One of these days "Kompyulenta" wrote that the mass extinctions (especially Permian) were due to physiological crisis: high levels of carbon dioxide in the atmosphere reduced the pH of the ocean and called anoxia. However, it says little about, Thuabout was happening on the planet and how long of events.
According to new data, the great extinction took less than 200 thousand years. It was accompanied by a very rapid changes in the atmospheric concentration of carbon dioxide.
Different methods yield approximately the same date: it happened about 250 million years ago. The spread is, and it is due to not only the errors, but also a different impact on different ecosystems factors causing extinction. The new study, which was led by Shuchzhun Shen of Nanjing Institute of Geology and Paleontology of China (PRC), was designed to determine the timesextinction by-frame analysis of 300 samples from 29 volcanic deposits in southern China. Together, these places are marine, transitional and land environment.
Determining the age of the uranium-lead method, used in this case, has a standard error of 60-120 thousand years. However, a large number of samples allowed to restrict the period of extinction of up to 200 thousand years. As a result, scientists have come to the conclusion that it has been a little over 252 million years ago.
Then, in order to find out what happened to the biosphere, the authors applied to the analysis of carbon isotope ratios 12C and 13C. Since the latter is heavier beings usually prefer the former.
The researchers divided the carbon cycle in two fractions. One of them represent carbonate deposits, which are derived from the body, they are built from its shell. They are not included in the metabolic cycle, and therefore directly reflect the level of CO2 in the atmosphere (which affects the amount of carbon dioxide dissolved in the ocean). Another source of the carbon cycle — organic carbon, which reflects, Thuabout happens to the body at the time.
Now, scientists have found that approximately 90 thousand years before the extinction concentration 13C in the atmosphere began to gradually decline. Then, just before the start of the mass extinction, there was a sudden drop in the level of this isotope, which lasted less than 20 thousand years. With the start of extinction followed the example of atmospheric carbon organic, indicating that the mass death of the plant.
Such synchronicity led authors suggest a causal relationship. But what led to the pumping atmosphere lighter isotope? Scientists believe that the gradual decline in the share of the heavy isotope indicates a large loss of the light isotope of the biological system, the growth of volcanic activity and (or) change rate of weathering.
In the end, a combination of factors led to a tipping point, when there was a sudden and large release of carbon of biological origin. The authors believe that the gradual warming caused by the earlier release of carbon dioxide, dry tropical forests, which are then burned. In addition, the warming could destabilize methane, which was kept in a solid form on the ocean floor. Whatever the reason, it has led to anoxia, which, in turn, helped to cause mass extinction.
There is some evidence in favor of a broad volcanic activity on the eve of the great extinction. In many studies, it is the carbon dioxide of volcanic origin plays the role of the main killers. This time, the experts pushed him into the background: in their view, the final, fatal blow was carbon dioxide from biological sources.