Rock and Fossil Record

  James Hutton: 1788 wrote a book with a big idea  Uniformitarianism -same processes long ago are the same as today  Controversial because it contradicted catastrophism  However, Lyell supported Hutton and used his notes to win the battle  Today though we believe that both play an important role in shaping Earth 6.1: Earth’s Story

  Paleontology :  The study of past life  Came about because of the new idea of how Earth is much older than we believed Specific Studies

  Scientists try to determine when events happened on Earth  They use relative dating : is determining whether an object is older or newer than the other objects around it  They use the law of superposition to help answer the question  Old on bottom, young on top  However, this can be altered by Earth’s forces 6.2: Relative Dating

  The Geologic Column :  An ideal sequence of rock layers that contain all the known fossils and rock layers of Earth  Helps when rock layers are disturbed  Can happen from folding or tilting A valuable tool

  Gaps in the geologic record (can be millions of years)  Can be for 2 reasons:  1.) Never existed  2.) Sediments quit filling in the area  3 types:  1.) Disconformity : part of layer is missing  Most common  2.) Nonconformity : sedimentary rock layer on top of older igneous rock layer  3.) Angular Unconformity : rock layers tilted or folded Unconformities:

 Unconformities

  Estimates the number of years a fossil or rock has been in existence  Must use isotopes : same protons, different neutrons  Some are unstable and radioactive (these break down to stable elements) 6.3: Absolute Dating

  You must know the rate of decay of the isotope  You use math to determine the ratio  Half-life: time it exists for ½ of isotope to decay and become stable  Every isotope has a different half-life Radiometric Dating

  1.) Potassium-Argon  ½ life of 1.3 billion years  Used to date old rocks  2.) Uranium-Lead  ½ life 4.5 billion years  Dates really old rocks  3.) Rubidium-Strontium  ½ life 49 billions years  Dates the oldest rock  4.) Carbon-14  ½ life 5,730 years  Dates things within 50,000 years Types of Radiometric Dating

  Fossil : preserved remain of an organism by geological processes  Preserved by:  1.) Rock  2.) Amber (Jurassic Park)  3.) Petrifaction (petrified wood)  4.) Tar Pits (asphalt)  5.) Ice (Wooly mammoth, Ice-man) 6.4 Fossils

  Trace Fossils :  Preserved remains of anima activity  Ex.) Coprolite (Animal dung)  Molds and Casts:  Mold is an area where an animal was buried  Cast is where sediment has filled in a mold Other Types of Fossils:

  Many uses:  Environmental change  Ex.) North Dakota Oil Fields  History of changing organisms  Ex.)Dinosaurs  todays reptiles  Dating rocks  Index fossils : lived short time but in a definite geologic time  Ex.) Trilobites ~400mya Fossil Uses:

  Divisions of Time:  We go from large  small  1.) Eons : 4 of them  2.) Eras : 3 in the Phanerozoic eon  3.) Periods : divisions of Eras  4.) Epochs : divisions of periods 6.5 Time

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  In Earth’s history species have come and gone  Extinction : death of every member of a species  Ex.) Dinosaurs-Mesozoic Era extinction  Ex.) Mammals-Cenozoic Era extinction  Tasmanian Tiger, Dodo Bird, Saber tooth tiger Species come and go