Explain the mass extinction on Earth 250 million years ago

A new study suggests that toxic gases that destroy the ozone layer escaping from oceans may not be the cause of the world's largest mass extinction so far.

'Terrible death' occurred 251 million years ago, at the end of the Permian period, causing the Earth to lose about 90% of species living in the ocean and about 70% of terrestrial species. Scientists suspect the main reason is the high concentration of hydrogen sulfide and methane in the atmosphere of poisoning organisms and destroying the protective ozone layer.

According to David Beerling, co-author of the work, a biologist at the University of Sheffield, England, the 'The end of the Permian period, the climate is warmer, the CO2 in the air is higher than the present. Ocean circulation becomes extremely stagnant and the ocean becomes oxygen deficient. ' Under these conditions, ocean bacteria convert sulfur to produce hydrogen sulfide, a compound that accumulates in the ocean and then attacks the atmosphere.

'There is evidence that methane is released in large quantities at the end of the Permian period, either from warm oceans or from coal mines heated by volcanic activities at this time.' But the discovery of these chemicals could not be enough to damage the ozone layer, making scientists hunt for another answer to the mysterious cause of this biological disaster.

Self-cleaning system

Beerling and colleagues built Permian computer and ocean simulations of the ocean to predict what could happen when the levels of hydrogen sulfide and methane increased. 'We found interesting things happening with substances in the ozone layer, but could not find any evidence that hydrogen sulfide and methane caused the ozone layer to collapse.'

Previous calculations also used global standard figures - surveying altitudes only, not including latitudes - thus ignoring the effects of hydroxyl radicals.'These chemicals are generated mainly in the tropics and oxygenation (thus neutralizing) the waste that destroys the ozone layer.' Even when hydrogen sulfide levels are increased at very high levels in two-dimensional samples, hydroxyl radicals neutralize them and prevent ozone collapse.

This work is in Nature Geoscience.

Not too cruel

Lee Kump, a geochemist at Pennsylvania State University at University Park, participated in previous studies predicting dangerous levels of hydrogen sulfide at the end of the Permian period.
The conditions created by previous calculations ' may have wiped out life on Earth and did not allow anything to survive. No creature can escape it. '

Kump said he was very interested in the new work because it mitigated the devastating consequences of an oxygen-deficient ocean and helped explain how some organisms still managed to stay abreast. But he also warned that these chemicals may still play a fundamental role in this mass extinction. Kump said 'The hydrogen sulfide content may not be enough to destroy the ozone layer. However, new calculations still show a significant increase. We don't know what the consequences of that for terrestrial life. ' Beerling said, 'Hydrogen sulfide poisoning in the ocean is still a possibility. Our calculations do not exclude that. '

Earth's map about 250 million years ago, at the time of mass extinction, wiped out much of life on Earth. Scientists have been responsible for hydrogen sulfide compounds released from oceans with low oxygen content. But a new study finds that the amount of hydrogen sulfide may not be enough to destroy the ozone layer, making scientists have to study other explanations for this biological disaster. (Photo: Nicolle Rager)

Harmful effects of ultraviolet rays

Scientists still believe that the ozone layer still suffers a form of devastation during the Permian period but is caused by another chemical group. For example, scientists have discovered altered plant pollen. This demonstrates that the ozone layer is damaged, causing ultraviolet rays to destroy the Earth's surface.

According to Beerling 'We recorded a sharp increase in four valence elements - strange mutant spores - in the late Permian rock around the world.' Kump adds, 'This new work proves quite clearly that the collapse of the ozone layer may need more than just the increase in hydrogen sulfide in the atmosphere.' Another theory is about large-scale volcanic activities known as Siberian Rock, releasing hydrochloric acid and organic halides into the atmosphere. Beerling said that 'Volcanic activity is even the most likely explanation for extinction because we have excluded other causes.'

Paul Wignall, a paleontologist at the University of Leeds, UK said that 'Now this work has proved that hydrogen sulfide and methane are not suitable, we are back to the beginning and look for other mechanisms. 'However, he also thinks that the hypothesis about volcanoes is only a guess. 'The theory of organic halogen pollutants may be true, but there is no evidence to support it.'

Earth's map about 250 million years ago, at the time of mass extinction, wiped out much of life on Earth. Scientists have been responsible for hydrogen sulfide compounds released from oceans with low oxygen content. But a new study finds that the amount of hydrogen sulfide may not be enough to destroy the ozone layer, making scientists have to study other explanations for this biological disaster.