We finally know what killed marine life in the deadliest mass extinction in history


About 252 million years ago, Earth suffered catastrophic devastation – an event of extinction so severe that it destroyed almost all life on Earth.

Up to 70 percent of all terrestrial vertebrate species were killed and 96 percent of all marine species, including the famous trilobite, which had survived two other mass extinction events.

It is called the Permian-Triassic Extinction Event, also known as Great Death, and, as far as we know, was the most calamitous event in Earth's history.

It is widely accepted that climate change is to blame – more specifically that long-term volcanic activity in Siberia expelled so much material into the atmosphere that it wrapped the world in a mantle of ashes for a million years, simultaneously blocking sunlight, ozone, falling acid rain and raising temperatures.

Scientists have now demonstrated what has obliterated marine life: rising temperatures have accelerated the metabolism of ocean creatures, increasing their oxygen needs and, at the same time, depleting the oceans of oxygen.

The animals literally choked.

And we're experiencing similar atmospheric warming again today – just a lot faster than Great Dying, which showed warning signs for 700,000 years before the event itself.

"This is the first time," said oceanographer Justin Penn of the University of Washington, "that we have made a mechanistic prediction about what caused the extinction that can be directly tested with the fossil record, which allows us to make predictions about the causes of extinction in the future ".

The team performed a computer simulation of the changes the Earth passed during the Great Death. Before the volcanic eruptions of Siberia, temperatures and oxygen levels were similar to what they are today, which gave them a good basis to work.

They then raised the greenhouse gases in the atmosphere of the model to mimic the conditions after the eruption, which raised the sea surface temperature to about 11 degrees Celsius (20 degrees Fahrenheit).

Of course, this resulted in an oxygen depletion of about 76% – and about 40% of the seabed, especially at great depths, was totally depleted of oxygen.

To observe how this would affect marine life, the team connected oxygen requirements data from 61 modern species in the simulation. It was a disaster.

"Very few marine organisms remained in the same habitats as they lived – either fled or died," said oceanographer Curtis Deutsch of the University of Washington.

The most affected were creatures more sensitive to oxygen, with the most pronounced devastation in high latitudes, far from the equator. When the team compared its result to the fossil record, it confirmed their findings.

This is because animals that live in warmer waters around the equator can migrate to higher latitudes where they will find habitats similar to those they have just left. But animals that already live in higher latitudes have nowhere else to go.

In total, the researchers found that this represented more than 50% of Great Dying's loss of marine diversity. The rest was probably caused by other factors, such as CO acidification2 of Siberian traps, and a marked decline in plant life caused by dilute ozone.

We should be sitting and paying attention to this, the researchers said. This temperature increase of 11 degrees Celsius took a few thousand years, more or less.

Since 1880, Earth's average temperature has risen by 0.8 degrees Celsius (1.4 Fahrenheit) – and two-thirds of that increase has occurred since 1975. And warming of Earth's oceans is accelerating.

"Under a scenario of emissions as usual, by 2100 the warm up in the upper ocean will have reached 20% of the warming at the end of the Permian, and by the year 2300 will reach between 35 and 50%," Penn said.

"This study highlights the potential for a mass extinction stemming from a similar mechanism under anthropogenic climate change."

Remember this.

The team's research was published in the journal Science.


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