When we think of extinction, a massive, apocalyptic and immediate event comes to mind. But the truth is that mass extinctions usually require thousands, and even hundreds of thousands of years. Until the catastrophic event that drove the last mass extinction 66 million years ago, which wiped out the dinosaurs, it took its time to annihilate.
Five great mass extinctions are counted in the history of life on Earth. Many scientists believe that a sixth is approaching, or even that it has already begun. And what do all mass extinctions have in common? Regarding the cause, a recent scientific study indicates that the second most severe mass extinction in the history of the Earth could have been caused by global warming. The discovery also suggests that all known mass extinctions may have been linked to a rapid rise in the planet’s temperature.
During the Paleozoic Era, the Ordovician period (after the Cambrian and before the Silurian) witnessed a great diversification of marine life. The explosion of life began during the so-called Cambrian explosion, in which life forms such as trilobites and other species of arthropods, ancestors of current insects, sponges, marine worms … and a variety of oceanic plants populated the seas. .
But this explosion of life ended abruptly with the Late Ordovician mass extinction, in a period that lasted between 500,000 and a million years. As cited in the scientific article, published by Geoscience World : about 85% of the species were eliminated in two stages. The first has been linked to the cooling and glaciation of Gondwana, the first supercontinent. The second wave, later, is attributed to global warming and anoxia (lack of oxygen in a tissue).
Scientists observed mercury peaks of this stage in a large and unknown ‘igneous province’ (zone of magmatic rocks) that has led to different interpretations of the extinction. According to the scientists, the data supports a scenario in which volcanic greenhouse gases caused warming that led to the expansion of a pre-existing oxygen minimum zone in deep water. This would have produced a collapse in the marine species on the ocean floor, and the first wave of extinctions.
For its part, renewed volcanism stimulated greater warming and anoxia (oxygen deficiency), thus driving the second wave. However, we still have a lot of data to know about what really motivated each of these extinctions.
Studying the causes of past mass extinctions can help to understand how phenomena such as volcanism and global warming are related to a phase of extinctions. “Instead of casting doubt on the warming-extinction nexus, this study now corroborates it: all mass extinctions on Earth are associated with global warming, ” the authors conclude.
References:
David PG Bond; Stephen E. Grasby. ‘Late Ordovician mass extinction caused by volcanism, warming, and anoxia, not cooling and glaciation’. Geology (2020) https://doi.org/10.1130/G47377
