Archaea are microbes. Most live in extreme environments. These are called extremophyles. Other Archaea species are not extremophiles and live in ordinary temperatures and salinities. Some even live in your guts!

Some extremophile species love the heat! They like to live in boiling water, like the geysers of Yellowstone Park, and inside volcanoes. They like the heat so much that it has earned the nickname "thermophile", which means "loving heat", and it would probably freeze to death at ordinary room temperature. Other extremophile Archaea love to live in very salty, called hypersaline, environments. They are able to survive in these extreme places where other organisms cannot. These salt-loving Archaea are called halophyles.

Archaea was originally thought to be just like bacteria, but archaea is a much different and simpler form of life. It may also be the oldest form of life on Earth!

Archaea requires neither sunlight for photosynthesis as do plants, nor oxygen. Archaea absorbs CO₂, N₂, or H₂S and gives off methane gas as a waste product the same way humans breathe in oxygen and breathe out carbon dioxide.

Planets which contain an environment wherein archaea might survive include Venus, the past environment of Mars, Jupiter, Saturn, and Jupiter's moon Io.