How The Earth Works

The Solid Earth

Earth Systems

• External Effects (Astronomical)

• Atmospheric Circulation

• Oceanic Circulation

• Hydrologic Cycle

• Rock Cycle

• Plate Tectonics

Convection

Earth and the Universe• 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 TimeDistinctive Problems of Evidence• Slow Rates • Rare Events • Destruction of Evidence • Inaccessibility

Some Geologic RatesCutting 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.

Some Geologic RatesMovement 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• 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