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16 Cards in this Set
- Front
- Back
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fossils
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Evidence of pre-existing life
Include preserved tracks, bones turned into rock, insects in amber, & imprints of shells Paleontology - the study of fossils Form when: Organisms die & become buried by sediment Organisms travel over or through sediment & leave their mark (trace fossils) |
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importance of fossils
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More than 250,000 species of fossils have been collected and identified
Fossils define the framework of life evolution on the planet Can be used to date strata Can be used to determine environmental conditions |
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fossil preservation
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Fossil Preservation
Death in an anoxic (oxygen-free) environment Oxidation reactions do not happen Scavenging organisms are not abundant Decay by bacteria takes along time Rapid burial Helps cut down on oxygen and scavenging Presence of hard parts Soft flesh decays long before hard parts Lack of metamorphism or erosion |
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rocks fossils survive in
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-sediments
-low-grade metamorphic -volcanic ash -rarely if ever occur in igneous rocks cept ash |
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different kinds of fossils
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Frozen or dried bodies (mummified)
Preserved in amber or tar Preserved or replaced bones, teeth, & shells Molds and casts Carbonized impressions Trace fossils |
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correlation
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Process of defining the age relationships between rocks at one locality and rocks at another
Often based on fossils |
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importance of fossils
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Still finding fossil sites
Not all organisms are represented in the rock record due to preservation potential Rock record provides an incomplete record of Earth history |
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index fossil
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Useful time indicators with:
Widespread geographic distribution Easy identification Short duration (of geologic time) |
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fossils and correlation
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Demonstration of time equivalency of rock units in different areas
Recognized by William Smith in the early 1800’s Trace laterally (principle of lateral continuity) Similarity of rock types & fossil content, especially index fossils Position in the sequence Key beds - marker horizon (ash beds & coal beds |
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extinctions
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Occurs when the last members of a species die
What causes extinction? Initially, thought large floods (catastrophism) Some occur suddenly, when all members of a species die off in a short time Others occur over longer periods, when death>> birth |
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what causes extinctions?
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Large numbers of species worldwide disappear
Reasons: Global climate change Tectonic activity Asteroid impact Appearance of a predator or competitor |
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late ordovician
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Late Ordovician
~ 1 m.y. span ~30% of families of marine invertebrates Due to global cooling (ice-age) & sea level decrease (decreases habitat) |
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late devonian
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Late Devonian
Several m.y. span 21% of families of marine invertebrates Due to global cooling (glaciation of Gondwana) & decrease in ocean temperature |
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late permian
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"mother of all mass extinctions"
Late Permian ~10 m.y. span 95% of families of marine invertebrates ~70% of land vertebrates Due to… Pangea? Restricted ocean circulation Volcanism? Siberian Traps |
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late triassic
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20% of families of marine invertebrates
Paved the way for Dinos Due to ????? Pangea Breakup? |
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late cretaceous
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Late Cretaceous (K-T boundary)
~30% of marine invertebrates ~60% of N.A. Plants Killed off dinosaurs Due to: Bolide Impact Chicxulub (Yucatan) 180 km crater, >10 km meteor Terrestrial Deccan Traps Decrease in sea level |
