From Brian Gilligan

Methods of Thermal Energy Transfer

3. RADIATION

Heated objects radiate energy as well.

Methods of Thermal Energy Transfer

Convection is the most important mechanism for geologic processes.

Rock Types and the Rock Cycle

ROCK - a naturally occurring aggregate of mineralsformed within the Earth.

Delicate Arch, Arches Nat’l Park, UT

Basaltic DikeAcadia Nat’l Park,Maine

A MINERAL is anaturally occurring, inorganic solid, consisting of either a single element or compound,with a definite chemical composition (or varies within

fixed limits),and a systematic internal arrangement of atoms.

Rock Types and the Rock Cycle

DiamondC

PyriteFeS2

BerylBe3Al2(Si6O18)

Three types of rocks.These are present in the crust and at the Earth’s surface.Each have fundamentally different origin.

IGNEOUS

SEDIMENTARY

METAMORPHIC

Rock Types and the Rock Cycle

Igneous Rocks

- Cooled and solidified from MOLTEN material.- Formed either at or beneath the Earth’s surface.- MELTING of pre-existing rocks required.

Granite

BasalticLava

Sedimentary Rocks

- Pre-existing rocks are weathered and broken downinto fragments that accumulate and are thencompacted or cemented together.

- Also forms from chemical precipitates or organisms.

Metamorphic Rocks

- Form when pre-existing Earth materials are subjectedto heat, pressure and/or chemical reactionsand change the mineralogy, chemicalcomposition and/or structure of the material.

Coal

Gneiss

Slate

Any rock type can become any other rock type given time andprocesses acting on them.

These changes are reflected in the ROCK CYCLE.

Time and Geology

For most geologic processes a great deal a time is needed.

Earth is 4.6 billion years old.Time is available for these processes to operate very

slowly.

Geologists measure time in two ways:

1. RELATIVE AGE DATING

2. ABSOLUTE AGE DATING

Time and Geology

Relative Age Dating:- Determined by spatial relationships between adjacent

rock bodies and one another.- Provides relative age, no numbers involved.- Makes use of:

Principle of SuperpositionPrinciple of Cross-Cutting RelationshipsPrinciple of InclusionsPrinciple of Original Horizontality

Relative Age Dating:

Time and Geology

Time and Geology

Absolute Age Dating:- Determine actual age of the rock or structure.- Provides absolute age, actual numbers of years

are involved and applied.- Places rocks and events in Geologic Time Scale.

- Makes use of:

Radiometric techniquesTree-Ring Dating (Dendrochronology)Fission Track DatingLichenometry

Time and Geology

Absolute Age Dating:

GEOLOGIC TIME SCALE

- Subdivided into Era, Periods and Epochs- Based on fossil evidence, initially.- Actual years added using techniques mentioned

earlier.

The Theory of Plate Tectonics

Underlying unifying principle of geology.Evolved in the late 1960s, early 1970s.

Realization that certain parts of the Earth were moreaffected by earthquakes and volcanoes.

Also noted that large mountainous regions occur on margins of continents.

Changes in sea level were related to these events.

Was not a random occurrence.

Distribution of major volcanoes and earthquakes

The Theory of Plate Tectonics

Many hypotheses presented to answer these questions.

None answered all the questions at all localities.

Led to hypothesis of PLATE TECTONICS.

Became widely accepted in a few short decades.

The Theory of Plate Tectonics

Steps in Development

1. Benjamin Franklin (late 1700s)Recognized that crust of Earth was a shell.Surface could be broken and parts moved about.

2. Alfred Wegener (1912)German meteorologist-geophysicistProposed theory of Continental Drift.Proposed continents float on a denser

underlying interior of the Earth.CONTINENTS periodically break up and

DRIFT apart.

The Theory of Plate Tectonics

Wegener believed all continents were joined together.Supercontinent of Pangaea existed about 200 myBP.

Pangaea covered 40% of the Earth’s surface.