Origins_of_Life - Origins of Life Stephen Eikenberry 31...

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Origins of Life Stephen Eikenberry 31 August 2010 AST 2037 1
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How Did Life Come About? First things first: I don’t know! Second: Anyone who says they have a proven scientific explanation (currently) is probably selling something! That said … there ARE some things we know, and some we strongly suspect From them, we can at least TRY to put together a rough sketch of how life probably arose here on Earth Let’s do that! 2
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What do we have to work with? In the beginning … OK, well, not really the beginning. More like: About 8 billion years after the Big Bang About 500 million years after the Solar System began to form About 4.6 billion years before TODAY What was Earth like? Young, recently-solidified surface Accretion of material from planetesimals nearing an end (end of the “Early Heavy Bombardment”) How do we know? 3
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Earth: T – 4.6 Billion Yrs Rocks were just solidifying on surface How do we know? Age-dating of the oldest known rocks From what? Radioactive isotope dating Huh? First: what’s an isotope? 4
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Elements and Isotopes An “element” has a certain number of protons and electrons For instance, hydrogen (H) has 1 of each Oxygen (O) has 8 of each Carbon (C) has 6 of each “Isotopes” of a given element have the same number of protons/electrons, but different numbers of neutrons in the nucleus: “Normal” H has 0 neutrons, deuterium has 1 neutron, tritium has 2 neutrons – but ALL are still hydrogen O 16 is “normal” oxygen, most common – has 8 protons and 8 neutrons (8+8 = 16) O 18 is more rare (8 protons + 10 neutrons = 18) C 12 (6+6) is common, C 14 (6+8) is rare – and radioactive!! 5
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Radioactive Decay Many non- “normal” isotopes are radioactive, and they “decay” into other elements This process converts a “parent” to a “daughter” isotope This happens on a known timescale called the “half-life” of the decay (the time it takes for ½ of the parent atoms to decay) 6
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Radioactive Age-Dating So … by counting parent/ daughter atoms inside a rock, we KNOW how many half-lives since the rock solidified from magma We can measure the atomic half-life in a physics lab (or, even calculate it from quantum physics these days) Then, we know HOW OLD the rock is … 7
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Some Handy Decays 8 Parent Isotope Stable Daughter Product Half-Life Uranium-238 Lead-206 4.5 billion yr Uranium-235 Lead-207 704 million yr Thorium-232 Lead-208 14.0 billion yr Rubidium-87 Strontium-87 48.8 billion yr Potassium-40 Argon-40 1.25 billion yr Samarium-147 Nedodymium-143 106 billion yr
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Earth: T – 4.4 Billion Yrs
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