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11-15_16Origin Life_Lecture 31&32

11-15_16Origin Life_Lecture 31&32 - The origin and...

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How many times did life originate? When did life first appear on Earth? How did life first arise on Earth? What were early life forms like? How did early life change Earth’s atmosphere? How did eukaryotic cells originate ? The origin and early evolution of life on planet Earth
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Question #1: How many times? Before the scientific revolution & Darwin: future past
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Charles Darwin’s great insights 1. Organisms share traits, showing evidence of common ancestry (e.g. p53) All life on Earth is related. A Tree of Life 2. New traits arise by descent with modification
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Statistical testing of alternative models strongly supports single ancestry (Theobald 2010) How many times did life originate? The available evidence says “once.”
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When did life originate on Earth? Evidence from chemical & cell-like fossils retained in ancient rocks dated using radioisotopic decay methods.
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1 Ka (kiloannum) = 1 thousand years ago 1 Ma (megannum) = 1 million years ago = 1000 Ka 1 Ga (gigannum) = 1 billion years ago = 1000 Ma Thinking about life’s origins requires large numbers 4 Eons
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Origin of Universe (Big Bang Theory) 13.7 Ga Hadean Eon 4.5 Ga Earth forms, bombarded with space debris from formation of solar system
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Archaean Eon 3.5 Ga Oldest evidence prokaryotic life; Life arose 4.0-3.5 Ga
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The Great Oxidation Event : Earth gets an oxygen- rich atmosphere thanks to photosynthetic cyanobacteria
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Cyanobacteria were very successful.
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