83% of all genera died out approximately 250 million years ago, in the Permian-Triassic mass extinction event. This was the largest extinction event that has ever occurred on this planet. For the first time, a highly specific timeline of the event has been developed which will help researchers understand exactly how the extinction event came about. The study comes from Samuel Bowring from MIT and was published in the Proceedings of the National Academy of Science.
Mass extinctions occur when biodiversity of macroorganisms drops sharply in a relatively short period of time. These events make way for huge evolutionary changes as a variety of niches become vacant. This has happened five times throughout history, though the event at the end of the Permian saw an unprecedented amount of loss with 96% of marine life and 70% of terrestrial life getting wiped out.
In a 2011 study from the same lab, geological samples from a time known to mark the Permian-Triassic boundary were used to determine that the end-Permian event happened in under 200,000 years, which was too vague to make any definite conclusions about the cause. However, it did give them a good starting place to refine the search.
For the current study, the team collected samples from five ancient volcanic ash beds and compared the uranium isotopes. This allowed them to determine that the event lasted 60,000 years, give or take 48,000 years. That might sound like a large amount of wiggle room, but that is incredibly precise for dating a mass extinction which does not have clear boundaries. It was a huge shock that so many organisms could die out in what is, relatively, the blink of an eye and they needed to find out what caused it.
The leading theory for the cause of the end-Permian event is that extensive volcanic eruption from the Siberian Traps considerably raised carbon dioxide levels in the atmosphere which then dissolved into the ocean, slowly acidifying it and raising the temperature by as much as ten degrees. Conditions as extreme as this would have been tough on ocean life, as most marine species are very sensitive to even the slightest changes. Bowring’s team found evidence supporting this theory. They discovered that about 10,000 years prior to the die-off, the oceans spiked in carbon content, likely in response to increased carbon in the air.
The Siberian Traps are an expansive region in Russia represent the largest eruption in history, lasting for a million years from 251-250 million years ago. With such a precise timeline in place, geologists will now be able to take more samples from the Siberian Traps and find if certain chemicals, like carbon dioxide, align with the time period and in the quantities necessary to spark such a dramatic change in such a short amount of time. If the volcanic activity of the Traps is responsible for the carbon spike, scientists will have to determine if the activity occurred naturally or if there was an outside force involved, such as an impact event.
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