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mass extinctions Geologists and paleontologists study the history of life on Earth through detailed examination of that record as preserved in sedimentary rock layers laid down one upon the other. For
Solar radiation hundreds of years paleontologists have recognized that many organisms are found in a series of layers, and then suddenly disappear at a certain horizon never to reappear in the succeeding progressively younger layers. These disappearances have been interpreted to mark extinctions of the organisms from the biosphere. After hundreds of years of work, many of these rock layers have been dated by using radioactive decay dating techniques on volcanic rocks in the sequences, and many of these sedimentary rock sequences have been correlated with each other on a global scale. some are associated with other deposits along the layers, indicating unusual concentrations of the metal iridium, carbon from massive fires, and other impact-related features such as tektites and tsunami deposits.
one of the more important findings resulting from such detailed studies is that the rock record preserves evidence of several extinction events that have occurred simultaneously on a global scale. Furthermore, these events do not just affect thousands or hundreds of thousand of members of a species, but they have wiped out many species and families each containing millions or billions of individuals.
Continue reading here: Processes That Drive Evolution And ExTinction
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