1. 17-1 the Fossil Record

2. Paleontologist Scientists who studies fossils

3. Fossil record Information about past life, including the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived

4. Extinct Term used to refer to a species that has died out

5. Relative dating Method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock.

6. Index fossil Distinctive fossil used to compare the relative ages of fossils

7. Half-life Length of time required for half the radioactive atoms in a sample to decay

8. Radioactive Dating Technique in which scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.

9. Geologic time scale Scale used by paleontologist to represent evolutionary time.

10. era One of several subdivisions of the time between the Precambrian and the present

11. Period Unit time into which eras are subdivided

12. Key Concept The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms, including species, have changed over time.

13. Key concept Relative dating allows paleontologists to estimate a fossil’s age compared with that of other fossils.

14. Key concept In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.

15. Key Concept After Precambrian Time, the basic divisions of the geologic time scale are eras and periods.