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Origin and History of Life Chapter 19 Mader: Biology 8th Ed. Outline • • • • • • • • • Primitive Earth Origin of First Cells Fossils The Precambrian The Paleozoic The Mesozoic The Cenozoic Continental Drift Mass Extinctions Mader: Biology 8th Ed. The Primitive Earth • Primitive atmosphere most likely consisted of water vapor, nitrogen, and carbon dioxide, with small amounts of hydrogen and carbon monoxide. – Little free oxygen. – Originally too hot for anything but water vapor to form. – Earth cooled and water vapor condensed to liquid water. Mader: Biology 8th Ed. Monomers Evolve • Stanley Miller (1953) conducted an experiment to show the first organic molecules could have been produced from primitive atmospheric gases in the presence of strong energy sources. Mader: Biology 8th Ed. Polymers Evolve • Monomers join to form polymers in the presence of enzymes. – Protein-First Hypothesis assumes DNA genes came after protein enzymes arose. – RNA-First Hypothesis suggests only RNA was needed to progress toward formation of the first cell or cells. Mader: Biology 8th Ed. Protocell Evolves • Protocells would have been precursors to the first true cells. – A protocell is a structure with a lipidprotein membrane that carries on energy metabolism. Semipermeable-type boundary may form around coacervate droplets. Liposomes form in liquid environments. Mader: Biology 8th Ed. Protocell Anatomy Mader: Biology 8th Ed. Origin of First Cells Mader: Biology 8th Ed. Fossils • Fossils are remains and traces of past life. – Great majority are found embedded in, or recently eroded from, sedimentary rock. Sediment becomes a stratum. Recognizable layer in stratigraphic sequence. Paleontology is the study of the fossil record. Mader: Biology 8th Ed. Fossils Mader: Biology 8th Ed. Relative Dating of Fossils • Strata change their character over great distances. – A stratum of the same age tends to contain the same fossil. Helps geologists determine relative dates of the strata despite upheavals. Mader: Biology 8th Ed. Strata Mader: Biology 8th Ed. Absolute Dating of Fossils • One absolute dating method relies on radioactive dating techniques. – All radioactive isotopes have a particular half-life. Length of time it takes for half of the radioactive isotope to change into another stable element. Compare radioactivity of a fossil to that of a modern sample of organic matter. Mader: Biology 8th Ed. The Precambrian • Comprises about 87% of the geological timescale. – First cells came into existence. Prokaryotes Cyanobacteria in ancient stromatolites added oxygen to the atmosphere. Lack of ozone shield allowed UV radiation to bombard Earth. Mader: Biology 8th Ed. Prokaryote Fossil of Precambrian Mader: Biology 8th Ed. The Precambrian • • Eukaryotic Cells Arise – Eukaryotic cell arose about 2 bya. Nearly always aerobic and contains nucleus as well as other membranous organelles. Endosymbiotic Hypothesis. Multicellularity Arises – Multicellularity arose approximately 1 billion years later (1.4 bya). Mader: Biology 8th Ed. The Paleozoic • The Paleozoic era lasted over 300 million years. – Contained three major mass extinctions. Disappearance of a large number of species, or a higher taxonomic group, within a relatively small time interval. Mader: Biology 8th Ed. Cambrian Animals • Molecular Clock is based on principle that DNA differences in certain parts of the genome occur at fixed rate, and are not tied to natural selection. – Number of base-pair differences tells how long two species have been evolving separately. High Cambrian diversity may be due to the evolution of outer skeletons. Mader: Biology 8th Ed. Cambrian Sea Life Mader: Biology 8th Ed. Invasion of Land • • • Plants – Seedless vascular plants date back to Silurian period and later flourished in Carboniferous period. Invertebrates – Outer skeleton and jointed appendages of arthropods are adaptive to living on land. Vertebrates – Evolution of fishes began in Ordovician. Mader: Biology 8th Ed. The Mesozoic Era • Evolution of many plants and animals continued into the Triassic, the first period of the Mesozoic era. – Nonflowering seed plants became dominant. – Dinosaurs achieved enormous size. – Mammals remained small and insignificant. Mader: Biology 8th Ed. The Cenozoic Era • Mammals began an adaptive radiation at the end of the Mesozoic era, moving into habitats left vacant by the demise of dinosaurs. – Flowering plants already diverse and plentiful. – Primate evolution began. Mader: Biology 8th Ed. Factors That Influence Evolution • Continental Drift – Positions of continents and oceans are not fixed. Modern mammalian biological diversity is the result of isolated evolution on separate continents. Mader: Biology 8th Ed. Continental Drift Mader: Biology 8th Ed. Continental Drift • Plate Tectonics – Movements of Earth’s crust which is fragmented into slablike plates that float on a lower hot mantle layer. Mader: Biology 8th Ed. Plate Tectonics Mader: Biology 8th Ed. Mass Extinctions • At least five mass extinctions have occurred throughout history. At the ends of: – Ordovician Continental Drift – Devonian Bolide Event Loss of 70% of marine invertebrates Mader: Biology 8th Ed. Mass Extinctions – – – Permian Excess carbon dioxide. Loss of 90% of ocean species. Triassic Meteorite Collision Cretaceous Mader: Biology 8th Ed. Review • • • • • • • • • Primitive Earth Origin of First Cells Fossils The Precambrian The Paleozoic The Mesozoic The Cenozoic Continental Drift Mass Extinctions Mader: Biology 8th Ed. Mader: Biology 8th Ed.