Geologic Time Geologic Time Notes

Fossils can only be found in rocks. SEDIMENTARY

Why is this statement false? “The cavemen ate dinosaur for breakfast.” Man and dinosaurs did not live at the same time. 65 million years apart

Name the primary way that geologists find the absolute and relative age of rock layers. ABSOLUTE AGE Radioactive dating RELATIVE AGE Ordering rock layers

Use your Earth Science Reference Tables Pages 3, 8 & 9; Maybe 6 & 7 Answers Questions Use your Earth Science Reference Tables Pages 3, 8 & 9; Maybe 6 & 7

Answers the Questions 1 Approximately how many million years ago did the earliest amphibians appear? 359-416 2 Approximately how many million years ago was the initial opening of the Atlantic Ocean? 146-200 3 During which era did the earliest fish appear? Paleozoic 4 During which epoch did large carnivores appear? Pliocene 5 Of the following rocks which would be most likely to contain fossils? a. rhyolite b. basalt c. metaconglomerate d. limestone limestone (it’s sedimentary) 6 At Binghamton, NY what is age of the bedrock? Devonian (359-416million years) 7 How does the age of the bedrock at Old Forge compare with that at Jamestown? Jamestown is younger 8 Name a location in NY State where you may be able to find bedrock which was formed at the peak of the eurypterid’s development. Silurian age bedrock: Niagara Falls, Syracuse 9 Why would fossils be unlikely to be found in quartzite? it’s metamorphic 10 For each of the following locations in NY State below, identify whether fossils would be likely or unlikely: Old Forge; Binghamton; Albany Old Forge: unlikely Binghamton: likely Albany: likely

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The age of an object compared to other objects. Relative Age The age of an object compared to other objects. Saying one object is older than another. Related (relative) means compared to. Fossils, rock layers, history

The actual age of an object expressed in time. Absolute Age How old something really is. The actual age of an object expressed in time. Absolutely means “fer sure.” Fossils; history

Principle of Uniformitarianism I thought of it. Things that happen today probably happened in the past. Copy-cat! James Hutton I know you are but what am I? But I made it popular. “The present is the key to the past.” Charles Lyell

Oldest rock layers are on the bottom. Relative Age If a sedimentary rock outcrop has not been overturned, which layer would be the oldest? Oldest rock layers are on the bottom.

Principle of Superposition What is this principle (oldest on bottom) known as? Principle of Superposition

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

On to the next question...

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) Not in your notes!

Which is older: rock layer 7 or fault ? Why? Rock layer 7 is cut by the fault.

Which is older: rock layer 12 or fault ? Why? Rock layer 12 is NOT cut by the fault.

On to the next question...

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

Intrusions contact metamorphism on all sides

no contact metamorphism extrusions no contact metamorphism on top

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

H is an intrusion. Contact metamorphism on top

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

weathering and erosion What processes could lead to an unconformity? weathering and erosion

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 wide geographic distribution (lots of places). Horizontally abundant Short-lived (became extinct quickly). Vertically limited

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

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 Different organisms have changed over time. Explain how the fossil record supports this theory Different organisms have changed over time. 99.9% of all living things are extinct.

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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

Trials Students

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 5,700 yr 11,400 yr 17,100 yr 3 half-lives x (5.7 x 103) =1.71 x 104 = 17,100 years