What Caused the First Mass Extinction 445 Million Years Ago? Global Warming, Suggest Scientists

As humans currently live through and accelerate what potentially is the sixth mass extinction, scientists may have finally figured out what caused the planet’s first mass extinction. In a study published last month in the science journal Geology, scientists have suggested that the extinction that took place around 445 million years ago was probably due to a culprit we grapple with even today: global warming. Well, that and volcanic eruptions and anoxia (loss of oxygen supply).

The first extinction happened in what is known as the Late Ordovician period and is said to have wiped out over 85 percent of all Ordovician species. It is believed that the extinction happened in several phases. The first phase has been linked to cooling and glaciation, while the second to warming and anoxia. Scientists believed that global glaciation reduced the amount of water available for marine life—the most common life-form existing on the planet back then. Then, when the planet heated up, the ice melted, causing the oxygen levels to drop. This drop is then what led to the wipe-out of the majority of marine-based life.

While it was believed that the late Ordovician mass extinction was the odd one out from the other mass extinctions due to its origins in cooling, the beliefs now seem to have been proven wrong by the scientists of this study—David Bond and Stephen Grasby. “The Ordovician one has always been a little bit of an oddball,” said Stephen Grasby to The New York Times. “This wasn’t an oddball cooling event. It joins the club as another ‘death by warming.’”

Their hypothesis supports an extinction scenario in which greenhouse gases, originating from volcanic bursts, caused warming, and that is what subsequently led to the extinction. Their findings don’t discount the glaciation at the time but suggest that the cooling was caused by global warming triggered by volcanic eruptions.

The scientists reached this conclusion after testing Ordovician rocks from southern Scotland that date back to the Late Ordovician period. With high heat, they were able to measure elements of large quantities of mercury that were emitted by the rocks—a telltale sign that these stones came from an Earth with a volcanic environment and deoxygenated waters.

These mass extinction findings can be vital to us as we accelerate towards the first human-caused mass extinction event.

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