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Relative Dating Study Guide

Relative dating is used to determine the age of rocks and fossils in comparison to one another, rather than assigning an absolute age in years. There are several principles of relative dating: 1) the law of superposition states that younger sedimentary layers are deposited on top of older layers, 2) the law of original horizontality states that sedimentary layers are deposited horizontally and any tilting occurred later, and 3) the law of cross-cutting relationships states that any intrusions or faults that cut through existing rocks must have occurred after the existing rocks formed. Correlation allows matching of rock layers between different locations using matching fossils. Unconformities represent gaps in the geologic record due to periods of erosion. Index fossils like tril

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57 views2 pages

Relative Dating Study Guide

Relative dating is used to determine the age of rocks and fossils in comparison to one another, rather than assigning an absolute age in years. There are several principles of relative dating: 1) the law of superposition states that younger sedimentary layers are deposited on top of older layers, 2) the law of original horizontality states that sedimentary layers are deposited horizontally and any tilting occurred later, and 3) the law of cross-cutting relationships states that any intrusions or faults that cut through existing rocks must have occurred after the existing rocks formed. Correlation allows matching of rock layers between different locations using matching fossils. Unconformities represent gaps in the geologic record due to periods of erosion. Index fossils like tril

Uploaded by

Eric Rivers
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© © All Rights Reserved
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Notes: Relative Dating Name ___________________

Eric
Relative Dating is when you give the age of a rock or fossil compared to another rock or fossil.
I. _______________________

– Example: Rock A is OLDER than Rock B.


– An actual age in years is not determined.

II. Rules of Relative Dating


1. Law of superposition When sedimentary rock layers are deposited, younger layers
___________________________:
are on top of older deposits.

2.Law of original horizontality Sedimentary rock layers are deposited horizontally.


________________________________:
If they are tilted, folded, or broken, it happened later.

Law of cross cutting relationships


3. _____________________________________: If an igneous intrusion or a fault cuts through
Younger
existing rocks, the intrusion/fault is _______________________ than the rock it cuts through

Correlation
III. ____________________________________: Rock layers in different places and be correlated or
matched up by matching up the rocks and fossils in the layers.
Unconformity
IV. _________________________________: When rock has been eroded, so you have a missing section
of time in the rock record.

Index fossils
V. _____________________________________: Some species of organisms only lived for a short period of
time before they became extinct. If you use radiometric dating to get an age for the fossil, then you know that
the rock the fossil is found in is also that age.

Trilobite: Graptolite:
Palezoic Era
Index fossil of the _____________________ Ordovican
Index fossil of the Period
_____________________
590-250
Age: ___________________________MYA 500-335
Age: ___________________________MYA

Faulting U than Erosian R


___________________________________ Folding L then Erosion R
_______________________________________

___________________________________ _______________________________________

___________________________________ _______________________________________

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