He estimates f_l, the probability of life arising in a habitable planet, as 0.1.<p>Abiogenesis has never been observed to occur independently of its presumed occurrence when life started on Earth.<p>Given the current state of scientific knowledge on this topic, the only certain lower bound on this number is the probability of molecules in a suitable &quot;organic soup&quot; arranging themselves into a self-contained bacterium. And that probability is a _very_ small number.<p>If f_l is _very_ small, then there is no need to be pessimistic about our own long-term survival. We see no advanced alien civilisations, because there is no other life out there of any kind - the rest of the observable universe is sterile.