Comment on "Does the rapid appearence of life on Earth suggest that life   is common in the Universe"
  In a recent paper [1] Lineweaver and Davis performed a statistical analysis to claim that the rapidity of biogenesis on Earth indicates high probability of biogenesis on terrestrial- type planets. We argue that the rapid appearance of life on Earth hardly tells us anything about the probability of life to appear on other planet. The conclusion should be different. The rapid initial biogenesis is consistent with a large number ($N \sim 10$) of crucial steps in evolution from simplest life forms to humans. 
V.V. Flambaum