Extremophiles are in no sense rare. They constitute the most diverse collection of branches of the tree of life. We are on one of those.
This is not accidental. There is more genetic variation in humans in Africa than the whole rest of the world, and more variation in English dialects in England than the whole rest of the world. We -- everything we knew existed until recently -- evolved from extremophiles. They came first. The world changed around them. Some changed to match, eventually giving rise to us, while others found places more like what they were used to. The latter are still to be found in those places, and in many others they have also adapted to.
Common types like us are adapted to currently common conditions. When the environment changes radically, and all the life we knew of up until recently is extinct, the extremophiles will radiate a new ecosystem adapted to new conditions.
This is not accidental. There is more genetic variation in humans in Africa than the whole rest of the world, and more variation in English dialects in England than the whole rest of the world. We -- everything we knew existed until recently -- evolved from extremophiles. They came first. The world changed around them. Some changed to match, eventually giving rise to us, while others found places more like what they were used to. The latter are still to be found in those places, and in many others they have also adapted to.
Common types like us are adapted to currently common conditions. When the environment changes radically, and all the life we knew of up until recently is extinct, the extremophiles will radiate a new ecosystem adapted to new conditions.