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Chapter 3

Chapter 3.doc

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BIOL 2400
Cortland Griswold

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Evolution - Chapter 3 3.1 The Ancient Earth • Darwin rejected the theory that the Earth was only a few 1000 yrs old. Believed it was billions. • Darwin formerly a geologist • through the study of rock formation Darwin concluded the Earth had to be billions of years old • Darwin’s critic Kelvin, argued that the Earth wasn’t as old as they thought. His argument was based on the temperature of rocks: • the earth began as a ball of molten rock, it cooled and hardened; the heat from the core escaped into space. Rocks cool at a steady rate so you can calculate the age of rocks underground and therefor the age of the planet. He was wrong. • planet’s interior is dynamic • 1900’s: physicists discover the absolute way to age rocks • radioactive isotopes decay into other elements at a precise rate • allow narrow estimate for fossils • tests show Earth is 4.568 billion years old 3.2 A Vast Museum • fossil record is far from complete • organisms only rarely become fossils • over thousands of years, the sediment surrounding the organism turns to rock, fossil exposed later by erosion or other means • it is rare for soft tissues to mineralize • Lagerstätte(n): a site w/ an abundant supply of unusually well-preserved fossils from the same period of time. • soft tissue fossils are extremely important to scientists b/c they preserve such an incredible amount of detail. Mainly formed in anoxic, lifeless pools, lagoons or bays • Burgess Shale: A Lagerstätten in Canada that preserved fossils from the Cambrian period • quarries from this burgess shale have yield more than 65, 000 specimens (mostly soft-body) representing 93 species fossils have revealed many things to scientists about the lives of prehistoric • animals • the shape of an animals ear bones determines which frequencies it is most sensitive to • biomarker: molecular evidence of life in the fossil record. Biomarkers can include fragments of DNA , molecules such as lipids or isotopic ratios • the molecules in fossils and rocks can tell scientists many things about its origin • technology allows scientists to gain new sights into the behavior and appearance of extinct species from their fossils • isotopes and biomarker molecules carry info about the history of life 3.3 Life’s Earliest Marks •stromatolites: layered structures formed by the mineralization of bacteria. Grow on the floors of lakes and shallow seas. Modern ones only occur in extreme environments •potential signs of life date back as far as 3.7 billion years ago •the oldest known fossils that are generally accepted are 3.45 billion yrs old •the earliest signs of life are microbial, and microbes still constitute most of the world’s biomass and genetic diversity 3.4 The Rise of Life • life dominated by 3 major domains: Bacteria: one of the 2 prokaryote domains of life. Bacteria includes - organisms such E.Coli, and other familiar microbes -Archaea: One of the 2 prokaryote domains of life. Archaea resemble bacteria, but they are distinguished by a number of unique biochemical features -Eukarya: A domain of life characterized by unique traits, including membrane-enclosed cell nuclei and mitochondria. Includes animals, plants, fungi, and protists single celled eukaryotes) •the earliest signs of life resemble living bacteria •first signs of cyanobacteria emerged at the same time the first evidence of atmospheric oxygen appeared. Rise in oxygen due to emergence of cyanobacteria • archaea have an early and ambiguous first appearance in fossil record around 3.5 billion years ago •only known organism today that produces methane is a lineage of archaea calle
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