Relative Time. Relative Dating Relative dating – events are placed in a sequence, but actual...
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Transcript of Relative Time. Relative Dating Relative dating – events are placed in a sequence, but actual...
![Page 1: Relative Time. Relative Dating Relative dating – events are placed in a sequence, but actual occurance dates are unknown. Who is older, Mr. Kopp or Justin.](https://reader035.fdocuments.us/reader035/viewer/2022062318/551773015503463e368b4d0e/html5/thumbnails/1.jpg)
Relative Time
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Relative Dating
• Relative dating – events are placed in a sequence, but actual occurance dates are unknown.
• Who is older, Mr. Kopp or Justin Bieber?
• What are our actual ages? – Absolute Dating
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Relative Dating Geologic Laws
• Principle of Uniformitarianism – idea that the same geologic processes that are occuring today ALSO occurred in the past
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Law of Original Horizontality
• SEDIMENT IS DEPOSITED HORIZONTALLY
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Law of Superposition
• If sedimentary rocks are undisturbed – THE OLDEST LAYERS ARE ON THE BOTTOM and YOUNGER LAYERS ARE ON TOP
B
A
C
D
oldest
youngest
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Law of Crosscutting
• A cutting feature is younger than the layers it cuts through
A
B
C
D
E
oldest
youngest
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Law of Included Fragments
• Pieces of rocks are older than the layers of rock in which they are found
e ee
B
D
C
A
oldest
youngest
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“Unconformity Rule”• A place in the rock record where layers of rock are missing and gaps in
geologic time exist. The layers were deposited and worn away OR never existed. The result is a large difference between rocks above and below the eroded surfaces.
C
B
A
D
E
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Law of Faunal Succession
• Older rocks contain the remains of older and more simple creatures and younger rocks contain younger more complex creatures
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Absolute Time
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Radiometric Dating
• Calculation of the exact age of rocks using radioactive isotopes
Remember Relative Dating is only a comparison of the ages of rock layers (older or younger)
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How Does Radiometric Dating Work?
• Atomic # = ?
• Atomic Mass # = ?
• Isotope – an element with the same number of protons but a DIFFERENT NUMBER OF NEUTRONS = unstable nucleus
• Radioactivity: when nuclei are unstable (radioactive isotopes), they spontaneously break apart or decay
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How Does Absolute Dating Work?
• PARENT = radioactive isotope which decays into a stable DAUGHTER product.
• Radioactive decay continues until a stable daughter product is formed….which happens within a predictable time period known as a half-life.
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How does Relative Dating Work?
• Half-life – rate of radioactive decay (the amount of time it takes for HALF of the nuclei of a radioactive isotope to decay into its stable daughter product)
• Uranium-238 decays into Lead-206 (4.5 by)• Uranium-235 decays into Lead-207 (713 my)• Thorium-232 decays into Lead-208 (14.1 by)• Rubidium-87 decays into Strontium-87 (47 by)• Potassium-40 decays into Argon-40 (1.3 by)
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How does absolute dating work?
• Each radioactive isotope has been decaying at a constant rate since the formation of the rocks in which it occurs.
• Question?• Why have the oldest rocks on Earth been
dated at 3.9 billion years old yet the Earth has been determined to be 4.6 billion years old?
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Carbon-14
• Radiocarbon dating – all organisms contain carbon-14 allowing scientists to determine the age of recent fossils
• Carbon -14 has a half life of 5,730 and can help scientists date recent geologic events up to 75,000 years ago making it extremely valuable for human history
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Index Fossils
• Used to define and identify geologic periods• Widespread, existed in a specific period of
time
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Geologic Time Scale
(Divided based upon major geologic and evolutionary events)
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Eons
• Largest divisions of geologic time
1) Pre-Cambrian 4.6 billion – 540 million years ago - Largest period of time 7/8 of the Earth’s History- Formation of the Earth, rise of life (3.7 bya), to the
first invertebrates
2) Phanerozoic (540 million years ago to present day)- Complex life on Earth
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Eras
• 2nd Largest divisions of geologic time
1) Pre-Cambrian – rise of early life2) Paleozoic – rise of complex life3) Mesozoic – age of the dinosaurs4) Cenozoic – age of mammals
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Periods and Epochs
• Pre-Cambrian 4.6 billion years ago to 540 million years ago (life appears 3.7 bya)
• Earth Formed, Moon Formed, Heavy Bombardment
• Bacteria• Stromatolites (blue-green algae)
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Periods and Epochs
• Phanerozoic Eon, Paleozoic Era• Cambrian Period 540 to 490 mya• Most major animal groups appear• Arthropods and mullosks
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Periods and Epochs
• Phanerozoic Eon - Paleozoic Era• Ordovician Period – 490 to 443 mya• Massive Marine LifeDiversification
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Periods and Epochs
• Phanerozoic Eon, Paleozoic Era• Silurian Period – 443 to 417 million years ago• Life comes on land
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Periods and Epochs
• Phanerozoic Eon, Paleozoic Era• Devonian Period – 417 to 354 million years
ago• Age of fishes
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Periods and Epochs
• Phanerozoic Eon, Paleozoic Era• Carboniferous Period• Mississippian and Pennsylvanian Epoch – 354 to 290 million
years ago• Age of plants
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Periods and Epochs
• Phanerozoic Eon• Paleozoic Era• Permian Period – 290 to 248 million years ago
• MASS EXTINCTION of 90% of species
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Periods and Epochs
• Phanerozoic Eon, Mesozoic Era• Triassic Period – 248 to 206 million years ago• Rise of reptiles
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Periods and Epochs
• Phanerozoic Eon, Mesozoic Era• Jurassic Period – 206 to 144 million years ago• Dinosaurs rules the land
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Periods and Epochs
• Phanerozoic Eon, Mesozoic Era• Cretaceous Period – 144 to 65 million years
ago• Rise of Flowering plants – End of Dinosaurs
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Periods and Epochs
• Phanerozoic Eon, Cenozoic Era• Tertiary Period • Paleocene Epoch - 65 to 54.8 million years ago• Age of Mammals
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Periods and Epochs
• Phanerozoic Eon• Cenozoic Era• Quarternary Period • Pleistocene Epoch - 1.8 to million years ago to
10,000 years ago
• Modern organisms – RISE OF HUMANS
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Periods and Epochs
• Phanerozoic Eon• Cenozoic Era• Quarternary Period • Holocene Epoch - 10,000 years ago to present