US, WASHINGTON (ORDO NEWS) — At the beginning of the late Ordovician period, about 450 million years ago, the world was completely different than today or even in the era of dinosaurs. So, living organisms lived mainly in the oceans, and plants were just beginning to appear on land.
Most of the modern continents were combined into one Gondwana supercontinent, including Africa, South America, Antarctica, Australia, New Zealand, as well as Arabia, Madagascar and Hindustan and formed at the end of the Precambrian after the split of the supercontinent Rodinia.
The early Ruddan century of the Silurian period, which began about 444 million years ago, is associated with the Ordovician-Silurian glaciation – one of the three great Paleozoic glaciations – and the mass extinction at the border of the Ordovician and Silurian, during which about 85% of species and 60% of genera of marine invertebrates died animals. It is believed that the first phase of this extinction was associated with global cooling and affected mainly deep-sea species.
The second phase, according to a group of scientists from the United States, was due to a sharp anoxia (oxygen depletion) of the ancient oceans and a drop (almost to zero) in the concentration of carbon dioxide in the atmosphere of the planet. According to a new work published in the journal Nature Communications , such anoxic conditions have been observed for over three million years and have affected all marine life.
The authors of the study built a model that included previously published data on ancient deposits containing isotopes of metals, such as uranium and molybdenum, undergoing various chemical reactions during anoxia. In addition, isotopic samples of fossils from the end of the Ordovician, found in the deposits of the Hirnant layer in Libya, were studied – it is assumed that most of the flora and fauna died then.
As a result, scientists confirmed their assumptions that the second stage of mass extinction at the border of the Ordovician and Silurian periods is associated with a long and serious anoxic event on the ocean floor. Despite the fact that the reasons for the sharp decrease in oxygen concentration both in the ancient oceans and in the Earth’s atmosphere are not yet clear, such conditions definitely led to the death of multicellular marine life.
“Thanks to the constructed model, we can confidently say that the second phase of the Ordovician extinction was accompanied by a sharp decrease in oxygen concentration, including at a depth. For most representatives of oceanic multicellular life, the border between the last Ordovician era and the beginning of the Silurian was a really bad time,” said Eric Sperling, an associate professor at Stanford University (USA).
Researchers note that their findings can also help in studying the present and future of our planet. “In fact, scientists have big problems modeling oxygenation in the modern oceans,” adds Sperling. “By expanding our understanding of how the oceans behaved in the past, we could better understand the oceans today.”
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