102 Earth History 1

8/12/2019 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

102 Earth History 1

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