Earth's History

4. A fossil that is a copy of an organism's shape, formed when minerals seep into a mold.
6. An igneous rock layer formed when magma hardens beneath Earth’s surface.
11. A record of the geological events and life forms in Earth’s history.
12. The geological 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.
13. One of the three long units of geologic time between the Precambrian and the present.
14. The preserved remains or traces of living things.
16. A fossil formed when an organism buried in sediment dissolves, leaving a hollow area.
17. The theory that the continents have moved over time.
18. An igneous rock layer formed when lava flows onto Earth’s surface and hardens.
19. One of the units of geologic time into which geologist divide eras.
21. A break or crack in Earth’s lithosphere along which the rocks move.
22. A place where an old, eroded rock surface is in contact with a newer rock layer.

1. Fossils of widely distributed organisms that lived during only one short period.
2. The breakdown of a radioactive element, releasing particles and energy.
3. A scientist who studies fossils to learn about organisms that lived long ago.
5. The age of a rock given as the number of years since the rock formed.
7. A type of fossil that provides evidence of the activities of ancient organisms.
8. The length of time needed for half of the atoms of a sample of a radioactive isotope to decay.
9. The age of a rock compared to the ages of rock layers.
10. The type of rock that is made of hardened sediment where fossils are found.
13. Describes a type of organism that no longer exists anywhere on Earth.
15. A type of fossil consisting of an extremely thin coating of carbon on rock.
20. A fossil in which minerals replace all or part of an organism.