geology
Telling Geologic Time
Putting it in perspective
Determining geological ages
• Relative age dates – placing rocks and events in their proper sequence of formation
• Numerical dates – specifying the actual number of years that have passed since an event occurred (known as absolute age dating) Figure 1-15 (p. 16)
Geologic Time Scale.
Uniformitarianism
The physical, biological and chemical principles acting on the Earth in the present also acted on the
Earth in the past.
Getting Dates
Relative Dating
Law of Superposition
• Developed by Nicolaus
Steno in 1669
• In an undeformed sequence of sedimentary rocks (or layered igneous rocks), the oldest rocks are on the bottom
Superposition in the Grand Canyon
Principles of relative dating
• Principle of original horizontality
• Layers of sediment are generally deposited in a horizontal position
• Rock layers that are flat have not been disturbed Original Horizontality (d)
Lateral Continuity (e)
Figure 1-6 (p. 5)
Illustration of original lateral continuity.
Law of Cross-cutting
Relationships
Inclusions
•An inclusion is a piece of rock that is enclosed within another rock
•Which layer is younger?
Inclusions
Baked Contacts
Contact Metamorphism
Lava flow
Geologic History
• A cross-section through the earth reveals the variety of geologic features. View 1 of this animation identifies a variety of geologic features; View 2 animates the sequence of events that produced these features, and demonstrates how geologists apply established principles to deduce geologic history. [by Stephen
Marshak]
• Play Animation Windows version >>
• Play Animation Macintosh OS9 version >>
• Play Animation Macintosh OSX version >>
Gaps in the Record:
Unconformities
Angular unconformity, Siccar Point, Scotland
Erosional Surfaces
• Unconformities represent gaps in the geologic record because of surface erosion
Figure 1-8 (p. 8)
Putting it in perspective
Determining geological ages
• Relative age dates – placing rocks and events in their proper sequence of formation
• Numerical dates – specifying the actual number of years that have passed since an event occurred (known as absolute age dating) Figure 1-15 (p. 16)
Geologic Time Scale.
Uniformitarianism
The physical, biological and chemical principles acting on the Earth in the present also acted on the
Earth in the past.
Getting Dates
Relative Dating
Law of Superposition
• Developed by Nicolaus
Steno in 1669
• In an undeformed sequence of sedimentary rocks (or layered igneous rocks), the oldest rocks are on the bottom
Superposition in the Grand Canyon
Principles of relative dating
• Principle of original horizontality
• Layers of sediment are generally deposited in a horizontal position
• Rock layers that are flat have not been disturbed Original Horizontality (d)
Lateral Continuity (e)
Figure 1-6 (p. 5)
Illustration of original lateral continuity.
Law of Cross-cutting
Relationships
Inclusions
•An inclusion is a piece of rock that is enclosed within another rock
•Which layer is younger?
Inclusions
Baked Contacts
Contact Metamorphism
Lava flow
Geologic History
• A cross-section through the earth reveals the variety of geologic features. View 1 of this animation identifies a variety of geologic features; View 2 animates the sequence of events that produced these features, and demonstrates how geologists apply established principles to deduce geologic history. [by Stephen
Marshak]
• Play Animation Windows version >>
• Play Animation Macintosh OS9 version >>
• Play Animation Macintosh OSX version >>
Gaps in the Record:
Unconformities
Angular unconformity, Siccar Point, Scotland
Erosional Surfaces
• Unconformities represent gaps in the geologic record because of surface erosion
Figure 1-8 (p. 8)