Abstract

It is possible that the Earth is a very odd planet with a rare combination of properties that make it particularly suitable for the emergence of a complex biosphere.  This leads to a potential for severe observational bias since we obviously must inhabit an inhabitable-planet even if such places are extraordinarily peculiar.  This “anthropic selection” effect may severely distort our understanding of the Earth.  For example, the long-term stability of the Earth’s climate (no complete freeze-up or runaway greenhouse in 4 billion years) may not be the result of stabilizing feedback mechanisms, as often assumed, but may instead be the result of chance.  Another example is that the early emergence of life on Earth shortly after the appearance of liquid water does not, necessarily, imply that life appears easily once conditions are suitable; planets where life drags its feet over starting may not be inhabited for long enough to allow the emergence of anything other than very simple organisms.  A final example is that the Gaia hypothesis may have confused cause and effect; perhaps a stable environment is a precondition for the emergence of a complex biosphere rather than its consequence.

Hence, a proper understanding of our planet requires us to answer the question “Is the Earth special?”.  In this talk I will present evidence that a large dose of luck was indeed necessary to give us the four billion years of good weather the Earth has enjoyed.  In particular, Phanerozoic temperature history is incompatible with feedback control and the properties of the Earth-Moon system are fine-tuned to put us in a “sweet-spot” between climate-chaos, on the one hand, and frequent snowball-Earth episodes, on the other.

Further information

All UoB staff and students welcome.  There will be a wine and beer reception after this event in the Earth Sciences Common Room