Paleocene–Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (or PETM) was a time about 56 million years ago when the Earth got much, much hotter. It happened really quickly - in less than 10,000 years - which is very fast in geologic time. During the PETM, the Earth's average temperature increased by 8-9° Celsius (14-16°F) and the sea level went up a lot. As the Earth got warmer, many animals and plants died. Scientists aren't sure why it happened so quickly, but they think it was probably because the Earth's oceans released a lot of carbon dioxide all at once, causing the temperature to go up.