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Chapter 15.1.docx

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GOPH 375
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Chapter 15  For organisms to be fossilized: must have dense, robust hard parts (teeth, shells, bones) and rapid burial (not scavenged or disintegrated). Fossilization preserves even small features  Amber fossilization – insects caught in tree sap  Footprints are fossils too  As glaciers retreat, frozen animals are found with flesh on their bones and food in their stomach  Curvier proved extinction, and recognized that it happen at one time  Law of superposition: younger layers of sediment are deposited on top of older layers  Hooke proposed the idea of extinction events, and fossils could be used as dating tools  Principle of faunal succession: strata of like age can be recognized by the assemblage of fossils they contain  Once geological timescale was created, dates were added using radioactive elements in igneous rock (paleontology)  Archaea: relatives of the earliest life forms on earth, killed by oxygen  Earliest organisms lived in the water, only came on land when oxygen formed an ozone to protect land from suns UV rays  Cambrian Explosion – organisms started developing hard parts (possibly as protection)  Species level of the hierarchy is where evolution and extinction occur. Members of the same species can breed together  Figure 15.12 number of families of hard shelled organisms which are preserved in earth’s fossil record  Background extinctions have declined, mass extinctions have increased  Living fossils: survived Permian and Cretaceous extinctions. Sharks and other chondrichthyans, trees, cyanobacterium Causes of Mass extinction Theories:  Plate Tectonics: figure 15.18, percent of the earth’s surface vs. sea level. If the sea level went down there would be less sea, and more land for things to live in, visa versa. Much of the continent is close to the sea level because the continent erodes to sea level. o Seafloor spreading centers: when volcanoes erupt more often in the ocean, the extra volume expands the floor as new oceanic crust is formed. Water is displaced and spills over continent o Glaciers: the bigger the glaciers, the lower the sea level. As glaciers melt, sea level rises o Continent size: the breakup of Pangaea lengthened the world’s shoreline and reduced harsh interior climates. One large landmass will have fewer species than several smaller ones, so breaking up of Pangaea spurred evolution o Polar Position: when land moves to the poles it can accumulate snow and begin and Ice Age  Volcanism – Lava pours out creating oceanic plateaus which raise the sea level o Atmospheric and Oceanic Chemistry changes – volcanoes release aerosols that change the atmosphere (make it warmer-GH effect) when they erupt. Poor correlation with mass extinction. Oceans absorb/dilute some of the gases, but the acidity level of the water can still change  Climate change – solar insulation, orbital cycles. Every environmental change has multiple climatic reactions. Ice Ages to Torrid Ages, change can happen faster than species can adapt  Ocean composition – circulation of oceans provides oxygen to organisms, if climate alters circulation patterns (water isn’t cold enough to sink and travel), the ocean bottom gets anoxic (depleted of oxygen) causing benthic species to become extinct. o Salinity levels- if glaciers melt (more freshwater) lowers ocean salinity; if water evaporates salinity levels rise  Extraterrestrial – supernova (stellar) explosion happens near to earth, nova, bursters, molecular cloud, impacts by asteroids/comets cause fires, tsunamis, acid rain, dust clouds (that block sunlight, raises temperature). Earth’s magnetic field diverts most of the incoming particles, but sometimes the field is weak and can cause mutations on earth (never proven)  Biological causes – epidemic disease, radical innovation, low population size, reduced geographical area, competition, and predation (
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