The Geologic Time Scale

Geologic Time Scale

Geologic Time Scale:

Subdivisions of Earth's history

• by pure Time and

• by Rocks deposited during an interval of time

Geologic Time Scale

Divisions:

Eons (largest)

Phanerozoic------ “shelly fossils” 542 my

Proterozoic------ modern tectonics 2.5 by

Archean------ oldest rocks 4.0 by

Hadean ------ origin of Earth 4.6 by

Geologic Time Scale

Geologic Time Scale

“Precambrian” is an informal term for everything prior to the Cambrian

Divisions:

Eras

• only Phanerozoic subdivided

• based on appearance of fossils

• bounded by mass extinctions

Geologic Time Scale

Divisions:

Eras (largest)

Cenozoic - new life

Mesozoic - middle life

Paleozoic - ancient life

Geologic Time Scale

Periods (fundamental unit)

• Geologic column originally divided as Time-Rock units.

Geologic Time Scale

Periods (fundamental unit)

• Geologic Time units bear the names

of their corresponding Time-Rock units.

Geologic Time Scale

Time Scale was developed piece-meal

• Units were recognized locally

• Bounded by regional unconformities

• Based on fossil assemblages

• Named for local geography (tribes)

Geologic Time Scale

Geologic Time Scale

19th CNaturalists

Characterizedtheir own rocks

Geologic Time Scale

19th CNaturalists

Characterizedtheir own rocks

“Wataugan”

“Catawbian”

“Allegheny”

Type section: where the unit was originally defined.

• Independent workers

• Around Europe

• 19th Century

Geologic Time Scale

Type sections:

Geologic Time Scale

Cambrian

Ordovician

Devonian

Silurian

Time scaleassembled by:

Geologic Time Scale

• Principle of Superposition• Principle of Fossil Succession

• Correlation

Characteristics of the Time Scale:

• There is not a single, complete section anywhere!

• Scale was originally all relative.

• Absolute time was added later.

Geologic Time Scale

Same principles applied forEpochs & Ages

• Biologic component more important

• Cenozoic Epochs were originally based on % of modern mollusc species.

• Work on Series & Stages continuestoday

Geologic Time Scale

What to know.

Geologic Time Scale from class web pagePractice on Blank

• Eons (dates) • Eras (for Phanerozoic & dates) • Periods (Miss, Penn, & Tertiary) • Do not have to know who, where & when

of naming.

Geologic Time Scale

What to know.

Geologic Time Scale from class web pagePractice on Blank

• Eons (dates) • Eras (for Phanerozoic & dates) • Periods (Miss, Penn, & Tertiary) • Do not have to know who, where & when

of naming.

Geologic Time Scale

My personal guaranteeQuestion #1 on Test 1

QueensTwoCoverJacksThreePokerPlayMaybeDaySomeOverCome

HoneyPleasePlateMyOnEggsPut

Grand Canyon Zion

Complete Geologic Section can beassembled though correlation.

For example: Arizona - Utah

Bryce Canyon

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Cambrian - Jurassic

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Brice CanyonZion

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Zion

Cambrian - Quaternary

Bryce Canyon