Most Mass Extinctions Have Been Due to Global Warming

Might the next one be caused by humans rather than volcanoes?

The largest mass extinction, about 250 million years ago, was likely caused by massive outpouring of magma in Siberia for about 60,000 years.

Nearly 20 extinction events in Earth’s natural history have been analyzed in a new study by David Bond from the University of Hull in the U.K. and Stephen Grasby from the University of Calgary in Canada. They found that most of the events seen in the geologic record, starting about 500 million years ago and extending until today, can be linked to periods of massive volcanic activity, which caused global warming of the atmosphere together with acidification and oxygen depletion in Earth’s oceans. Other associated kill mechanisms were acid rain, damage to the ozone layer, enhanced ultraviolet radiation, and toxic metal poisoning.

Sound familiar? All these kill mechanisms are also side effects of the human-induced climate change we’re seeing today. For a future geologist looking back at Earth’s natural record a few million years from now, things may look pretty much the same: a well-defined mass extinction event starting in the current human-dominated (or Anthropocene) era, as measured by a drop in biodiversity and indications of massive die-offs in the rock record.

Bond and Grasby find that four of the “Big Five” extinctions in Earth’s history can be related to large-scale volcanism. Interestingly, though, some of the largest magma outpourings were associated with only a small loss of biodiversity, meaning there must be some other factor determining how severe the effect on animals and plants will be. Perhaps the gas content of different kinds of volcanoes is critical, or the location where it happened, or the continental configuration at the time of the eruptions.

For one of the “Big Five” extinctions, there’s a more plausible explanation than volcanic activity: the K-T extinction event that spelled the end of the dinosaurs 65 million years ago, which is thought to have been caused by an asteroid impacting Earth. And even in this case, volcanic activity may have played a role.

Volcanoes, of course, indicate that we live on a dynamic, active planet. As long as Earth remains habitable, it will be volcanically active, and some of the eruptions will be very energetic. Now imagine one of these large-scale magmatic outpourings, with lots of gas venting, should occur at the same time human-made global warming is taking place. The result might be the largest mass extinction Earth has ever seen.

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