| A | B |
|---|
| atoms | smallest piece of element |
| Law of superposition | youngest layer on bottom |
| index fossil | help identify relative age of rocks |
| trace fossil | footprint tells about habits |
| amber | best preserved fossil |
| amber, tar, ice | preserved fossils |
| rock fossils | mold and casts, trace, carbon,petrified |
| radioactive decay | break down of unstable elements |
| carbon-14 | used to date rocks <50,000 yrs old |
| potassium-40 | used to date older rocks |
| absolute age | number in years |
| relative age | age compared to something else |
| fossil | once living organism preserved over time |
| ammonite | index fossil like a snail |
| trilobite | index fossil |
| sedimentary rock | rocks made of eroded materials |
| igneous rock | rock made from melted magma |
| element | 110 basic building blocks of the universe |
| uncomformity | interruption of horizontal layering of rock |
| intrusion | erruption of a younger vein of lava that has hardened in rock |
