Book I'm reading talks about the deep biosphere, life existing kilometers beneath the bottom of the ocean on Earth. Reassuring, really. Even if we manage to kill every living thing on the surface and in the oceans, there is a reservoir of biological life that will recolonize & re-establish biodiversity on Earth in a few hundred million years - an eyeblink. Maybe even develop intelligence. This can happen perhaps twice more before the sun renders the planet uninhabitable. https://en.wikipedia.org/wiki/Deep_biosphere