EASC1402-1A-17 Geological Time Part 2.pptx

EASC1402-1A-17 Geological Time Part 2.pptx - SC1402...

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Geological Time Scales & Dating: Part 2 (Absolutely!) November 21 st 2016 - Dr. Jess King ([email protected]) ASC1402 Principles of Geology
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To develop a geological time scale for the entire Earth, rocks of a similar age in different regions must be matched up… Easy enough on a basin scale – Original Horizontality & Continuity… but what about globally??? This task is called Correlatio
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Where Fossils Occur Almost Exclusively in Sedimentary Rocks Heat of Melting or Metamorphism Would Destroy Almost Every Type of Fossil Rare Exceptions: Some Fossils in Low-grade Metamorphic Rocks, but these are often distorted, hard to interpret Trees Buried by Lava Flow To Be Preserved, Organisms Have to Be: Buried Rapidly After Death Preserved From Decay ASC1402 Principles of Geology
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Body fossils Macrofossils : e.g. bones, plants Microfossils : e.g. diatoms, planktons Nanofossils (<10 microns): e.g. bacteria Trace fossils Figure 9.16d Figure 9.16f ASC1402 Principles of Geology Fossils – 2 types:
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How are Fossils Formed? About 67 million years ago -- A Tyrannosaurus rex died and its body was quickly covered by riverbed sand and mud. Over time, pressure and some remineralization turned its bones to fossils. ASC1402 Principles of Geology
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Fossil Formation Very rare – particularly large specimens Must remain stationary for many years Mostly hard parts Teeth, bones, shells Rarely soft parts Jellyfish, worms, skin Must be buried away from oxygen to fossilize – i.e. can’t decompose Volcanic ash, tar pit, mudslide, marine snow, anoxic muds Marine Carbonate (CaCO 3 ) somewhat easier as long as the organism is within the calcite saturation zone = Limestones ASC1402 Principles of Geology
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Types of Fossil Preservation: Preserved remains: Frozen in ice, trapped in amber Mineral replacement
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