A COMET may have sent temperatures soaring 55 million years ago.
Two geologists claim they have evidence that carbon dioxide levels in Earth's atmosphere more than doubled in a single year at the end of the Palaeocene. The increase helped trigger the most extreme change in surface temperatures since dinosaurs ruled the land. The speed of the change makes an extraterrestrial impact the likely cause, they say.
Global temperatures rose by about 5 °C at the end of the Palaeocene – an event known as the Palaeocene-Eocene Thermal Maximum (PETM). Because more CO2 in the atmosphere makes the oceans more acidic, the event can be tracked by looking at the amount of calcium carbonate deposited on the ocean floor by marine organisms. In more acidic waters, less is deposited. Sediment analysis has suggested the increase in CO2 that caused the PETM took between 750 and 30,000 years.
But James Wright and Morgan Schaller at Rutgers University in Piscataway, New Jersey, think it happened much more rapidly. They analysed sediments from a shallow Atlantic Ocean shelf where sediment accumulates faster than it does in the deep sea, making it easier to see seasonal fluctuations in the amount deposited. The pair say that within just one annual cycle about 55 million years ago, the amount of calcium carbonate laid down dropped by 5 per cent. This suggests a very sudden addition – within a year – of atmospheric CO2 (PNAS, doi.org/n8t).
So what could have caused so rapid a release of such a vast amount of CO2? "A large comet impact meets the criteria," says Wright.
If the change to the carbon cycle really was instantaneous, a comet is a good candidate, agrees Dallas Abbott at Columbia University in Palisades, New York – although it would have to have been large to have such a dramatic effect.
This article appeared in print under the headline "Instant climate change! Just add large comet"
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