1. Earth Through Time
Clues to Earth’s Past

2. Absolute Ages of Rock
1. What is absolute dating? Absolute dating is a method used to determine age, in years of rock that uses the properties of the atoms in the rock.
2. What happens during radioactive decay?
This happens when a neutron breaks down into a proton and a electron. 3. Changing the electron which leaves to beta particle (+ e). 4. While others give off a alpha particle which is two protons and two electrons (helium atom) 5. If the number of protons in an atom changes, you then change the element to a different element.

3. Half-Life
When decay occurs the parent isotope breaks down into a daughter material.
This period of time is a half-life. The time it takes half of the isotope to decay.
Examples: Carbon-14: 5,730 yrs. If daughter is formed it is Nitrogen-14. Uranium -238: 4.5 X 109 years. If daughter is formed Lead -206
Use of radioactive material for dating is also known as radiometric dating.

4. The radioactive decay curve

5. Half-life

6. Fossils 1. What can fossils tell us?
- Where, when, and how organisms lived
2. 2 most important conditions necessary for an organism to become a fossil:
1. To be buried quickly
2. Have hard parts

7. 3. How an organism’s remains petrified:
- Some or all of the original materials in the remains have been replaced by minerals.
4. How an organism’s remains can become carbonaceous film:
- The organism is buried by sediments which pile up increasing the heat and pressure. Gases and liquids are forced from body, thin film of carbon residue is left forming an outline.

8. Petrified Log

9. Trilobite

10. C. Sediments are carried into the mold and deposited.
5. Process of fossilization as an organism is buried, becomes a mold, then a cast:
A. The fossil begins to weather and erode as water moves through pores in rock layers.
B. The fossil is eroded away, the harder rock surrounding it forms a mold.
C. Sediments are carried into the mold and deposited.
D. A cast is formed.

15. 2. Trapped in amber 3. Trapped in tar
6. Three ways that the original remains are preserved:
1. Frozen in ground
2. Trapped in amber
3. Trapped in tar

24. crustacean burrows -middle Jurassic

25. coprolite (dino poo)

26. Speed animal was traveling Lifestyle of animal Social life of animal
7. Four types of information that trace fossils can tell about animals:
Size, weight, age
Speed animal was traveling
Lifestyle of animal
Social life of animal

27. 8. What do scientists use index fossils for?
- To date rock layers

28. Relative Age of Rocks What does the principle of superposition state?
In a sequence of sedimentary rock layers, the oldest layer is on the bottom, the youngest on the top.
2. How are sediments deposited?
- In horizontal layers
3. What is relative dating?
- Determining the order of events or relative ages of rocks by their position in sequence.

30. 4. What is unconformity?
- A gap in the sequence.
* Develops when sedimentary rock layers are uplifted, tilted and/or eroded away.

31. Angular Unconformity
Horizontal layers are uplifted, tilted, and eroded, then more layers are deposited horizontally.

35. Disconformity
Layers are deposited, uplifted, and eroded, more layers are deposited horizontally.

38. Nonconformity
Sedimentary layers are deposited on top of igneous or metamorphic rocks.