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TAMU BIOL 112 - Chapter 25 History of life on Earth

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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 possible1. 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 organicso 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 experimento 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 isomerso Organisms on earth make and use only L isomers2. 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 catalysts3. 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 watero Make a similar lipid bilayer- Clay speeded vesicle assembly4. 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 descendantso 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 largerFossil Record documents the History of Life- The fossil recordo Many changes in organisms over time Organisms went extent Organisms alive today are very different from past organisms Documents new organisms coming from older organismso 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 fossilizationo High predictive power Tiktaalik discovered because they knew where to look- Dating of fossilso Relative dating- dating a fossil relative to the strata around it “before” or ”after”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 rocksOrigin of New Groups of Organisms- Fossils can provide an understanding of how new features arise and how long it takes for changes to occur- Mammalso Tetrapods- have 4 limbso Mammals fossilize easily and have unique features 1 jaw bone that hinges differently 3 ear bones Canine, incisor and molar/premolarso Jaws evolved over time in a series of steps Intermediate fossils and so do those that have no living descendants todayChapter 54- Aposematic coloration-warning coloration predators avoid prey with a certain coloration- Batesian mimicry- harmless species mimic a harmful oneo Could even include behavior- Mullerian Mimicry- 2+ unpalatable species resemble each


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