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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. ===================================== 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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