Tardigrades Survived Five Mass Extinctions

The key to the microscopic tardigrade's astonishing survival record is a unique state of suspended animation known as cryptobiosis. When faced with lethal environmental stress, such as extreme temperatures or a complete lack of water, the water (Review) bear can curl into a desiccated ball called a tun. In this state, its metabolism slows to less than 0.01% of its normal rate. It retracts its legs, sheds nearly all the water from its body, and produces special proteins and sugars that protect its cells from damage, effectively pausing its life until conditions become habitable again.

This remarkable adaptation has made tardigrades the ultimate survivors. Their lineage stretches back over 500 million years, placing them on Earth long before the first major extinction (Review) event. While asteroid impacts, catastrophic volcanic activity, and drastic climate shifts repeatedly reshaped the planet and wiped out dominant species—from ancient marine life to the mighty dinosaurs—tardigrades simply entered their tun state. They could weather the fallout for years, or even decades, before reanimating once the environment stabilized, making them silent witnesses to nearly all of Earth's complex history.