EARTH HISTORY - the universe? A popular hypothesis for the...

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EARTH HISTORY (NOTE: this material covered in lecture on Origin of Much of evolutionary biology involves the history of organic diversity. Organic diversity has been shaped and affected by the origin and history of planet earth. To appreciate this history we need to acquire some knowledge of the geological processes that have shaped the earth. One general theme to consider in this and the next lecture is: if we were to start the history of earth over again from the "primeval soup" would the results be the same? Almost certainly not (see Gould, 1989. Wonderful Life for a detailed discussion). History is unique and events are contingent on what has occurred previously. Much of the contingency of organic evolution is dependent on the unique series of events that shaped the earth, this is why we need to understand some basic geology. How was the planet formed? What is its relationship to other matter in
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Unformatted text preview: the universe? A popular hypothesis for the formation of the earth is the nebular hypothesis . This idea dates back to the philosopher Immanuel Kant (1755) and Laplace (1796) and has been modified as empirical evidence and theory mount. Recent incarnations (chemical -condensation-sequence model) start with the solar system forming from a rotating, diffuse cloud of dust and gasses (a nebula). As the nebula cooled the matter condensed into "planetesimals", near the sun where temperatures were highest elements with the highest melting points (metals and heavy minerals) condensed first. Lower melting temperature elements and compounds (water, methane, ammonia) condensed more readily in the cooler areas further from the sun. This helps to explain the density gradient in the solar system, the closest planets to the sun are terrestrial while those further away are gaseous....
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