Unformatted text preview: Deep Time: How Old is Old? Age of the Earth - A Historical Perspective
Age Catastrophism Uniformitarianism Mud cracks now...
Mud ... and mud cracks then Siccar Point, Scotland
Point, Sedimentation of beds beneath the sea
Sedimentation Deformation and erosion during mountain building
Deformation Erosional surface cuts across deformed rocks
Erosional Subsidence and subsequent deposition
buries erosional surface Age of
diversification Fig. 12.24
W. W. Norton
Geologic time scale Unicellular life Two ways to date geologic events
Two Absolute time and Radiometric Dating
Absolute Break down
Break W. W. Norton Radioactive decay and half-lives
β– Radioactive decay schemes
• 232Th-208Pb 87Rb
87 half-life 48 Ga
half-life 106 Ga
half-life 4.5 Ga
half-life 0.7 Ga
half-life 14 Ga 87Sr Organic matter
only Useful applications
To archaeology Absolute dating technique using
seasonal markings How old is Earth?
How Relative Dating i-clicker question!
formed, which layer
was deposited first? M
L A. R
E. F Principle of Superposition Principle of Superposition i-clicker question! When the rocks were originally deposited:
A. They were deposited at this angle.
B. They were deposited at a steeper
angle (closer to vertical).
C. They were deposited at a shallower
angle (closer to horizontal). Principle of original horizontality i-clicker question! When these rocks were deposited:
A. No deposition occurred where the canyon is located.
B. The rocks that make up the walls of the canyon
C. Different rocks were deposited in the canyon. Principle of Original Continuity i-clicker question!
Put the units in order from oldest to youngest:
A. T, L, O, E
B. L, T, O, E
C. T, O, E, L E
L T Principle of Cross-Cutting Relations FAULTS Principle of Cross-Cutting Relations • What happened last? The sedimentary
rocks, the dike, or the fault? Principle of inclusions Missing time… A B
Which surface is an unconformity?
C. C Unconformity in the GC Tapeats Sandstone
(~550 million years old) Vishnu Schist
(~1700 million years old) Paleozoic
Brachiopods Index Fossil- Trilobites Correlation correlation line What is missing?? Construction of a relative geologic
time scale ...
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- Fall '10
- Geology, W. W. Norton, i-clicker question, Tapeats Sandstone