The Evolutionary Biology Lecture of the Week for July 10, 2006 is now available
at:

http://aics-research.com/lotw/

The talks center primarily around evolutionary biology, in all of its aspects:
cosmology, astronomy, planetology, geology, astrobiology, ecology, ethology,
biogeography, phylogenetics and evolutionary biology itself, and are presented
at a professional level, that of one scientist talking to another. All of the
talks were recorded live at conferences.

This is the eighth lecture in a summer-long series on the new science of
astrobiology.

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July 10, 2006

Part VIII: Astrobiology

Evolution of the Early Atmospheres of Venus, Earth and Mars

David Catling, University of Bristol

23 min.

"Fire, air, water, earth, we assert, originate from one another, and each of
them exists potentially in each, as all things do that can be resolved into a
common and ultimate substrate".

— Aristotle, 384 BC – 322 BC

In the current movie, "An Inconvenient Truth," Al Gore quotes Carl Sagan,
saying that the Earth's atmosphere is approximately as thick proportionally as
the layer of varnish is on a large globe. In reality, it's thicker than that,
but not by much.

If water is the sine qua non of life, then an atmosphere of a minimum surface
pressure is the sine qua non of water. Without sufficient pressure and heat,
liquid water can't exist on a planet's surface.

Planetary conditions foster life, and in turn, life changes the evolution of
the planet. Oxygen atmospheres overlaying oceans of water is not an equilibrial
condition and they should not be expected a priori in any simple chemical
thermodynamical model.

Whether life exists on other planets remains one of the great unanswered
questions. Recent research argues that an atmosphere rich in oxygen is the most
feasible source of energy for complex life to exist anywhere in the universe,
thereby limiting the number of places life may exist.

In this lecture, Catling outlines the evolution of the atmospheres of Venus,
Earth and Mars. Two factors, as you will see, significantly predetermine the
evolution of those atmospheres: planetary position and size.