Chapter 25 History of life on Earth Macroevolution broad pattern of evolution above the species level Conditions on early earth made the origin of life possible 1 Abiotic synthesis of small organic molecules amino acids nitrogenous bases 4 6 billion years ago earth and solar system formed from dense cloud of dust around the sun Planet constantly bombarded by collisions no water Bombardment Ended 4 2 3 9 billion years ago Atmosphere thick with water vapor and compounds from volcanic eruptions CO2 methane nitrogen hydrogen sulfide and NH3 As earth cooled Hydrogen escaped into space and water condensed Oparin and Haldane earth s early atmosphere was reducing electron giving Organic molecules could have been formed Energy for synthesis from lightning UV radiation primitive soup Urey Miller recreated early soup and made organic molecules Problems o Don t know if early atmosphere was really reducing neutral atmosphere could have also produced organics o Small pockets of reducing environment near volcanoes or deep sea vents Several amino acids could form under conditions like a volcanic eruption Meaning of his experiment o Abiotic synthesis of organic molecules is possible in various ways Meteorites are another possible source Murchison Meteorite had 80 amino acids nitrogenous bases and macromolecules lipids and sugars o Can t be from earth because they are D and L isomers o Organisms on earth make and use only L isomers 2 Joining of small molecules into macromolecules proteins and nucleic acids Abiotic synthesis of RNA can occur spontaneously Dripping solutions of RNA nucleotides amino acids on hot clay sand rocks can produce polymers Complex mix of linked cross linked amino acids but could still have been weak catalysts 3 Packaging of molecules into protocells droplets with membranes that maintained an internal chemistry different from that of surroundings Self replicating molecules metabolism Vesicles fluid filled compartments bounded by a membrane like structure Can exhibit certain properties of life simple reproduction and metabolism and maintenance of internal chemical environment Form spontaneously when lipids organic molecules are added to water o Make a similar lipid bilayer Clay speeded vesicle assembly 4 Origin of self replicating molecules that eventually made inheritance possible 1st genetic material likely RNA Ribozymes RNA that carries out enzyme like catalytic functions Some can make copies of RNA Shown in the lab to eventually be capable of self replication Natural selection the RNA that is easiest to copy with fewest errors will leave the most descendants o Random occurrences Even the simplest protocells could evolve as long as they could replicate RNA could ve provided a template for DNA DNA replicates more accurately useful as genomes got larger Fossil Record documents the History of Life The fossil record o Many changes in organisms over time Organisms went extent Organisms alive today are very different from past organisms Documents new organisms coming from older organisms o Fossil record isn t complete Many organisms not fossilized Many fossils destroyed Not many fossils discovered found Biased towards species that were around for a long time and had morphology conducive to fossilization o High predictive power Tiktaalik discovered because they knew where to look Dating of fossils after o Relative dating dating a fossil relative to the strata around it before or o Absolute dating relies on radioactive decay Half life how decay rate is expressed number of years it takes for 1 of the original sample to react C 14 is the most common Can use U 238 to date really old fossils between layers of volcanic rocks Fossils can provide an understanding of how new features arise and how long it Origin of New Groups of Organisms takes for changes to occur Mammals o Tetrapods have 4 limbs o Mammals fossilize easily and have unique features 1 jaw bone that hinges differently 3 ear bones Canine incisor and molar premolars o Jaws evolved over time in a series of steps Intermediate fossils and so do those that have no living descendants today Chapter 54 Aposematic coloration warning coloration predators avoid prey with a certain coloration Batesian mimicry harmless species mimic a harmful one o Could even include behavior Mullerian Mimicry 2 unpalatable species resemble each other
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