Five million years before India collided with Asia, the Earth experienced a sharp warming. It is known as the PETM (Palaeocene-Eocene Thermal Maximum). Over a time span of no more than four thousand years, the Earth’s surface temperature jumped up by about 5 °C. This abrupt hot spell lasted for about 20 thousand years, after which the temperature slowly returned to its pre- PETM level.

This event was discovered by Jim Kennett and Lowell Stott in 1991. At a depth of 170 metres in a sediment core from the Southern Ocean, they encountered puzzling anomalies in the δ18O...

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