The Rock Record

Chapter 8

Preview the chapter pages 184-201

• Look at headings

• Look at pictures

• Read the yellow highlighted words

Assignment

• Read your assigned section.

• Take notes on the section

• Think of a clever way for you and the other students to remember the information in your section.

• Prepare to go in front of the class and teach your section.

• Write a simple statement of what your section covered on the board.

• You may use pictures, diagrams or act it out!

Sections• 1. Determining relative age 185• 2. Uniformatarianism 185• 3. Earth’s age 186• 4. Relative age 186• 5. Law of superposition 187• 6. Principle of original Horizontality 187• 7. Graded bedding 188• 8. Cross-beds 188• 9. Ripple marks 188• 10. Unconformities 189• 11. Types of unconformities chart 189• 12. crosscutting relationships 190• 13. Determining absolute age/absolute dating methods intro 191• 14. Rates of erosion 191• 15. Rates of deposition 192• 16. Varve count 192• 17. Radiometric dating 193• 18. Radioactive decay of uranium 193• 19. Half-life 194• 20. Radioactive isotopes 195• 21. Carbon dating 196• 22. The fossil record 197• 23. Interpreting the fossil record 197• 24. Fossilization 198• 25. Table 1 page 198 198• 26. Table 2 page 199 199• 27. Types of Fossils 199• 28. Index fossils 200• 29. Index fossils and absolute age 200

1. Determining relative age 185

• 1. How old do geologists’ estimate the earth to be?

4.6 billion years

Uniformatarianism 185

• 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!

Earth’s age 186

• 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

Relative age 186

• 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.

Law of superposition 187

• 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.

Principle of original Horizontality187

• 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.

Layers that are not horizontal • Had an external force that moved then…

Graded bedding 188

• 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.

Cross-beds 188

• What type of sediment forms cross beds?

• Sandy sediment forms cross beds because the tops of the layers often erodes away before the next layer is deposited.

Ripple marks 188

• What causes ripple marks?

• Water or wind

Unconformities 189

• What is an unconformity?

• Break in the geologic record due to erosion or no sediment being deposited.

Types of unconformities chart 189

• List the three types of unconformities.

• Non conformity

• Angular unconformity

• Disconformity

crosscutting relationships 190

• What is a fault?

• Which is older? The fault material or the original rock?

• A break or crack in the earth’s crust along with a shift in rock position.

• The fault is younger then the rock through which it breaks.

• Sequence the rock layers and geologic events that must have taken place to produce the cross section. For each event, list the principle that you used to determine it's place in the sequence. Then click ahead to see how you did.

• Notice that there is a folded sequence of rocks beneath the flat-lying layers. If we straighten these folded layers, the oldest rock is the Tecate Arkose.

The Berry Breccia is next oldest by the Principle of Superposition.

• Then comes in order the Apple Sandstone, the Kiwi Shale, and the Coal all by the Principle of Superposition.

• These rocks were then folded prior to the deposition of the Banana Sandstone. We know this by the Principle of Original Horizontality

• After the folding, the Banana Sandstone was deposited in order by the Tequila Shale and the Mezcal Limestone by the Principle of Superposition.

• Finally, Deadman's Canyon is the youngest geologic feature. We know this by the Principle of Lateral Continuity. The rocks on the cliff with the stickperson are the same as the rocks on the other cliff. Therefore the canyon must be younger than those rocks.

Determining absolute age/absolute dating methods intro 191

• What does absolute age mean?

• Numeric age; exactly how old in years something is.

Rates of erosion 191

• How can rate of erosion be used to get the absolute age of something?

• When is it most accurate?

• 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.

• Best used for things under 20,000 years old.

Rates of deposition 192

• What is deposition?

• What is a rate?

• Is the rate always constant?

• Deposition is placement of Sediments over time.

• Rate is amount deposited over time.

• Rate is not always constant.

Varve count 192

• What is a varve?

• How are they like rings of growth in trees?

• 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.

• Like tree rings they show annual “growth” and can be counted to determine the age of the structure.

Radiometric dating 193

• What do radioactive isotopes release?

• What happens to the atom as it releases energy?

• How is absolute age determined?

• They release energy at a constant rate.

• The atom changes into a different isotope as it releases energy.

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

Radioactive decay of uranium 193

• Uranium 238 emits 2 protons and 2 neutrons in a process called ___________.

• When does the radioactive isotope stop changing?

• Alpha decay

• It continues until a stable non-radioactive form of lead is formed.

Half-life 194

• What is half life?

• The time it takes for ½ of a radioactive element to decay back to its daughter isotope.

Radioactive isotopes 195

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

Radioactive isotopes 195

• 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.

Carbon dating 196• Carbon dating uses ___________material in

rock that is less then ____________years old.

• How is the age determined?

• Living things have more carbon _______.

• dead things have_____________.

• ( the isotope carbon 14 becomes after many years)

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 fossil record 197

• Why is the study of paleontology important to learning about the past events on the earth?

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.

Interpreting the fossil record 197

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

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.

Fossilization 198

• Why do most plants and animals not leave fossils?

Fossilization 198

• Why do most plants and animals not leave fossils?

• The remains are usually broken down by bacteria.

25. Table 1 page 198 198

• List 4 ways fossils may be produced.

25. Table 1 page 198 198

• List 4 ways fossils may be produced.

• Mummification

• Amber

• Freezing

• petrification

26. Table 2 page 199 199

• What is left behind to form imprints?

• What is fossilized waste material called?

26. Table 2 page 199 199

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

• What is fossilized waste material called?– coprolites

27. Types of Fossils 199

• What type of fossil leaves behind evidence of movement or activity of a living organism?

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 ________________fossils.

28. Index fossils 200

• If a fossil only appears in rocks of a certain age they are called ____index________fossils.

29. Index fossils and absolute age200

• Index fossils usually live for relatively __________periods of geologic time. This helps paleontologists estimate the age of the rock in which they are found more________________.

• ___________________are also often used to find oil or natural gas deposits.

29. Index fossils and absolute age200

• 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 are also often used to find oil or natural gas deposits.

Chapter 8 Highlights page 201

• Review questions page 202

• 8-14

• 16, 18, 20, 21

• 29 and 30

• 33-35

• UNIFORMATARINISM

The Law of Uniformity, or the Principle of Uniformitarianism, states that in interpreting past events in geologic history, they should be explained in terms of presently observable processes and phenomena.

Law of Uniformity

• The present is the key to the past!

• James Hutton changed the way geologist’s believed Earth’s formations were formed.

Law of superpositionTop layers are youngest,

bottom layers are the oldest