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Relative Dating of Rocks Layers. Age of Earth. Early 1900s: 6000 years old Today: 4.6 billion years old How did scientist come up with this number? Relative Age Dating Absolute Age Dating. James Hutton (1700s) Developed the principle of uniformitarianism
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Age of Earth • Early 1900s: 6000 years old • Today: 4.6 billion years old How did scientist come up with this number? • Relative Age Dating • Absolute Age Dating
James Hutton (1700s) • Developed the principle of uniformitarianism • processes occurring today have been occurring since Earth formed.
1) Relative Age Dating • Comparing one rock layer to another. • Sequences the order of events • No exact dates • Easy comparison of fossil ages
Geologic Principles • Original Horizontality – sedimentary rocks are deposited in horizontal layers.
Superposition– in an undisturbed rock sequence: • Oldest rock layers are at the bottom • Youngest layers are on top
Law of Superposition • Which layer is the oldest? • Which layer is the youngest? • Would the fossils in rock layer “U” be older or younger the fossils in rock layer “X”? • How do you know? L U M X S