102 earth history 1
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Geologic
Time andEarth
History
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Two Conceptions of Earth History:
Catastrophism Assumption: Great Effects Require Great Causes Earth History Dominated by Violent Events
Uniformitarianism Assumption: We Can Use Cause And Effect to
Determine Causes of Past Events
Finding: Earth History Dominated by Small-scaleEvents Typical of the Present. Catastrophes Do Happen But Are Uncommon
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Uniformitarianism
Continuity of Cause and Effect Apply Cause and Effect to Future -
Prediction Apply Cause and Effect to Present -
Technology Apply Cause and Effect to Past
UniformitarianismThe Present is the Key to the Past
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Ripple Marks, Bay Beach
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Fossil Ripple Marks, Baraboo Range
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Modern Mud Cracks
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Fossil Mud Cracks, Virginia
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Two Kinds of Ages
Relative - Know Order of Events But NotDates
Civil War Happened Before W.W.II
Bedrock in Wisconsin Formed Before TheGlaciers CameAbsolute - Know Dates
Civil War 1861-1865 World War II 1939-1945 Glaciers Left Wisconsin About 11,000 Years
Ago
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Superposition:Mindoro Cut,
Wisconsin
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GeologicMap
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Fossils
Remains of Ancient Plants AndAnimals, Evidence of Life
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Commonly Preserved:
Hard Parts of Organisms: Bones Shells Hard Parts of Insects Woody Material
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Rarely PreservedSoft or Easily Decayed Parts of Organisms: Internal Organs
Skin Hair Feathers
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Types of Fossils
Original Material Casts & Molds
Replacement (Petrified Wood) Carbonized Films (Leaves) Footprints, Tracks, Etc.
Trace Fossils Our only preserved record ofbehavior of fossil organisms
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DinosaurTracks,Texas
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RubbingRock?
Wisconsin
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RubbingRock?
California
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Pseudofossils
Look Like Fossils But Aren't Dendrites Concretions
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Pseudofossils
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Natural or Sculpture?
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Johannes Beringers Fossils
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Beringers
Book
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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 Trees Buried by Lava Flow
To Be Preserved, Organisms Have to Be: Buried Rapidly After Death Preserved From Decay
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Fossil Tree in Lava Flow, Hawaii
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Good Index Fossils
Abundant Widely-distributed (Global Preferred) Short-lived or Rapidly Changing
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Correlation
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The Geologic Time ScaleQuaternary Latin, fourth 1822
Tertiary Latin, third 1760
Cretaceous Latin creta , chalk 1822
Jurassic Jura Mountains, Switzerland 1795
Triassic Latin, three -fold 1834Permian Perm, Russia 1841
Carboniferous Carbon-bearing 1822
Devonian Devonshire, England 1840Silurian Silures , a pre-Roman tribe 1835
Ordovician Ordovices , a pre-Roman tribe 1879
Cambrian Latin Cambria , Wales 1835
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Absolute Ages: Early Attempts
The Bible Add up Dates in Bible Get an Age of 4000-6000 B.C. For Earth John Lightfoot and Bishop Ussher - 4004
B.C. (1584) Too Short
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Absolute Ages: Early Attempts
Salt in Ocean If we know rate salt is added, and how much salt
is in ocean, can find age of oceans.
Sediment Thickness Add up thickest sediments for each period,
estimate rate.
Both methods gave age of about 100 million years Problem: Rates Variable
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Age of The Sun If sun gets its heat from burning or other chemical
reactions, could only last 10,000 years or so. Best 19th century guess: sun was slowly
contracting. Problem: only 30 million years ago, sun would
have extended out to earth's orbit! Geologists wanted more time, but you can't fight
the laws of physics... Sun actually gets its energy from nuclear
reactions and can keep going for billions of years The Geologists were right after all. Go Team.
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The Fundamental Rule ofAbsolute Ages
The Earth is older than everything on or in it-Except its atoms
-All ages are minimum ages
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Radiometric Dating: Half-Life
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Present Radiometric Dating Methods
Cosmogenic C-14 5700 Yr.Primordial K-Ar (K-40) 1.25 B.Y. Rb-Sr (Rb-87) 48.8 by U-235 704 M.Y.
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The
GeologicTime Scale
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Some Geologic Rates
Cutting of Grand Canyon 2 km/3 m.y. = 1 cm/15 yrUplift of Alps 5 km/10 m.y. = 1 cm/20 yr.Opening of Atlantic 5000 km/180 m.y. = 2.8 cm/yr.
Uplift of White Mtns. (N.H.) Granites 8 km/150 m.y. = 1 cm/190 yr.
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Some Geologic Rates
Movement of San Andreas Fault 5 cm/yr = 7 m/140 yr.Growth of Mt. St. Helens 3 km/30,000 yr = 10 cm/yr.Deposition of Niagara Dolomite 100 m/ 1 m.y.? = 1 cm/100 yr.
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1 Second = 1 Year 35 minutes to birth of Christ 1 hour+ to pyramids 3 hours to retreat of glaciers from Wisconsin 12 days = 1 million years 2 years to extinction of dinosaurs 14 years to age of Niagara Escarpment 31 years = 1 billion years
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Were The Dinosaurs Failures?Dinosaurs: 150,000,000 yearsRecorded History: 5000 years For every year of recorded history, the
dinosaurs had 30,000 years For every day of recorded history, the
dinosaurs had 82 years For every minute of recorded history, the
dinosaurs had three weeks