Chapter 6

Chapter 6 - Chapter6 18:40 Fossils

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Chapter 6 18:40 Fossils Remains or traces of ancient life which have been preserved by natural  causes in the Earth’s crust Marine and transitional environments are more favorable for fossil  preservation. Higher rate of sediment deposition o In order to become a fossil Need hard preservable parts- bones, shells, teeth, wood Be buried by sediment- protect from scavengers and decay Escape physical, chemical and biological destruction Types of Fossil preservation Chemical alteration of hard parts o Permineralization- filing of tiny pores It occurs when water that contains dissolved silica, calcium carbonate,  or iron circulates through the sediment that encloses a deceased  organism. The minerals become deposited in the organism remains.  Original composition of the bone or shell remains but the fossil is made  harder and more durable by the minerals. Replacement- molecule by molecule substitituion of one mineral for another o Is the simultaneous exchange of the original substance of a dead plant or  animal with mineral matter of a different composition. Solutions dissolve  the original material and replace it with an equal volume of the new  minerals. Recrystallization- aragonite alters to calcite Carbonization- soft tissues preserved as a thin carbon film (ferns in shale) Imprints of hard parts in sediment o Impressions External mold Internal mold Mold means
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After burial the object disintegrates leaving a void where the  organism was. Shows the surface imprint of the original just  inside the shell. casts Preservation of unaltered soft parts o Freezing o Desiccation- drying o Preservation in amber o Preservation in tar o Preservation in peat bogs Trace fossils or inchofossils- markings in the sediment made by the activities  of organisms o Trace fossils Provide infiromation about ancient water depths,  paleocurrents, availability of food, and sediment depostion rates o Tracks provide info on foot structure, number of legs, leg length speed,  herding behavior, and interactions Tracks, trails, burrors (soft sediment), borings (hard material), root  marks, nests, eggs, coprolites (poop), bite marks Preservation of unaltered hard parts o Calcite o Aragonite o Phosphate o Silica o Organic matter Petrifaction To make into stone by sediment burying the fossil
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Biological classification A system of binomial nomenclature- two names used to name organism Species Group of organisms that have structural developmental similarities and that  are able to interbreed and produce fertile offspring Fundamental unit of biological classification Different species do not interbreed under natural conditions. Reproductive 
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This note was uploaded on 09/28/2009 for the course GEOL 002 taught by Professor Brown during the Fall '09 term at GWU.

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Chapter 6 - Chapter6 18:40 Fossils

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