Most animals live in conditions where the temperature is between 4°C and 40°C (39°F-104°F), the pH (which measures acidity and alkalinity) is between 5 and 9, and oxygen is abundant. Some animals, called extremophiles, live in conditions that are outside these ranges. The term "extremophile" is given to micro-organisms that live in extreme environments. These environments range from hot springs to sea ice to brine lakes to deep-ocean hydrothermal (hot water) vents. Each of these environments has conditions that are considered punishing or even unbearable for most animals. However, extremophiles thrive under these conditions. Extremophiles may also provide a glimpse of what the earliest forms of life looked like.

Extremophiles are part of a new kingdom of animals called Archae. The members of this kingdom look like bacteria and were considered a phylum in the Kingdom Monera. In the late-twentieth century, however, scientists separated the Archae from other bacteria...