Two oxidation phenomena in ancient oceans explain the spread of complex life forms

According to a new study, increased oxygen and oxidation rates in deep waters around 635 to 551 million years ago could affect the increase and spread of the first complex life forms. .

Today we use oxygen with many purposes. But oxygen only appeared on Earth's atmosphere 2.5 billion years ago, and 600 million years ago, atmospheric oxygen only accounted for a very small percentage of what it is today. For a long time, geologists and evolutionary biologists have studied the rise of the gases needed for respiration, as well as the subsequent oxidation process in deep-sea areas closely related to the evolution of modern biological systems.

To demonstrate the link between biological evolution and environmental change, the international team of scientists at Virginia Tech, University of Maryland, Nevada University in Las Vegas and the Chinese Academy of Sciences studied saving geochemical changes and the distribution of sediments from 635 to 551 million years ago were kept at Doushantuo Formation (Yangtze Pass area - southern China).

According to Kathleen A. McFadden, a doctor of biology at Virginia University of Technology and a lead author in PNAS, millions of years ago the Yangtze Pass area was the sea. In order to determine when the level of oxygen reached enough for marine life, researchers have asked the question: 'What geochemical evidence has been recorded on the stones? ? ' (According to Shuhai Xiao - associate professor of geology at Virginia University of Technology).

In the picture (a wide view of about 0.15 millimeters) is a fossilized cell of a fully preserved human nucleus at the Doushantuo Formation - South China area.Analysis of geochemical data shows that the very early diversification of eukaryotic cells may be related to the periodic oxidation that takes place in the oceans in the Ediacara period.(Photo: Shuhai Xiao)

Scientists hypothesize that a lot of organic carbon exists in the ocean when the oxygen ratio is still low . When oxygen levels rise, some of the organic carbon is oxidized to inorganic carbon - some of which is preserved in the form of calcium carbonate on the rocks. Ganging Jiang - assistant professor of geology at the University of Nevada in Las Vegas and co-author of the study, said: 'We have identified carbon isotopes of both organic carbon and inorganic carbon in layers. ancient soil and rock from which to deduce oxidation phenomena '.

The sediments at Three Gorges Dam have a lifespan of millions of years. McFadden said: 'We examine each layer of rock, measure and determine its properties; then every few feet we took a small piece of rock '. She collected 200 soil and rock samples, they were sent to 3 different laboratories. "

The researchers washed and crushed the samples into powder, then reacted with the acid to release carbon dioxide from carbonate. The residue is burned to get carbon dioxide from organic material. McFadden said: 'We use spectroscopy to measure the amount of carbon dioxide released; from that we know the ratio of organic carbon isotopes and carbonates found in rock samples'.

'The excess of carbon 12 isotopes and carbon 13 without decay over time gives us a picture of the environmental processes involved in nature at different times recorded. in rock layers'.

The stratigraphic pattern of carbon isotopes has shown researchers that the ocean previously had a severe lack of oxygen when animals were not present; But it was provided with oxygen from two separate events.

McFadden said: ' The first event seems to have little impact on the vast organic carbon reserves deep in the ocean, but also has significant effects on microscopic life forms. The second event occurred about 550 million years ago; however, it causes a decrease in organic carbon reserves. This suggests that the ocean began to be deeply oxidized just before evolution occurred as well as the diverse presence of the first animals on earth . '

McFadden continued: 'Doushantuo Formation keeps precious fossils. We can therefore study major fossil groups, when they appear and when they become extinct, and see the relationship between oxidation phenomena and organisms' groups.

Alan J.Kafman, co-author of the University of Maryland study, said: 'Research has supported the notion that life and the environment have evolved together in this intense development of the earth.'

The researchers analyzed fossil samples taken from Doushantuo Formation (from microscopic life forms that appeared 635 million years ago to algae that appeared 551 million years ago). Looking at data from four locations with similar isotope records, scientists believe that the first oxidation phenomenon makes microscopic organisms grow, some of which are thought to be grow into the first animals. The second oxidation event occurred simultaneously with the dizzying increase of complex algae species . McFadden said: 'Both oxidation events occur at the same time as the increased diversity of the fossil group at the Doushantuo basin with the number of species almost doubling.'

Following the second oxidation event, 550 to 542 million years ago, is the global increase of Ediacara's biotic (microscopic forms of life with complex structures) - this event has recently been placed named Avalon Boom. That is the time we have the first burrowing animals along with mineralized animals in fossil records. Mineralized animals are the first organisms with external bones, or apricot.

However, the motivation of these two oxidation phenomena has not been clarified. McFadden said: 'The phenomena found in the ocean are related to atmospheric oxygen reacting to underground sediments. Soil and rock undergoing sun and rain can release certain soluble ions (eg sulfate) and then wash them into rivers and streams. These ions are brought to the ocean again, where they can be used by bacteria to oxidize the organic carbon in the deep ocean. '

Ediacara's " Oxidation and biochemical evolution phenomenon " was written by Kathleen A. McFadden, co-author: Jing Huang and Xuelei Chu of the Geography and Geophysical Institute - Chinese Science Student, Ganqing Jiang, Alan J. Kaufman, Chuanming Zhou and Xunlai Yan of the Nanjing Institute of Geography and paleontology - Chinese Academy of Sciences, finally Shuhai Xiao, refer to the article at http://www.pnas.org / cgi / content / abstract / 0708336105v1 The article will be published on the March 4 issue (number 9, part 105 - page 3197-3202).

This collaborative study is funded by NSF's Biological and Geological Stock Program, NASA's Extraterrestrial Biology Program, China National Natural Science Foundation, Virginia Institute of Applied Technology and Critical Science, and the Foundation. Earth evolution and some other funds funded.