| A | B |
|---|
| Age of the Earth | 4.6 billion years old (4.6 x10^9) |
| Law of Superposition | Oldest rocks are at the bottom, newest are at the top |
| Law of Crosscutting Relationships | An igneous intrusion, fault, or other formation is younger than the rock it cuts through. |
| Law of Original Horizontality | Sedimentary rock will deposit in horizontal layers |
| Law of Lateral Continuity | Rocks will spread out laterally. If a piece of rock is missing, we can use this law to figure out what was once there. |
| half life | how long it takes for half a radioactive element to decay. |
| Carbon -14 half life | 5,700 years |
| Uranium 238 half life | 4.4 billion years |
| When to use Carbon-14 | Use on a once living thing, can't be too old (run out of Carbon 14) |
| When to use Uranium 238 | Use on non living objects, can date very old rocks |
| Relative vs absolute age | Relative age is a comparison, absolute age is a number |
| uniformitarianism | Assumption of what happens in the present also happened in the past. Can use to understand what processes affected the Earth a long time ago. |
| Radioactive material X has a half life of 10,000 years. If a sample of 20 g was found, how much will be left after 40,000 years. | 1.25 grams |
| A rock with 25 grams of radioactive material and 75 grams of stable material was found in a rock. If the half life is 500 years, how old is the rock? | 1,000 years old |
