| A | B |
|---|
| fossils | the remains or traces of prehistoric life |
| unaltered remains | some remains have not be changed over time |
| altered remains | the remains of an organism are changed over time |
| carbonization | occurs when an organism is buried under fine sediment |
| trace fossils | indirect evidence of prehistoric life |
| 2 conditions important for preservation | rapid burial and possession of hard parts |
| princple of fossil succession | fossil organisms succeed one another in a definite and determinable order |
| index fossils | are widespread geographically, limited to a short span of geologic time, and occur in large numbers. |
| atomic number | number of protons in the atom's nucleus |
| mass number | number of protons plus the number of neutrons in an atom's nucleus |
| radioactivity | spontaneous decay of certain unstable atomic nuclei |
| half-life | amount of time necessary for one-half of the nuclei in a sample to decay to a stable isotope. |
| radiometric dating | procedure of calculating the absolute ages of rocks and minerals that contain radioactive isotopes |
| radioactive dating | method for determining age by comparing the amount of carbon-12 in a sample |
| eons | represents the greatest expanses of time |
| eras | eons are divided into ERAS |
| epochs | eras are divided into EPOCHS |
