| A | B |
|---|
| relative age | age of rocks or geologic events compared to other rocks or events |
| absolute age | actual age of rocks or events in years |
| principle of superposition | states that in a column of undisturbed sed. rock layers, the oldest rocks will be at the bottom and the youngest will be at the top |
| intrusion | a mass of igneous rocks that have cooled beneath the earth's surface |
| extrusion | a mass of igneous rocks that cooled at the earth's surface |
| joint | a crack in rocks along which no movement has taken place |
| vein | a mineral deposit in rocks formed from minerals that were once dissolved in water. |
| correlation | process of showing that rocks or events in different places are of the same relative or absolute age |
| outcrop | bedrock exposed at the surface |
| bedrock | solid rock |
| walking the outcrop | walking along the exposed bedrock |
| fossil | remains or evidence of past life on earth |
| index fossil | a fossil of an organism that lived over a wide area for a short time period |
| geologic time scale | chronologic model of the history of the earth |
| unconformity | buried erosional surface |
| uniformitarianism | theory that geologic events of the present are the same as they were in the past |
| isotope | atom of an element having a different number of neutrons |
| radioactive decay | decay of a heavy nucleus into lighter nuclei |
| half-life | the time it takes for one-half of a sample of a radioactive material to decay |
| strike | compass direction along which an out crop runs |
