dating rocks ways to tell the age of a rock. 2 ways to date rocks: relative dating: places events...
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Dating RocksDating Rocks
Ways to tell the age of a rock
Ways to tell the age of a rock
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2 Ways to Date Rocks:2 Ways to Date Rocks:
Relative Dating: Places events in geologic history in the
proper order. The basis for the geologic time scale Mainly Sedimentary Rocks Does not provide a true “age”
Relative Dating: Places events in geologic history in the
proper order. The basis for the geologic time scale Mainly Sedimentary Rocks Does not provide a true “age”
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2 Ways to Date Rocks:2 Ways to Date Rocks:
Absolute Dating: All you need is a tiny sample of material
(mineral, bone) no larger than a grain of rice. Gives us the true “age” of a fossil or rock Mainly organic tissue or igneous crystals Measure the amount of unstable isotopes that
have “decayed” to figure out age Radiometric dating
Absolute Dating: All you need is a tiny sample of material
(mineral, bone) no larger than a grain of rice. Gives us the true “age” of a fossil or rock Mainly organic tissue or igneous crystals Measure the amount of unstable isotopes that
have “decayed” to figure out age Radiometric dating
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Principles for Relative Dating:
• Superposition - The youngest rocks are on the top, oldest at the bottom.
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Relative Dating Principles• Superposition • Cross-cutting relationships - Geologic
features that cut through and across rocks are younger than those rocks.
• Mostly Faults and Igneous intrusions
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Cross-cutting Igneous Rock
Cross Cutting Relationships - Geologic features that cut through and across rocks are younger than those rocks.
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Relative Dating Principles• Superposition• Cross-cutting relationships• Law of Inclusions - Rocks embedded in
other rocks are older than those rocks they are embedded in.
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http://www.earth.ox.ac.uk/~oesis/field/medium/xenolith-1365.jpg
Law of Inclusions - Rocks embedded in other rocks are older than those rocks they are embedded in.
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Relative Dating Principles• Superposition• Cross-cutting relationships• Law of Inclusions• Law of Original Horizontality (and
Lateral continuity) – layers of sediments are originally deposited horizontally
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Hikingtripsreport.com
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Relative Dating Principles• Superposition• Cross-cutting relationships• Law of Inclusions• Law of Original Horizontality (and
Lateral continuity)• Law of Unconformities
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A DISCONFORMITY is a boundary between two layers of non-continuous ages. This boundary is usually marked by an erosional surface and is often irregular.
M&W4 Fig. 17.8; M&W5 Fig. 17.8
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An ANGULAR UNCONFORMITY is a disconformity between layers of different angles.
The underlying layers are first tilted, then erosion scours away a new, horizontal surface.
New, horizontal layers form on top
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An NONCONFORMITY is a disconformity between different rock types, one of them sedimentary.
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Activity 2: Label the layers from:
A The Oldest
T The Youngest
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Activity 2: Label the layers from:
A The Oldest
T The Youngest
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Name:___________________ Core: 1 2 3 4
What are two ways to date rocks?
1._________________________
2._________________________