Dating How can scientists determine the age of rocks and fossils?

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Dating Dating “How can scientists determine the age of rocks and fossils?”

Transcript of Dating How can scientists determine the age of rocks and fossils?

Page 1: Dating How can scientists determine the age of rocks and fossils?

DatingDating“How can scientists determine the age of rocks and fossils?”

Page 2: Dating How can scientists determine the age of rocks and fossils?

Geologic PrinciplesGeologic PrinciplesUniformitarianism

◦The processes occurring today have been occurring since Earth formed

◦Present Earth not caused by catastrophic events

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Relative vs. Absolute Relative vs. Absolute DatingDatingRelative Age Dating

◦Establishes the order of past geological events (ex: A is older than B)

◦A comparison, not an exact ageAbsolute Age Dating

◦Scientists determine the numerical age of rocks and other objects (ex: Sample A is 4.6 million years old)

◦Exact age of object

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Relative vs. Absolute Relative vs. Absolute DatingDating

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Relative Age DatingRelative Age Dating• Original Horizontality–Sedimentary rocks are deposited in (nearly) horizontal layers

• Superposition–In an undisturbed rock sequence, the oldest rocks are at the bottom and each layer above is younger than the rock layer below it

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Oldest

Youngest

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Relative Age DatingRelative Age DatingCross-Cutting relationships

◦States that an intrusion or a fault is younger than the rock it cuts across

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Absolute Age DatingAbsolute Age DatingRadioactive Decay

◦Radioactive elements have unstable nuclei due to their number of neutrons

◦To achieve stability, radioactive elements emit nuclear particles

◦“Parent” – the original radioactive element

◦“Daughter” – the new element

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Absolute Age DatingAbsolute Age DatingRadiometric dating

◦ Process used to determine the absolute age by determining the ratio of parent nuclei to daughter nuclei in a given sample

Half-life◦ Amount of time it takes a radioactive

element to decay to one half of the original amount.

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Other Dating MethodsOther Dating MethodsDendrochronology

◦Science of comparing annual growth rings in trees to date events and environmental changes

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Other Dating MethodsOther Dating MethodsKey Beds

◦Sediment layers that serve as a time marker in the rock record, result from volcanic ash or meteorite impact debris

Index Fossils◦Remains of living things that are: Easily recognized Abundant Short-lived

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Relative DatingRelative Dating1. What principle states that

sediments are deposited in horizontal layers?

2. Which layer is the oldest in this rock sequence? The Youngest?

3. What principle helped you answer questions 2?

4. Is the fault line in this rock sequence older or younger than layer D?