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Chapter 24

Chapter 24 Summary Cosmic Perspective

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Western University
Astronomy 1021
Chris Racknor

CHAPTER TWENTY FOUR Life in the UniverseWhen Life Arose on EarthFossil evidence puts the origin of life at least 35 billion years ago and carbon isotope evidence puts this date to more than 385 billion years ago life therefore arose within a few hundred million years after Earths birth and possibly in a much shorter time How Life Arose on Earth Genetic evidence suggests that all life on earth evolved from a common ancestor that was probably similar to microbes living today in hot water near undersea volcanic vents or hot springs we do not know how this first organism arose but lab experiments suggest that it may have been the result of natural chemical processes on early earth once life arose it rapidly diversified and evolved through natural selection The Necessities of Life Life on earth survives in a wide range of environments and in general seems to require three things which are a source of nutrients a source of energy and liquid water The Possibility of Life on Mars Mars once had conditions that may have been conducive to an origin of life if life arose it might still survive in pockets of liquid water underground The Possibility of Life on Europa or Other Jovian Moons Europa probably has a subsurface ocean of liquid water and may have volcanoes on its ocean floor if so it has conditions much like those in which life on earth probably arose making it a good candidate for life Ganymede and Callisto might have oceans as well Titan may have other liquids on its surface though it is too cold for liquid water perhaps life can survive in these other liquids or perhaps Titan has liquid water deep underground Enceladus also shows evidence of subsurface liquids offering yet another possibility for life Where We Might Find Habitable Planets Billions of stars have at least moderate size habitable zones in which life bearing planets might exist with the Kepler mission scientists hope soon to find evidence of potentially habitable worlds The Commonality of Earthlike Planets We do not know how common or rare earthli
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