By analyzing rock samples unearthed in Oman, researchers have found that low oxygen and iron-rich waters delayed the recovery of life following mass extinction 252 million years ago
About 252 million years ago, a catastrophe event wiped out almost 96% of marine life and almost 70% of animal species living on the surface. The event, known as Permian–Triassic Extinction, is recognized as the worst mass extinction event in the history of the Earth.
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The oceans on Earth were so starved of the oxygen in the wake of the disaster that it took a long time for them to rebuild life again. Precisely, the recovery of life was delayed by an astonishing five million years.
Previous researches linked this delayed recovery of life not only to the lack of oxygen – a condition known as anoxia - but also to the high concentrations of hydrogen sulphide. But no-sayers argue that anoxia conditions at that time were not as simple as we think. There is no strong evidence available for the existence of high levels of sulphide concentrations in all the oceans around the world and they believe something else might have contributed to the delay rather than sulphide but they are unable to pinpoint that exact factor. So, the case of the recovery of life remains unsolved even today.
But now the pieces are starting to come together, thanks to a team of researchers led by University of Edinburgh. They have collected the samples of rocks from Oman existing around the time of mass extinction and analyzed their chemical properties.
By analyzing rock samples, researchers have been able to learn new details about the oceans and their chemistry after the occurrence of catastrophe event. They found that the oceans at that time lacked the oxygen but they didn’t have concentrations of sulphide. Instead, the waters were rich in iron.
Researchers suggest that the combination of low oxygen and high levels of iron have delayed the recovery of marine life following the Permian–Triassic Extinction event.
“We knew that lack of oxygen in the oceans played a key role in the extinction and recovery processes, but we are still discovering how exactly it was involved,” said lead researcher Dr Matthew Clarkson. “Our findings about the chemistry of the ocean at the time provide us with a clearer picture of how this complex process delayed the recovery of life for so long.”
Research also reveals that oxygen levels were not the same across the ocean. The depths of the oceans had very low levels of oxygen while the shallower water have just had enough oxygen to sustain diverse forms of marine life. But what triggered anoxic conditions in the oceans across the globe, it still remains unclear.
Co-author Professor Simon Poulton from University of Leeds says.“The neat point about this is that it shows just how critical an absence of oxygen, rather than the presence of toxic sulphide, was to the survival of animal life. We found that marine organisms were able to rapidly recolonise areas where oxygen became available."
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