even though global volcanic activity has dominated the last 400,000 years of the Permian, there does not seem to be any dramatic disappearance of species marines or significant changes in the temperature of the ocean. and atmospheric carbon in the 30,000 years that preceded the main extinction.

"We can say that there was significant volcanic activity before and after extinction, which could have caused environmental stress and ecological instability." But the global ecological collapse came with a blow Suddenly, and we can not see its extinction, says Ramezani. "The key to this article is the abrupt disappearance. Any assumption that extinction would have been caused by gradual environmental changes at the end of the Permian – all these slow processes we can exclude. we always try to understand what it meant and what was the cause. "

"This study adds a lot to the growing evidence that the Earth's leading extinction events occur on very short time scales, geologically speaking," says Jonathan Payne, professor of geology and biology at Stanford University. "It is even possible that the main impetus for the extinction of the Permian has occurred in a few centuries.If it reflects an environmental tipping point in a longer interval of permanent environmental changes, it should concern us happening in the world around of us right now. "

Explore more:
According to a study, the extinction of the end of the Permian has occurred in 60,000 years, much faster than previous estimates

More information:
Shu-Zhong Shen et al. A sudden disappearance of the end of the Permian in South China, GSA Newsletter (2018). DOI: 10.1130 / B31909.1