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Geologic time

Geologic Time

A method of ordering and measuring past events

How old is this photograph
How Old is this Photograph?

  • How can

    you tell?

  • What

    are some


Geologic time

Geologic time

  • Longest unit of geological time

  • Measured in billions of years

  • Present eon: Phanerozoic

Geologic time

  • Second longest geological time measurement

  • Hundreds of millions of years

  • Present era: Cenozoic


  • Third longest geological time measurement

  • Measured in tens of millions to hundreds of millions of years

  • Defined by the life forms that were abundant or became extinct

  • Present: Quaternary


  • Fourth geological time measurement

  • Measured in million to tens of million of years

  • Present epoch: Holocene

Geologic time

Relative dating
Relative Dating

  • Determines the order in which geological events occurred based on stratigraphic principles, fossils and bands of rock

Absolute dating
Absolute Dating

  • Provides a numerical age for the material tested

The principle of superposition
The Principle of Superposition

The principle of original horizontality
The Principle of Original Horizontality

The principle of lateral continuity
The Principle of Lateral Continuity

The principle of cross cuttining
The Principle of Cross-cuttining

The principle of intrusion inclusion
The Principle of Intrusion/Inclusion

Principle of deformation unconformity
Principle of Deformation/Unconformity

Correlation similar rock patterns
Correlation: Similar Rock Patterns

Correlation fossils
Correlation: Fossils

Geologic time

Absolute dating techniques
Absolute Dating Techniques

Geological records with strong annual cyclicity
Geological Records with Strong Annual Cyclicity

  • Tree growth rings

  • Coral growth rings

  • Varves (annual clay sediment layers)

Geologic time

Coral annual ring growth
Coral Annual Ring Growth


Radiometric dating
Radiometric Dating

  • Methods relying on the decay of naturally occurring radioisotopes

Most common radioisotope decay
Most Common Radioisotope Decay

  • Carbon-14 -> Nitrogen-14

  • Potassium-40 -> Argon-40

  • Uranium-235 -> Lead-207

  • Uranium-238 -> Lead-206

  • Thorium-232 -> Lead-208

  • Rubidium-87 -> Strontium-87