Geological History

2. solid copy of the shape of an organism
5. used to date fossils and rocks 60,000 years old or younger
8. drift process by which forces inside the earth cause continents to move over Earth's surface
11. break in the earth's crust
12. extinction at least 50% of the species on the earth have to have gone extinct for this to happen
13. lava that hardens on the surface of the earth
14. Bang Theory theory about the origin of the universe
15. decay process by which unstable elements breakdown by releasing particles and energy
16. record shows how particular organisms and environments have changed over time
19. lived more than 500 million years ago that are used as index fossils
21. ages happened during the Quaternary Period after Earth's climate cooled

1. rate of decay of each radioactive element
3. theory well-tested concept that explains a range of observations
4. shows where rock layers have been lost by erosion
6. when magma pushes into bodies of rock beneath the surface of the earth and hardens into igneous rocks
7. used to find the absolute ago of rocks and fossils older than 60,000 years old
9. of Superposition according to this, in horizontal sedimentary rock, each layer is younger than the layer below it
10. fossils used to find the relative age of a rock
17. first vertebrates to crawl onto land
18. fish first vertebrates
20. hollow area in sediment in the shape of an organism