ch4 - Today's topic - "R a r e E a r t h H y p o t h e...

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Today's topic - " Rare Earth Hypothesis " Based on a book "Rare Earth by Peter Ward & Donald Brownlee (2000) PCL Library. University of Washington. ===================================================== They think that bacterial life is likely to be common in the universe. For the usual reasons: It evolved quickly on earth. Extremophiles can thrive in a very wide range of conditions: Deep subsurface rocks, deep ocean, wide temperature range. ====================================================== Then they consider the conditions required for complex animal life to evolve. They argue that the history of life on earth suggests that the requirements are so strict, that it is unlikely that complex animal life would evolve except under the rarest circumstances. ======================================================= What are the requirements for complex life? 1) Planet is the right distance from star . 2) Right mass of star . 3) Stable planetary orbits (no large planet in a high-eccentricity orbit). 4) (big enough to retain atmosphere, solid/molten metallic core for magnetic field) 5) A Jupiter in the solar system (creates a region of low density of comets and asteriods)
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6) Water, but not too much, not too little . I had not thought much about this before - on earth we seem to have just the right amount of water - How likely is that? 7) The
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ch4 - Today's topic - "R a r e E a r t h H y p o t h e...

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