The warmest period in the Cenozoic era was caused by a massive release of carbon into the atmosphere, likely triggered by widespread volcanic activity.
# Metadata
Title: Paleocene–Eocene Thermal Maximum Movietime: 11:12 Geographical Time: 50 Ma
Around 56 to 50 million years ago, Earth experienced a dramatic and abrupt global warming event known as the Paleocene–Eocene Thermal Maximum (PETM). Temperatures rose by 5–8°C over a relatively short geologic timespan — a few thousand years — and remained elevated for tens of thousands more.
The cause was likely extensive volcanic activity associated with the opening of the North Atlantic Ocean. This volcanism released vast quantities of carbon dioxide and methane into the atmosphere, creating a greenhouse effect.
The PETM profoundly altered global climate patterns, ocean chemistry (including acidification), and ecosystems. It caused a major extinction in deep-sea life and drove the rapid evolution and dispersal of mammals and other land animals, setting the stage for modern biodiversity.