Life on Earth is incredibly abundant — and adaptable. From the freezing, dry valleys of Antarctica, to hot springs with conditions akin to boiling battery acid; from smoking hydrothermal vents deep below the ocean surface, to the high-altitude ice sheets of the Himalayas; there are few places on Earth that life has not colonized. From the single-celled ancestor that first arose on Earth 3.6 billion years ago, evolution has wrought an incredible variety of forms, including at least one species, Homo sapiens, with the capacity to ponder its own origins. Does other life exist in the Universe, and what does it need to survive?