NEW DELHI, Nov 9: Earth has witnessed five major mass extinction events and the geologists have found that the first such event occurred near the end of the Ediacaran Period some 550 million years ago which was caused by major decrease in global oxygen availability resulting in loss of majority of animal lives.
After this, earth has gone through five other major mass extinction events which included Ordovician-Silurian Extinction (440 million years ago), the late Devonian Extinction (370 million years ago), the Permian-Triassic Extinction (250 million years ago), the Triassic-Jurassic Extinction (200 million years ago), and the Cretaceous-Paleogene Extinction (65 million years ago).
The researchers found that the extinction event included the loss of many different types of animals, however, those whose body plans and behaviours indicate that they relied on significant amounts of oxygen seem to have been hit particularly hard.
The study has been published in the Proceedings of the National Academy of Sciences which states that mass extinctions are well recognised as significant steps in the evolutionary trajectory of life on this planet. “We find support for decreased global oxygen availability as the mechanism responsible for this extinction,” the paper read.
Researchers studied fossil imprints in rocks to understand how the creatures that perished in this extinction event would have looked. They said that before this extinction the fossils they find don’t often fit into the ways we classify animals today. “Essentially, this extinction may have helped pave the way for the evolution of animals as we know them.”
Led by Scott Evans, a postdoctoral researcher in the Department of Geosciences, part of the Virginia Tech College of Science, the researchers demonstrated that environmental changes, such as global warming and deoxygenation events, can lead to massive extinction of animals and profound disruption and reorganization of the ecosystem.
“This has been demonstrated repeatedly in the study of Earth’s history, including this work on the first extinction documented in the fossil record. This study thus informs us about the long-term impact of current environmental changes on the biosphere.” co-author of the study Shuhai Xiao said.
While researchers are yet to fully understand the reason behind the sudden drop in oxygen levels of the planet that caused the first mass extinction event, they speculate it could be a combination of a number of events happening during the period.
“It could be any number and combination of volcanic eruptions, tectonic plate motion, an asteroid impact, etc., but what we see is that the animals that go extinct seem to be responding to decreased global oxygen availability,” Evans said.
The study comes amid reports of loss of oxygen availability affecting the world’s fresh waters. The cause behind this oxygen loss is the warming of waters brought on by climate change and excess pollutant runoff from land use. The rising temperature of sea water diminishes fresh water’s capacity to hold oxygen.
“Our study shows that, as with all other mass extinctions in Earth’s past, this new, first mass extinction of animals was caused by major climate change — another in a long list of cautionary tales demonstrating the dangers of our current climate crisis for animal life,” Evans added.
(Manas Dasgupta)