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

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Presentation on theme: "Dating How can scientists determine the age of rocks and fossils?"— Presentation transcript:

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

2 Geologic Principles Uniformitarianism The processes occurring today have been occurring since Earth formed Present Earth not caused by catastrophic events

3 Relative vs. Absolute Dating Relative Age Dating Establishes the order of past geological events (ex: A is older than B) A comparison, not an exact age Absolute 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

4 Relative vs. Absolute Dating

5 Relative 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

6 Oldest Youngest

7 Relative Age Dating Cross-Cutting relationships States that an intrusion or a fault is younger than the rock it cuts across

8 Absolute Age Dating Radioactive 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


10 Absolute Age Dating Radiometric 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.

11 Other Dating Methods Dendrochronology Science of comparing annual growth rings in trees to date events and environmental changes

12 Other Dating Methods Key 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

13 Relative Dating 1. 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?

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