Presentation on theme: "“How can scientists determine the age of rocks and fossils?”"— Presentation transcript:
1 “How can scientists determine the age of rocks and fossils?” Dating“How can scientists determine the age of rocks and fossils?”
2 Geologic PrinciplesUniformitarianismThe processes occurring today have been occurring since Earth formedPresent Earth not caused by catastrophic events
3 Relative vs. Absolute Dating Relative Age DatingEstablishes the order of past geological events (ex: A is older than B)A comparison, not an exact ageAbsolute Age DatingScientists determine the numerical age of rocks and other objects (ex: Sample A is 4.6 million years old)Exact age of object
5 Relative Age Dating Original Horizontality Sedimentary rocks are deposited in (nearly) horizontal layersSuperpositionIn an undisturbed rock sequence, the oldest rocks are at the bottom and each layer above is younger than the rock layer below it
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 neutronsTo achieve stability, radioactive elements emit nuclear particles“Parent” – the original radioactive element“Daughter” – the new element
10 Absolute Age Dating Radiometric dating Half-life Process used to determine the absolute age by determining the ratio of parent nuclei to daughter nuclei in a given sampleHalf-lifeAmount of time it takes a radioactive element to decay to one half of the original amount.
11 Other Dating MethodsDendrochronologyScience of comparing annual growth rings in trees to date events and environmental changes
12 Other Dating Methods Key Beds Index Fossils Sediment layers that serve as a time marker in the rock record, result from volcanic ash or meteorite impact debrisIndex FossilsRemains of living things that are:Easily recognizedAbundantShort-lived
13 Relative DatingWhat principle states that sediments are deposited in horizontal layers?Which layer is the oldest in this rock sequence? The Youngest?What principle helped you answer questions 2?Is the fault line in this rock sequence older or younger than layer D?