Geologic Time

3. Type of fossil consisting of an extremely thin coating of carbon on rock
4. Igneous rock layer formed when lava flows onto Earth's surface and hardens
8. Record of the geologic events and life forms in Earth's history
10. A type of fossil that provides evidence of the activities of ancient organisms
13. A loose collection of ice and dust that orbits the sun, typically in a long narrow orbit
15. A gap in the geologic record that shows where rock layers have been lost due to erosion
16. The preserved remains or traces of an organism that lived in the past
17. Fossils of widely distributed organisms that lived during a geologically short period
19. the time needed for half of a sample of a radioactive substance to undergo radioactive decay to form daughter isotopes
21. One of the units of geologic time into which geologists divide eras
22. Change over time; the process by which modern organisms have descended from ancient organisms

1. A scientist who studies fossils to learn about organisms that live long ago
2. Type of fossil that is a hollow area in sediment in the shape of an organism or part of an organism
5. A fossil in which minerals replace all or part of an organism
6. The age of a rock compared to the ages of other rocks
7. One of the three long units of geologic time between the Precambrian and the present
9. Fossil that is a solid copy of an organism's shape, formed when minerals seep into a mold
11. the breakdown of a radioactive isotope into a stable isotope of the same element or a different isotope
12. Term used to refer to a group of related organisms that has died out and has no living members
14. The age of a rock given as the number of years since the rock formed
16. Break in Earth's crust along which rocks move
18. Geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it
20. Igneous rock layer that formed when magma hardens beneath earth's surface