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Geology. 1. Determining relative age 185 1. How old do geologists’ estimate the earth to be? 4.6 billion years. James Hutton. 2. Uniformatarianism 185
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1. Determining relative age 185 • 1. How old do geologists’ estimate the earth to be? 4.6 billion years
2. Uniformatarianism 185 • 2. What does the principle of Uniformatarianism tell us? Current geologic processes, like erosion, also occurred in the past. The present is the key to the past!
3. Earth’s age 186 • 3. Why did Hutton believe the earth to be older then the 6,000 year estimate first proposed by scientists? • The earth must be very old for slow processes like erosion to have created complex rock structures
4. Relative age 186 • 4. What is relative age?Relative age tell which rock layer is older then the other but does not tell the exact age in number of years.
5. Law of superposition 187 • 5. What does the law of superposition tell us?Superposition tells us that the oldest layers of rock are on the bottom because they were deposited first and the youngest are on the top because they were deposited most recently.
6. Principle of original Horizontality187 • 6. What does this principle tell us about the rock layers?Original horizontality tells us that when rock layers are put down they form horizontal beds and unless something disturbs them they will stay that way.
7. Graded bedding 188 • 7. Where are the coarse particles found in a graded bed?_ • Graded bedding means that coarse layers are found on the bottom because they are heavier. They will remain there unless something causes them to be overturned.
8. Cross-beds 188 • 8. What type of sediment forms cross beds?Sandy sediment forms cross beds because the tops of the layers often erode away before the next layer is deposited.
9. Ripple marks 188 • 9. What causes ripple marks? Water or wind
10. Unconformities 189 • 10. What is an unconformity? • Break in the geologic record due to erosion or no sediment being deposited.
11. Types of unconformities chart 189 • 11. List the three types of unconformities. • non conformity • Angular unconformity • Disconformity
12. Crosscutting relationships 190 • 12. What is a fault? ___ • A break or crack in the earth’s crust along with a shift in rock position.
12. Which is older? The fault material or the original rock? The fault is younger then the rock through which it breaks
an idea that was first proposed by James Hutton in the 18th century. • State the principle of uniformitarianism. uniformitarianism a principle that geologic processes that occurred in the past can be explained by current geologic processes
Explain how the law of superposition can be used to determine the relative age of rocks.
Chapter 8 Law of Superposition The diagram below illustrates the law of Superposition.
Apply the law of crosscutting relationships to determine the relative age of rocks.
relative age the age of an object in relation to the ages of other objects • Layers of rock, called strata, show the sequence of events that took place in the past. • Relative age indicated that one layer is older or younger than another layer but does not indicate the rock’s age in years.
law of superposition the law that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed
Scientist know that sedimentary rock generally forms in horizontal layers.
unconformity a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time
Which layer is the oldest? How do you know? Is the igneous intrusion older or younger then the rocks it cuts across? What principle is used to answer this question?
Complete the problem solving lab on page 560 of the Glencoe book. • Write the answers 1-6 on your paper.
Problem solving Lab • 1. Layer B • 2. Between D And F Between E and F • 3. Changes by contact metamorphism. • 4. A fault occurred/ a break along which movement occurred caused misalignment • 5. The dike is younger according to the cross cutting relationship principle. • 6. b,c,d, e superposition • A intrusion cross cutting relationship • Folding of layers ABCD • D eroded • FGHI deposited superposition / horizontality • Faulting: principle of crosscutting relationship
Section 2 • 13. Determining absolute age/absolute dating methods intro 191 • 13. What does absolute age mean? _Numeric age; exactly how old in years something is.
14. Rates of erosion 191 • 14. How can rate of erosion be used to get the absolute age of something? • By seeing how much erosion happens in one year it can be estimated how old something is by measuring the amount of erosion per year.
14. When is it most accurate? Best used for things under 20,000 years old. Niagara Falls moves 1.2 meters a year! Due to erosion it has moved 11 kilometers since the Ice Age, when it was formed
15. Rates of deposition 192 • 15. What is deposition? • Deposition is placement of Sediments over time.
15. What is a rate? • Rate is amount deposited over time Amount time
15. Is the rate always constant? • Rate is not always constant
16. Varve count 192 • 16. What is a varve? __A varve is a layer in sedimentary rock that shows sand and silt that are deposited based on the season. • They have light and dark sections. • How are they like rings of growth in trees? Like tree rings they show annual “growth” and can be counted to determine the age of the structure.
They have light and dark sections. How are they like rings of growth in trees? Like tree rings they show annual “growth” and can be counted to determine the age of the structure.
radiometric dating a method of determining the absolutes age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.
