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Introduction to Geology

Study ofEarth

Science 330 Summer 2005

Geology

From the Greek:

Geo(“Earth”), and

Logos(“Discourse on”, or “Study of”)

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Broad Divisions of Geology

Physical Geologyexamines the materials and processes at work within

the earth

Historical Geologystudies the origin of earth and development through

time

“Environmental Geology”

December 26, 2004

Sumatran Earthquake /

Tsunami

TITOV-INDO2004.mov

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“Environmental Geology”

La Conchita, 1995

People were warned, evacuated,

none killed

January 10, 2005

Not so lucky…

History of Geology

Catastrophism – landscapes have been influenced by great catastrophes

Popular during 18th and 19th centuries

Uniformitarianism – “present is the key to the past”

Advanced by Hutton (“Father of Geology”) in the late 1700’s, and Lyell in the 1800’s

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Catastrophism ?

Velikovsky (1950’s) – Venus a “comet” ejected from Jupiter

W. & L. Alvarez (1980) –asteroid struck Earth 65 Ma, caused dinosaur extinction

The debate continues…

Relative dating

Geologic Time Scale – developed in the 19th centuryLaw of Superposition – in sediments, most recent is on topPrinciple of fossil succession –organisms change in an orderly fashion

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Relative dating

Relative dating

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Relative dating

The Scientific Method

Assumption –universe behaves in a consistent and predictable fashion that is comprehensible through careful, systematic study

Goal –discover underlying patterns, make predictions

The Process –gather facts and formulate scientific hypotheses and theories ( = The Scientific Method )

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The Scientific Method

1. Collect facts2. Develop a scientific hypothesis3. Construct experiments to test the

hypothesis4. Accept, modify, or reject the

hypothesis on the basis of extensive testing

Earth’s Four Spheres:

Hydrosphere – dynamic mass of waterocean blankets 71% of surface to average depth of 3800 meters (97% of earth’s water)

Atmosphere – life-giving gaseous envelope

half below an altitude of 5.6 km, 90% less than 16 km

Biosphere – all life on Earthconcentrated near the surface

Solid Earth – bulk of mass of the Earthradius of 6400 km

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Earth as a System:

System –Group of interacting, or interdependent, parts that form a complex whole

Sources of Energy:

The Sun –Drives the external processes that occur in the atmosphere, hydrosphere, biosphere, and at the surface

Heat from the earth’s interior –

Powers the internal processes that produce volcanoes, earthquakes, and mountains

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The Rock

Cycle:

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Continents and Ocean Basins

The continental shelf and continental slope mark the continent-ocean basin transition

Continental Features

Mountains

Shields

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Continental Features

Mountains (Sierra Nevada, looking west)

Continental Features

Mountains (Sierra Nevada, looking west)

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Edge of the Canadian Shield(North Dakota)

Medicine Bow Mountains, Wyoming

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Oceanic Features

Trenches and Ridges

Oceanic Features

Earthquake Concentrations, recognized in 1954

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Oceanic Features

Mid-Ocean Ridge System

Oceanic Features

Distribution of Deep-Sea Sediments

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Oceanic Features

Oceanic Crustal Ages

Nebular HypothesisDescribes the birth

of the Solar System

Enormous rotating cloud:

solar nebula

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Nebular Hypothesis

Planets and Sun began forming ~ 5 Ga from the solar nebula, a large rotating cloud of dust and gases (mostly H and He)

Nebular Hypothesis

The cloud contracted, began to rotate and assume a disk shape (steps A to B)

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Nebular Hypothesis

Material pulled toward the center created the PROTOSUN (middle of C)

Nebular Hypothesis

Small centers, called PROTOPLANETS (dots in C) swept up more and more of the cloud’s debris

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Nebular Hypothesis of Solar System Formation

Nebular Hypothesis

Inner planets – high temp’s, weak gravitational fields, unable to grab lighter elementsOuter planets – colder, huge amounts of lighter elements

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Internal Structure of Earth

Divided into layers based on:

1. Composition2. Physical

properties

Internal Structure of Earth

(cont.)

Compositionally:

1. Thin outer CRUST2. Solid rocky MANTLE3. Dense CORE

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Internal Structure of Earth (cont.)

Based on Physical Properties:

1. LITHOSPHERECool, rigid outermost layer (~100 km)

2. ASTHENOSPHERE“weak zone” – in the mantle below lithosphere

3. MESOSPHEREMore rigid than asthenosphere, very hot, capable of

gradual flow

4. OUTER CORELiquid, where magnetic field is generated

5. INNER CORESolid

Plate Tectonics

A comprehensive model of Earth’s internal workings

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Plate Tectonics

Lithosphere consists of numerous segments (plates), continuouslymoving with respect to each other

Plate Tectonics

Earthquakes

Volcanic activity

Mountain building

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Plate Tectonics

Types of plate boundaries:

Divergent boundariesPlates move apart – oceanic ridge

Convergent boundariesPlates move together – subduction zone or collision zone

(i.e., Himalayas)

Transform Fault boundariesPlates slide past one another – San Andreas Fault

Divergent Boundaries

Spreading centers, such as a mid-ocean ridge

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Divergent Boundaries

Salton Buttes: spreading center under land

Convergent Boundaries

Continent-Continent Collision

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Convergent Boundaries

Continent-Continent Collision

Convergent Boundaries

Subduction Zones, or Ocean-Continent Collision

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Transform Fault Boundaries

Less Volcanism, More Earthquakes

End of Introduction to Geology