Thermophiles, a type of extremophile, produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park

An extremophile is an organism (a living thing) which lives best in extreme conditions that are harmful to most life on Earth. They are different from organisms that live in normal places, called mesophiles or neutrophiles.

In the 1980s and 1990s, biologists found that microbes can survive in extreme environments. These are niches that are extreme in some way. They may be extremely hot, or cold, or dry, or under huge pressure, or very salty or acidic. Complex organisms, such as animals or plants, cannot live in these environments.