Lecture of the Week: Part VIII: Astrobiology

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.

David Catling at Bristol University, along with colleagues at the
University of Washington and NASA, have recently contended that
significant oxygen in the air and oceans is essential for the evolution
of multicellular organisms, and that on Earth the time required for
oxygen levels to reach a point where animals could evolve was almost
four billion years.

Because four billion years is almost half the anticipated life-time of
our sun, life on other planets orbiting short-lived suns may not have
had sufficient time to evolve into complex forms. This is because
levels of oxygen will not have had time to develop sufficiently to
support complex life, before the sun dies. This may well be a major
limiting factor for the evolution of life on otherwise potentially
habitable planets.

Catling comments: "Earth's surface is stunningly different from that of
its apparently lifeless neighbours, Venus and Mars. But when our planet
first formed its surface must also have been devoid of life. How the
complex world around us developed from lifeless beginnings is a great
challenge that involves many scientific disciplines such as geology,
atmospheric science, and biology".

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.

Because this talk was originally presented at a conference on early
Mars, Catling ends the lecture emphasizing the nature of the evolution
of the current Martian atmosphere.

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