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BIOL 1202 - 1 - H istory of Life on Ea rth Spontaneous...

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History of Life on Earth Spontaneous Generation What people believed a few centuries ago People thought that new living things appeared all of the time Refutation Louis Pasteur (mid-1800’s) Performed a simple experiment to refute spontaneous generation Boiled broth in a flask to kill existing microorganisms As broth cooled, condensing water collected in a tube, sealing the flask Nothing grew in the flask To further prove his point, he broke the sealing tube off and placed the now open flask outside, exposed to microorganisms Mold grew in the flask Conditions on Early Earth Atmosphere Contained CO 2 , CH 4 , NH 3 , H 2 , N 2 , HCl, H 2 S, H 2 O No free oxygen Frequent lightning storms Frequent volcanic eruptions Frequent meteor impacts UV light from sun
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No ozone layer Earth Before Life Arose Earth is about 4.6 billion years old Radiometric dating of meteorites & moon rocks Life arose about 3.8 billion years ago Chemical traces in rocks 3.8 BYA Fossilized bacteria in rocks 3.5 BYA No further spontaneous generation Radiometric Dating 40 K naturally decays to 40 Ar Used to measure to rate of decay in inorganic rocks Experiment of Miller & Urey Attempted to reproduce the origin of life by replicating the conditions of early earth After only a few days, formed organic molecules necessary for life Failed to form life How to Assemble a Living Thing Several things required Accumulation of organic molecules Catalyze reactions Reproduce from stored genetic info Separate the living thing from the outside environment
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Chicken or Egg complex DNA required to make proteins Proteins required to make DNA Which came first? Ribozymes RNA molecule that can catalyze reactions, especially those involved in synthesis and processing of RNA itself How earliest cells formed Earliest cells used RNA to store info Ribozymes to catalyze reactions Summary Water + elements + energy Prebiotic soup of amino acids, nucleotides, lipids, and sugars formed Microsphere-like protocels surrounding more complex organic molecules like RNA, carbohydrates, proteins, and lipids First prokaryotes First organisms were anaerobic prokaryotes Bacteria & Archaea Would have started to compete for energetic organic molecules Photosynthetic bacteria evolved 3.5 BYA CO 2 + H 2 O Food + O 2 O 2 accumulates in atmosphere 2.2 BYA Aerobic metabolism evolves
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First Eukaryotes appear 2–1.7 BYA Origin of Modern Organisms First living organisms were likely anaerobic prokaryotes Found in stromatolites All living things come from these first prokaryotes Evolution by natural selection shows how this occurred Models Static Model All species originate at the same time Stay in their exact form Transformation Model All species originate at the same time Change over time, but do not speciate Separate Types A few species originated originally Evolved over time Branched off into many different species Common Descent One species originated originally Anaerobic prokaryote Evolved over time
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Branched off into many different species Endosymbiont Hypothesis
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