The History of Life on Earth

The History of Life on Earth - Protobionts-Aggregates of...

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The History of Life on Earth Chapter 25 Early Earth - Earth is about 4.6 billion years (BY) old -Radiometric dating of meteorites & moon rocks - Life arose about 3.8 (BY) ago -Chemical traces in rocks BY -Fossil bacteria in rocks - No spontaneous generation now, but must have happened then Condistions on Early Earth 1. Atmosphere - CO2; CH4;NH3;H2S;H2O - No free oxygen 2. Abundant energy to drive reactions - Frequent storms w/ much lightning - Frequent volcanic eruptions - Frequent meteor impacts - UV light from the sun Testable hypotheses explaining the origin of life 1. Abiotic synthesis of small organic molecules 2. Joining these molecules into polymers 3. Packaging these molecules into “protobionts” 4. The origin of self-replicating molecules Miller & Urey Experiments - Figure 4.2 Alternative Hypotheses 1. First organic compounds may have been synthesized near hydrothermal vents 2. Extraterrestrial origin Abiotic Synthesis of Polymers - Small organic molecules polymerize when they are concentrated on hot sand or clay
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Unformatted text preview: Protobionts-Aggregates of abiotically produced molecules surrounded by a membrane-Liposomes can form when lipids or other organic molecules are added to water The Chicken or the Egg Now-DNA->RNA->Protein-Need proteins to synthesize more DNA Then-Earliest cells used RNA to store info-Ribozymes to catalyze reactions Ribozymes-Found to catalyze many different reactions including-Self splicing-Making complementary copies of short-stretches of RNA Possible sequence leading to first prokaryotes Concept 25.2: The fossil record documents the history of life Fossils Document the History of life-Sedimentary strata reveal the relative ages of fossils -Fossils near surface more recent-Deeper fossils more ancient-Fossil records shows great changes in organisms through time Dating of Fossils-Order of fossils in rock strata tells us the sequence in which they were laid down-This provides relative ages, not absolute dates...
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This note was uploaded on 03/27/2010 for the course BIOL 1202 taught by Professor Gregg during the Spring '08 term at LSU.

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The History of Life on Earth - Protobionts-Aggregates of...

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