Science

7. age the age of rock given as the number of years since the rock formed
8. age the age of a rock compared to the ages of other rocks
9. change over time
11. a gap in the geologic record that shows where rock layers have been lost due to erosion
14. a break in earth's crust
16. decay the process in which the nuclei of radioactive elements break down releasing fast moving particles and energy
17. a fossil that is a solid copy of an organism's shape formed when minerals seep into a mold
18. a group of organisms that has died out and has no other members living

1. an igneous rock layer formed when lave flows onto earth's surface and hardens
2. fossil a type of fossil that provides evidence of the activities of ancient organisms
3. The preserved remains or traces of an organism that lived in the past
4. a scientist who studies fossils to learn about organisms that lived long ago
5. fossil fossils of widely distributed organisms that lived during a geologically short period
6. fossil a fossil in which minerals replace all or part of an organism
10. a type of fossil that is a hollow area in sediment in the shape of an organism
12. an igneous rock layer formed when magma hardens beneath earth's surface
13. of superposition a basic law of geochronology, stating that in any undisturbed sequence of rocks and deposited in layers, the youngest layer is on top and the oldest on bottom, each layer being younger than the one beneath it and older than the one above it
15. the time it takes for half of the atoms of radioactive elements to decay
19. film a type of fossil consisting of an extremely thin coating of carbon on rock