Life as we know it exists on the surface of earth. Life as we are learning more and more about exists in the oceans, even when they are really deep and incompatible with surface life. But there's a whole other biosphere underground, and that means way underground, going down miles under our feet. Down there where it is too hot, dark, and oxygen-depleted for most living things, there are microbes and multicellular life forms that thrive on heat and toxic chemicals. They make their own ecosystems out of whatever they can, including rocks, each other, and even their own bodies. Kurzgesagt shows us some of the bizarre adaptations that living creatures have developed in order to live and even thrive deep in the rocks underground. You might be surprised at the British pronunciation of "methane," which took me off guard. The last two minutes of this video are promotional.