In a ground-breaking study, researchers have found it may have taken only 60,000 years to kill over 90 percent of all life on earth.
This is the most precise study yet of the Permian mass extinction - the greatest die-off in the past 540 million years.
The new timescale is based on more precise dating techniques.
It indicates that the most severe extinction in history may have happened more than 10 times faster than scientists had previously thought.
"We have got the extinction nailed in absolute time and duration," said Sam Bowring, the Robert R. Shrock professor of earth and planetary sciences at Massachusetts Institute of Technology (MIT).
How do you kill 96 percent of everything that lived in the oceans in tens of thousands of years?
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"It could be that an exceptional extinction requires an exceptional explanation," he added.
In addition to establishing the extinction's duration, Bowring and team also found that 10,000 years before the die-off, the oceans experienced a pulse of light carbon - which likely reflects a massive addition of carbon dioxide to the atmosphere.
This dramatic change may have led to widespread ocean acidification and increased sea temperatures by 10 degrees Celsius or more, killing the majority of sea life, said the study.
But what originally triggered the spike in carbon dioxide?
"It is clear that whatever triggered extinction must have acted very quickly," added Seth Burgess, lead study author and a geochemist at MIT.
"It was fast enough to destabilise the biosphere before the majority of plant and animal life had time to adapt in an effort to survive," he added.
The researchers visited Meishan in China - a region whose rock formations bear evidence of the end-Permian extinction.
They sampled rocks from this area as well as from nearby alternating layers of volcanic ash beds and fossil-bearing rocks.
The researchers determined a much more precise 'age model' for the end-Permian extinction, which now appears to have lasted about 60,000 years - with an uncertainty of 48,000 years - and was immediately preceded by a sharp increase in carbon dioxide in the oceans.
The Permian mass extinction marks the end of the Permian geologic period, which ended approximately 252 million years ago.
More than 96 percent of marine life and 70 percent of land species perished.
By comparison, 85 percent of life died off during the dinosaur-killing extinction at the end of the Cretaceous period, 66 million years ago.
"We have refined our approach and now we have higher accuracy and precision. You can think of it as slowly spiraling in toward the truth," said Bowring in the study published in the journal National Academy of Sciences.