Yellowstone is defined, in large part, by its huge number of hydrothermal features. There are about 10,000 examples throughout the park, including geysers, fumaroles, mudpots and hot springs. These all look amazing, of course, but there’s more to them than that, as they’re full of microorganisms that thrive in extreme heat. Photo credit: Daniel Mayer/Wikimedia Commons | CC BY-SA 3.0