Geologic Time Notes Page 3 ©Mark Place, 2007-2008 www.LearnEarthScience.com

Fossils can only be found in rocks. sedimentary

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never lived at the same time Why is this statement false: “The caveman had dinosaur for breakfast.”? man and dinosaurs never lived at the same time

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Relative Age If a sedimentary rock outcrop has not been overturned, which layer would be the oldest? What is this principle known as?

oldest rock layers are on bottom Principle of Superposition

Using this principle, label the strata below from oldest to youngest.

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Faults are always (older, younger) than the rocks they cut through.

there first (it's older) Which is older: F or S How do you know? F cuts through S S must have been there first (it's older)

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If a geologist finds an igneous sill, how can she determine if the sill is an intrusion or an extrusion?

Is “H” an intrusion or extrusion? How can you tell?

H is an intrusion. Contact metamorphism on top

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a buried erosional surface What is an unconformity? How does it complicate the relative dating of rock layers? a buried erosional surface a part of the rock record is missing

Using the diagram to the left, identify where the unconformity is located by drawing an arrow and writing the word “unconformity” next to it.

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What characteristics must fossils have in order to be good index fossils? lived over a large geographic area (large horizontal distribution) lived for a short period of time (small vertical distribution)

In geology, this is referred to as CORRELATION In the diagram below, a geologist has matched up rock layers based on index fossils.

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Evolution organisms adapt to their environment in order to survive Explain the theory of evolution. organisms adapt to their environment in order to survive

Evolution can see that different organisms have changed over time Explain how the fossil record supports this theory can see that different organisms have changed over time

their half-lives are constant Absolute Age Why are radioactive isotopes useful in determining the absolute age of a rock? their half-lives are constant

NOTHING! it is reliable to calculate age Absolute Age What can be done to change the half-life of a radioactive isotope? Why is this important? NOTHING! it is reliable to calculate age

stable atoms unstable atoms Draw the generic graph for the half-life of a radioactive isotope. stable atoms unstable atoms

carbon-14 What radioactive isotope could be Absolute Age What radioactive isotope could be used to determine the absolute age of material that was recently living? carbon-14

What is the half life of uranium-238? Please answer the two questions on page 7 of your Notes What is the half life of uranium-238? 4.5 x 109 4,500,000,000 4.5 billion years choice (c)

3 half-lives x (5.7 x 103) =1.71 x 104 = 17,100 years Please answer the two questions on page 7 of your Notes If there is a 100g sample of C14, how many grams of C14 would remain after three half-lives? How long would this take? Show all work. 100g  50g  25g  12.5g 3 half-lives x (5.7 x 103) =1.71 x 104 = 17,100 years