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Earth’s “Spheres”

Atmosphere

Hydrosphere

Lithosphere

Biosphere

= The EarthSystem

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Some Fundamental Principles

The universe is regular, predictable and

quantifiable

Earth’s surface is constantly changing

Everything on Earth operates in cycles

All life forms evolved by natural selection

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Key Factors in Earth’s Evolution

After partial melting, it remains hot insidedue to energy from radioactive elements.

The distance from the Sun and Earth’snatural “greenhouse” allow liquid water to bepresent.

Development of a Biosphere.

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A Force: Gravity -The Great Leveler

Related to product of masses (m x m) andinversely to distance squared

Weight = mass x g (i.e., weight ≈ mass)

At Earth’s surface, all motion is due togravity

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An Energy - Heat

“Transfer of energy resulting fromtemperature differences”

Bodies at same T are in thermal equilibrium

Sources of heat: internal and external

Internal - radioactive decay; cooling ofinterior

External - sun (also source of light energy)

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Sources of Interior Heat

Cooling of Earth from its original molten state

Decay of radioactive elements

Major ones are U, Th, K, Rb

One element is converted to another

(Ex. U => Pb)

An energetic particle and heat are released

Same principle as the atomic bomb

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Transfer of Heat

Convection - transfer by flow of fluid ormolten material

Conduction - transfer through a solid

Radiation - transfer through air, liquid orvacuum

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Most objects expand when heated

Decreases density (less mass per unit volume)

Density changes cause fluids to move

Less dense rises; denser sinks

Hot air rises; cold air sinks

Heat also causes phase changes (water to vapor)

Salt content also affects density

Heat and Density

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Gravity and Density

All movements via density changes areaffected by gravity

Objects becoming cooler (i.e., denser) thantheir surroundings will sink

Objects becoming warmer (i.e., less dense)than surroundings will rise

Phase changes are density changes andare affected by gravity

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Natural Energy Sources

Earth's Interior

Sun

HEAT

HEAT AND LIGHT

Biol.Prod.

CurrentsWavesWind

Evap.

ExternalEnergy

InternalEnergy

Buildsmountains

Destroysmountains

Fusion Energy

Fission Energy

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How did Earth become density stratified?

• Young Earth was probably homogeneous

• Heat and gravitational pressure caused Earth to partiallymelt

• Gravity then pulled iron and other heavy elements into thecenter of Earth, heating the planet further

• Lighter minerals migrated to Earth’s surface and formedthe crust

Earth’s Layers

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Density stratificationresults in an inner andouter core, a mantleand crust.

The Formation Of Earth

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• Earth’s lost its first atmosphere

• Gases, including water vapor, released by the process ofoutgassing, replaced the first atmosphere.

• Water vapor in the atmosphere condensed into clouds.

• After millions of years, the clouds cooled enough for waterdroplets to form.

• Hot rain fell and boiled back into the clouds.

• Eventually, the surface cooled enough for water to collectin basins.

Where did Water Come From?

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17The early atmosphere was very different from the atmosphere today.

The Early Atmosphere

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How old is the Earth, and how do weknow it?

Rocks can be dated by measuring the rateof radioactive decay of certain elements.

The oldest objects found on Earth aremeteorites that are about 4.6 b.y.

Lunar rocks are also this age.

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A Timeline Of Earth’s History

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Figure 1.6

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GlobalPositioning

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Figure 1.8

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Figure 1.15

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Figure 1.16

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Figure 1.10

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Figure 1.19

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Figure 1.21

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Figure 1.22

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