Geological History

2. break in the earth's crust
4. used to find the relative age of a rock
5. according to this, in horizontal sedimentary rock, each layer is younger than the layer below it
6. process by which unstable elements breakdown by releasing particles and energy
9. shows where rock layers have been lost by erosion
10. rate of decay of each radioactive element
14. first vertebrates to crawl onto land
17. process by which forces inside the earth cause continents to move over Earth's surface
18. happened during the Quaternary Period after Earth's climate cooled
19. well-tested concept that explains a range of observations
21. hollow area in sediment in the shape of an organism

1. lava that hardens on the surface of the earth
3. lived more than 500 million years ago that are used as index fossils
7. used to date fossils and rocks 60,000 years old or younger
8. used to find the absolute ago of rocks and fossils older than 60,000 years old
11. shows how particular organisms and environments have changed over time
12. theory about the origin of the universe
13. at least 50% of the species on the earth have to have gone extinct for this to happen
15. solid copy of the shape of an organism
16. first vertebrates
20. when magma pushes into bodies of rock beneath the surface of the earth and hardens into igneous rocks