They also found traces of volcanic ash. After each volcanic eruption, the ash would be deposited and stored in the ground. According to Shen, the volcanic ash often contained zircon and other minerals. These minerals are very stable and can withstand temperatures as high as 3,000 degrees Centigrade. They are common in acid igneous rocks. Their composition can be used to determine the exact time of a volcanic eruption.

Paleontologists collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections. High-precision zircon U-Pb dating reveals that the extinction peak occurred just before 252.28 million years ago minus or plus 80,000 million years ago.

It was the first time the scientific community determined the exact time of the mass destruction.

"The 25th layer of the geological profile in Meishan Mountain was crucial. It was the exact layer of volcanic ash which dated back 252.28 million years," said Shen.

"After fossil comparison, volcanic ash age analysis, as well as other scientific means, we got the exact time of the mass extinction. Our result shortened the previous estimated period of the mass extinction to 200,000 years. Thus we proved the mass destruction was absolutely not a slow process but a quick and short one," said Shen.

During the process of collecting evidence and doing research, the team noticed an extraordinary change in the carbon isotope. The carbon isotope ratio is an effective means of determining the source of the carbon dioxide in the atmosphere. The team discovered within the short period of 10,000 to 20,000 years at end-Permian period, the Earth's inorganic carbon isotopic concentrations witnessed a sharp fluctuation.

"Such a dramatic fluctuation means a quick change in the percentage of carbon dioxide in the atmosphere. It indicates the advent of a disaster for global biodiversity," said Shen.

Reasoning

As Shen saw it, at the end-Permian period, underground magma became active. Its large-scale movement led to the release of methane and volcanic eruptions.

As a result, carbon dioxide increased quickly and the greenhouse effect intensified. The lack of oxygen in the sea led to a mass extinction of marine life. In the meantime, it quickly got warm and dry on the Earth. This caused widespread wildfires, which eventually triggered the catastrophic extinction.

This was proved by the plant fossils. The team found a lot of evidence of burning trees in the fossils. The continuous burning of trees led to vast disappearance of forests. And the soil protection system collapsed.

Before Shen's discovery, it was generally agreed among academics that the process of mass extinction at the end-Permian period began with the sea and then spread to the land. But Shen's research showed the sea and the land suffered from the quick and devastating hit at almost the same time.

The release of methane, volcanic eruptions, increase in carbon dioxide and greenhouse effect had a synchronous impact on the marine and terrestrial ecosystems synchronously, said Shen.

This was also proved by the fossils. The team found fossils of gigantopterides, a representative rainforest plant, in the equatorial regions. They showed rainforest plants disappeared simultaneously with marine life. It took the Earth more than 5 million years to recover, said Wang Jun, another researcher with the NIGP.

"The mass extinction at end-Permian told us the ecosystem's reactions to the environmental degradation may be long-term, but once the pressure on the environment goes beyond the capacity of the ecosystem, it can collapse in a very short time," said Shen.

"Human beings therefore should cherish the current environment," he said.

Email us at: tangyuankai@bjreview.com