And the answer: Extremophile.
Extremophiles thrive in conditions that we humans find extreme, such as environments with no oxygen. The most common example of this microorganism is the "archaea," which has the potential to explain how life began on Earth.
When we refer to an extreme environment, we mean an environment that is seemingly inhospitable to human life. While we need oxygen, food, shelter, and water to survive (to name a few), some select few organisms can survive with a lot, lot less. In fact, just a lack of oxygen isn’t enough to deter the life of some of these curious extremophiles—very high or low temperatures, or extreme pressure can also be examples of environments where extremophiles thrive.
Extremophiles secrete enzymes called "extremozymes," which enable them to function in forbidding environments. Interestingly, these exact enzymes could hold powerful tools for genetically based medications as well as industrial chemicals and processes. Because the enzymes remain active under severe conditions, they are incredibly useful to certain scientific research applications (which require similarly extreme conditions!).
The study of extremophiles also offers a glimpse into ancient life on Earth. Before evolution had a chance to get going, Earth was once an inhospitable rock subject to extreme conditions. In fact, the first single-celled organisms cells were most likely occupying deep ocean and subterranean habitats, as the lack of oxygen in the atmosphere and ozone layer would have forced life to remain on the dim ocean floor. Since many extremophiles today occupy similar environments, this has led to the theory that extremophiles are living examples of ancient organisms, and thus are models of ancient life.
Learn more about extremophiles and the habitats they populate here.