In response to this, I will offer the suggestion that the life forms that live in the extreme climates lived in less extreme climates first. It is possible that some creatures started in "hard mode", but most likely, they progressively adapted to the extreme environments from more palatable climates.
Hard is relative. For example, the filling of the atmosphere with a powerful oxidizer was a major extinction event (the "Oxygen Catastrophe"), yet we do not find it extreme because we are adapted to it.
Even environments that are energy-poor, or cold enough as to inhibit chemical reactions, may support rich forms of life that operate on larger time scales.
