Scientists Raise New Theory on Mass Extinction of Life 250 Million Years Ago

Chinese scientists have claimed that the mass extinction of living things some 250 million years ago didn't occur in two or three phases as previously thought, but all at once.

The new theory is of great significance to finding answers to the mystery of mass extinction, scientists said.

The US magazine Science Friday published the theory, raised by a research group led by Jin Yugan, a research fellow at Nanjing Institute of Geology and Paleontology affiliated with the Chinese Academy of Sciences, China's highest learning institution of natural sciences.

The unprecedented mass extinction 250 million years ago has long perplexed scientists. The extinction was responsible for the deaths of half of the marine life and one third of the onshore life killed in a total of six mass extinctions over the past 600 million years.

Traditionally, scientists believed that the mass extinction 250 million years ago was caused by the sinking sea level, which worsened environmental conditions and led to the mass destruction of life. They surmised that living things died in two or three separate disasters between 263 million and 251 million years ago.

However, Chinese scientists cast doubt on that theory after their discovery of abundant fossils in the 1970s at Meishan Mountain in Chengle County, east China's Zhejiang Province.

Using carbon dating technology, Jin's group believes that there was only one catastrophic event in that period.

Over the past several years, Jin and his colleagues have systematically studied 333 kinds of fossils in Meishan, determining that most of the fossils belonged to certain strata.

In these strata, carbon isotopes, an indicator of the extinction of life, decreased sharply. In addition, microspheres --evidence of volcanic eruption or extra-terrestrial impact -- were hundreds of times the level of other stratum.

Jin's group includes Wang Yue, Wang Wei, Shang Qinghua and Cao Changqun. Support has been lent by D. H. Erwin of the National Museum of Natural History with Smithsonian Institution of the United States.

The Chinese researchers believe its most likely that the mass extinction was caused by volcanic eruption or extra-terrestrial impacts, perhaps from meteorites.

Some 250 million years ago, catastrophes known as Siberian Trap volcanism devastated the earth. The mass extinction can be compared with the deaths of dinosaurs during the transition from the Mesozoic to Cenozoic eras 65 million years ago.

The extinction led to the transition from the Paleozoic to Mesozoic eras, in which ecosystems changed profoundly and new living species emerged.

The theory posited by Jin and his colleagues adds weight to the belief that disasters and the ability to survive are equally important to the evolution of living things, posing a new challenge to Charles Darwin's theory of evolution.



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