Across
- 1. The amount of time it takes for half of a remaining isotope to decay to a daughter product.
- 8. The disappearance of all members of a species from Earth.
- 9. States that any rock or fragment that's included inside of another rock is older than the rock in which it is included.
- 10. The largest division of geologic time.
- 11. A long and distinct period of history with a particular feature or characteristic; within the Phanerozoic: Paleozoic, Mesozoic, and Cenozoic.
Down
- 2. States that any feature that cuts across a sequence of rocks is younger than everything it cuts through.
- 3. The summary of Earth's history divided into intervals of time defined by major events or changes on Earth.
- 4. States that in an undisturbed sequence of rocks, each layer is younger than the one below it but older than the one above it.
- 5. Are useful for dating and correlating the strata in which it is found.
- 6. Divisions of periods (which are the major divisions of eras) in geologic time.
- 7. One of the units of geologic time into which geologists divide eras.