If our body temperature falls below 30 degrees C or so, it stops functioning properly and we die. 30 C seems still a rather warm temperature for normal chemical reactions to be able to occur, and in most environmental conditions inhabited by men it still represents a temperature gradient compared to the cooler external environment. Which metabolic processes or chemical reactions fail at such temperatures? Why do we need such a high body temperature to function properly? And a related question: By now life has evolved a wide spectrum of solutions to cope with a relatively wide range of external temperatures, from Tardigrades or frogs who can survive in freezing temperatures (or warm blooded animals of course) to thermophile bacteria who can survive over-boiling temperatures, but for simpler very early life to develop, which is the range of temperatures believed to be needed?