| A | B |
|---|
| absolute age | the exact age of rocks |
| relative age | the age of rocks in comparison to the ages of other things |
| radiometric dating | also carbon dating; the age of rocks and fossils found by measuring the decay of certain isotopes contained |
| law of superposition | principle of superposition; in undisturbed layers of rock, the oldest rocks are always on the bottom and it gets younger toward the top |
| unconformities | gaps in rock sequences |
| angular unconformities | horizontal lines of sedimentary rock are tilted and uplifted |
| disconformity | layers of rock are missing and there is evidence of erosion within the layers of rock |
| nonconformity | metamorphic or igneous rocks are uplifted and eroded |
| mechanical weathering | physical weathering; rocks and soils are broken down by atmospheric conditions such as heat, water, ice and pressure |
| chemical weathering | atmospheric chemicals or biological weathering break down rocks, soils, and minerals; including when water causes chemical reactions with the minerals contained in the rocks |
| continental drift | the theory that continents move in relationship to each other |
| fossils | evidence of past life preserved in rock |
| fossil record | the complete body of fossils that show how species and ecosystems change over time |
| fossilized | the process of becoming a fossil |
| trace fossil | a fossilize mark that is formed in soft sediment by the movement or action of an animal |
| index fossil | a fossil found in a narrow time range but widely distributed around the earth |
| trilobites | an extinct marine organism |
| radiometric dating | measures the age of rocks and fossils based on the decay of certain isotopes they contain |
