THE ORIGIN OF LIFE - DID IT OCCUR AT HIGH-TEMPERATURES

A high-temperature origin of life has been proposed, largely for the r eason that the hyperthermophiles are claimed to be the last common anc estor of modern organisms. Even if they are the oldest extant organism s, which is in dispute, their existence can say nothing about the temp eratures of the origin of life, the RNA world, and organisms preceding the hyperthermophiles. There is no geological evidence for the physic al setting of the origin of life because there are no unmetamorphosed rocks from that period. Prebiotic chemistry points to a low-temperatur e origin because most biochemicals decompose rather rapidly at tempera tures of 100 degrees C (e.g., half-lives are 73 min for ribose, 21 day s for cytosine, and 204 days for adenine). Hyperthermophiles may appea r at the base of some phylogenetic trees because they outcompeted the mesophiles when they adapted to lower temperatures, possibly due to en hanced production of heat-shock proteins.