HYDROTHERMAL VENTS are the planet’s exhaust pipes. Kilometres beneath the ocean surface, they relentlessly belch out searing hot water rife with harsh chemicals from beneath Earth’s crust. When they were first discovered in 1977, nobody expected these inhospitable sites to bear signs of life. And yet, thriving alongside these vents were colonies of tubeworms, mussels and clams entirely new to science. It is hard to think of an environment that could be more hostile. Now new work is revealing evidence that these animals are raising their young in just such a place: the fractured rocks beneath the vents themselves.