Earth´s History

4. A fossilized structure such as a footprint or a coprolite, that formed in sedimentary rock by animal activity on or within soft sediment
6. A method of determining the absolute age of an object by comparing the relative percentages of a radioactive isotope and a stable isotope
8. Any method of determining whether an event or object is older or younger than other events or objects
10. Any method of measuring the age of an event or object in years
12. A long cylinder of ice obtained from, drilling through ice caps or ice sheets
14. The time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope

1. The process in which a radioactive isotope tends to break down into a stable isotope of the same element
2. A principle that states that younger rocks lie above older rocks if the luers have not been disturbed
3. A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time
5. A principle that geologic processes that occurred in the past can be explained by current geologic processes
7. The weather conditions in and area over a long period of time
9. The trace or remains of an organism that lived long ago, most commonly reserved in sedimentary rocks
11. An ordered arrangement of rock layers that is based on the relative ages of the rock and in which the oldest rocks are at the bottom
13. The scientific study of the origin, history, and structure if earth and the processes that shape Earth. The standard method used to divide Earthś long natural history into manageable parts