In a new investigation, published in the journal Nature Communications, Clarkson has unravelled the factors behind the planet's slow comeback - something that could help us better understand how environmental change can have disastrous consequences for life.
While previous research linked the event and recovery to the presence of anoxic waters that also contained high levels of harmful sulphide compounds, the study authors say anoxic conditions at the time were more complex, and that this toxic, sulphide-rich state was not present throughout all the world's oceans.
The team used chemical techniques to analyse rocks unearthed in Oman that were formed in an ancient ocean around the time of the extinction. Data from six sampling sites, spanning shallow regions to the deeper ocean, revealed that while the water was lacking in oxygen, toxic sulphide was not present. Instead, the waters were rich in iron, suggesting it was this and low oxygen in the waters behind the delay.
The study further showed how oxygen levels varied at different depths in the ocean. While low oxygen levels were present at some depths and restricted the recovery of marine life, shallower waters contained oxygen for short periods, briefly supporting diverse forms of life.
While the precise cause of the long recovery period remains unclear, increased run-off from erosion of rocks on land, caused by high global temperatures, likely triggered anoxic conditions in the oceans.
Said 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."
Apocalypse then
• A mass extinction event around 252 million years ago.
• Followed by a recovery period that lasted five million years.
• Wiped out 96 per cent of all marine species and 70 per cent of terrestrial vertebrate species.
• Some 57 per cent of all families and 83 per cent of all genera became extinct.