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

• 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

Ripples and mud cracks

• 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

Angular unconformity

• 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

• State the principle of uniformitarianism.

uniformitarianism a principle that geologic processes that occurred in the past can be explained by current geologic processes

•an idea that was first proposed by James Hutton in the 18th century.

• Explain how the law of superposition can be used to determine the relative age of rocks.

Chapter 8Law of Superposition

The diagram below illustrates the law of Superposition.

• Compare three types of unconformities.

• 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.

• 17. Radiometric dating 193

• 17. What do radioactive isotopes release? They release energy at a constant rate.

• 17. What happens to the atom as it releases energy? The atom changes into a different isotope as it releases energy.

• 17. How is absolute age determined?

• By comparing how much of the original isotope is present and how much has changed, they can determine the absolute age of the rock

• 18. Radioactive decay of uranium 193

• 18. Uranium 238 emits 2 protons and 2 neutrons in a process called __ Alpha decay

• 18. When does the radioactive isotope stop changing? It continues until a stable non-radioactive form of lead is formed.

• Scientists use the natural breakdown of isotopes to accurately measure the absolute age of rock, which is called radiometric dating.

• To do this, scientists measure the concentration of the parent isotope or original isotope, and of the newly formed daughter isotopes. Then, using the known decay rate, they can determine the absolute age of the rock.

• 19. Half-life 194

• 19. What is half life? ___ The time it takes for ½ of a radioactive element to decay back to its daughter isotope.

• 20. Radioactive isotopes 195

• 20. Why is a different isotope needed depending on the age of the rock being dated?

• The isotopes decay at different rates (the half lives are different) so the rate must match the approx age of the rock being tested.

• 21. Carbon dating 196

• Carbon dating uses organic material in rock that is less then 70,000 years old.

• The ratio of carbon 14 to carbon 12 is determined.

• Living things have more carbon 14. Dead things have nitrogen 14.

• ( the isotope carbon 14 becomes after many years

• (The isotope carbon 14 becomes after many years)

• 21. Carbon dating 196• Carbon dating uses organic material in

rock that is less then 70,000 years old.• The ratio of carbon 14 to carbon 12 is

determined. • Living things have more carbon 14.

Dead things have nitrogen 14. ( the isotope carbon 14 becomes after many years

• (The isotope carbon 14 becomes after many years)

Chapter 8Objectives

• Describe four ways in which entire organisms can be preserved as fossils.

• List five examples of fossilized traces of organisms.

• Describe how index fossils can be used to determine the age of rocks.

fossils the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock

paleontology the scientific study of fossils

• Fossils are an important source of information for finding the relative and absolute ages of rocks.

• Fossils also provide clues to past geologic events, climates, and the evolution of living things over time.

• Section 3 the fossil record

• 22. The fossil record 197

• Why is the study of paleontology important to learning about the past events on the earth? Plant and animal remains give clues of past climate, geologic events and the types of living things at that time.

• 23. Interpreting the fossil record 197

• What does it mean if fossils of marine animals are found far from a current ocean?

• The area may have once been under water years ago.

• 24. Fossilization 198

• Why do most plants and animals not leave fossils? The remains are usually broken down by bacteria.

• 25. Table 1 page 198

• List 4 ways fossils may be produced Mummification, Amber, Freezing ,petrification

• 26. Table 2 page 199

• What is left behind to form imprints? A carbon rich film

• What is fossilized waste material called? _ coprolites

• 26. Table 2 page 199

• What is left behind to form imprints? A carbon rich film

• What is fossilized waste material called? _ coprolites

• Almost all fossils are discovered in sedimentary rock.

• The fossil record provides information about the geologic history of Earth.

• Scientists can use this information to learn about how environmental changes have affected living organisms.

• 27. Types of Fossils 199• What type of fossil leaves behind evidence of

movement or activity of a living organism?– Trace fossils

• 28. Index fossils 200• If a fossil only appears in rocks of a certain

age they are called index fossils.• Index fossils and absolute age 200• 29. Index fossils usually live for relatively

short periods of geologic time. This helps paleontologists estimate the age of the rock in which they are found more accurately.

Index fossils

Review questions

• Chapter 8

• #8-14,16,18,20, 21,29,30,33-35

• Chapter 9

• # 8,9,10,14,15,17,22,31,32

Chapter 8

• #8,10,11,12,13,14,16,18,19,20,29,33,35

Chapter 9

Extended responsepage 204 #6

Part Acontrast the nodules found in modern-day Illinois with more common ones

• Usually nodules contain only hard parts like bones, shells and teeth

• Illinois nodules are unusual because they contain both soft and hard parts

Part B: What might scientists hope to learn…

• Soft parts might have muscle impressions or organ impressions

• This might tell us more about internal structures or body systems of ancient organisms.

• Scientists can compare structures to present day organisms to see change over time.

Page 230 #5

• Precambrian time ended about 542 million years ago. One reason that fossils in Precambrian rock are rare is that Precambrian organisms did not have hard body parts that commonly form fossils.

• What geophysical reasons account for the rarity of fossils in rocks of Precambrian time?

Answers should include

• Volcanic activity • Erosion• Crustal movement• all destroy fossils that did exist • Precambrian time was 542 Million years

ago so the fossils have been exposed to geophysical events for a very long time

• Much longer then the more recent time periods like Cenozoic and Mesozoic etc.

Interpreting GraphicsUse the figure below to answer question 11.

The graph shows the rate of radioactive decay.

Interpreting Graphics,

11. How many half-lives have passed when the number of daughter atoms is approximately three times the number of parent atoms?

A. one

B. two

C. three

D. four a waning moon.