Earth’s “Spheres”
Atmosphere Hydrosphere = The Earth System Lithosphere Biosphere
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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 inside due to energy from radioactive elements.
The distance from the Sun and Earth’s natural “greenhouse” allow liquid water to be present.
Development of a Biosphere.
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A Force: Gravity - The Great Leveler
Related to product of masses (m x m) and inversely to distance squared
Weight = mass x g (i.e., weight ≈ mass)
At Earth’s surface, all motion is due to gravity
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An Energy - Heat
“Transfer of energy resulting from temperature differences”
Bodies at same T are in thermal equilibrium
Sources of heat: internal and external
Internal - radioactive decay; cooling of interior
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 or molten material
Conduction - transfer through a solid
Radiation - transfer through air, liquid or vacuum
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Heat and Density
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
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Gravity and Density
All movements via density changes are affected by gravity
Objects becoming cooler (i.e., denser) than their surroundings will sink
Objects becoming warmer (i.e., less dense) than surroundings will rise
Phase changes are density changes and are affected by gravity 10
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Natural Energy Sources
Fusion Energy External Sun Energy
HEAT AND LIGHT Destroys mountains
Biol. Currents Evap. Prod. Waves Wind Builds mountains HEAT Internal Energy Earth's Interior Fission Energy 13
Earth’s Layers How did Earth become density stratified?
• Young Earth was probably homogeneous
• Heat and gravitational pressure caused Earth to partially melt
• Gravity then pulled iron and other heavy elements into the center of Earth, heating the planet further
• Lighter minerals migrated to Earth’s surface and formed the crust
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The Formation Of Earth
Density stratification results in an inner and outer core, a mantle and crust.
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Where did Water Come From?
• Earth’s lost its first atmosphere
• Gases, including water vapor, released by the process of outgassing, replaced the first atmosphere.
• Water vapor in the atmosphere condensed into clouds.
• After millions of years, the clouds cooled enough for water droplets to form.
• Hot rain fell and boiled back into the clouds.
• Eventually, the surface cooled enough for water to collect in basins. 16
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The Early Atmosphere
The early atmosphere was very different from the atmosphere today. 17
How old is the Earth, and how do we know it?
Rocks can be dated by measuring the rate of radioactive decay of certain elements.
The oldest objects found on Earth are meteorites 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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Global Positioning
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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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