How The Earth Works
The Solid Earth
Earth Science
• Geology
– Solid Earth Much Larger than Other Parts
– Many More Kinds of Materials
– Preserves a History
• Meteorology – Climatology
• Oceanography
• Astronomy
– Planetary Geology
Earth Systems
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External Effects (Astronomical)
Atmospheric Circulation
Oceanic Circulation
Hydrologic Cycle
Rock Cycle
Plate Tectonics
Convection
Earth and the Universe
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Rotation (Day-Night)
Lunar (Tides)
Annual (Seasons)
Precession and Orbit Variations (Ice Ages?)
Galactic (250 m.y. period)
Unpredictable Events
– Nearby Supernovae
– Meteor Impacts
• Long-Term Evolution of Sun
Atmospheric Circulation
• Unequal Solar Heating
– Equator to Pole
– Day - Night
– Different Surfaces
• Buoyancy
• Adiabatic Heating and Cooling
• Coriolis Effect
• High and Low Pressure
• Fronts and Air Masses
Atmospheric Circulation
Oceanic Circulation
• Surface Currents - Driven by Winds
• Thermohaline - Deep Circulation
– Evaporation makes water more saline and
denser
– Freezing makes water more saline and denser
– Cold water is denser than warm water
Surface Currents
Thermohaline Circulation
Hydrologic Cycle
• Evaporation from Oceans
• Precipitation on Land
– Infiltration into Ground (Ground Water)
– Runoff (Erosion)
Hydrologic Cycle
Water
• Principal Agent in Modifying Earth’s
Surface
• Medium for Storing and Distributing Global
Heat
• The Universal Solvent
– Essential for Life
– Destructive to Rocks
• Lowers Melting Point of Rocks
• Reduces Strength of Rocks Under Pressure
The Rock Cycle
• New Rocks Exposed by Erosion
• Rocks Broken Down Mechanically and
Chemically (Weathering)
• Components Transported by Erosion
• Components Cemented into Sedimentary Rocks
• Burial and Heating creates Metamorphic Rocks
• Melting Creates Igneous Rocks
The Rock Cycle
Plate Tectonics
• Outer Crust of Earth Moves a Few cm/yr
• Driven by Convection in Earth’s Interior
• Accounts For:
– Earthquakes
– Volcanoes
– Mountain-Building (Orogeny)
• Configuration of Continents
Plate Tectonics
Plate
Tectonics
and
Resources
Configuration of Continents
• Oceanic Circulation
• Weather and Climate Patterns
– Deserts
– Mountains and Rain Shadows
• Pathways for Migration
• Ecological Niches
Configuration of Continents
Some Unique Aspects of
Geology
Importance of Relationships
• Sequential
• Spatial
Importance of Time
Distinctive Problems of Evidence
• Slow Rates
• Rare Events
• Destruction of Evidence
• Inaccessibility
Some Geologic Rates
Cutting of Grand Canyon
• 2 km/3 m.y. = 1 cm/15 yr
Uplift 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.
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.
1 Second = 1 Year
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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
Some Unique Aspects of
Geology (Continued)
Reliance on Inference and Deduction
Intrinsically "Unsolvable" Problems
• Ancient Landscapes
• Mass Extinctions
• Ancient Ocean Basins
Scientific Principles in Geology
• Parsimony (K.I.S.S.)
• Superposition
• Uniformitarianism
Using these, plus observation, we establish
facts about Earth Processes
Parsimony
• The simplest explanation that fits all the
data is preferred
• Doesn’t guarantee that things must be
simple!
• Theories with lots of ad hoc or unsupported
ideas are probably wrong.
Superposition:
Mindoro Cut,
Wisconsin
Geologic
Map
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 Uniformitarianism