| A | B |
|---|
| fossil | preserved remains or traces of life; found only in sedimentary rock |
| index fossil | found over a large geographic area, but existed for only a brief period of time |
| radioactive decay | the change which takes place when radioactive isotopes breakdown |
| correlation | matchup of rock layers in different locations by age or rock types |
| orogeny | process of mountain building |
| uniformitarianism | principle that most geologic events of the past are similar to processes we observe in the present |
| superposition | principle that the oldest rock layers are generally found at the bottom of an outcrop |
| unconformity | a gap in the geologic record caused by erosion |
| igneous intrusion | molten, liquid (magma) rock pushed into cracks within the Earth; coarse-grained rock due to slow cooling |
| igneous extrusion | molten, liquid (lava) rock flowing out onto the Earth's surface; fine-grained rock due to rapid cooling |
| radioactive dating | method of determining the absolute age of an object using measurements of natural radioactivity |
| half-life | time required for one-half of an element's atoms to change into the decay product |
| geologic time scale | division of the history of the Earth |
| landscape | general shape of a region on the Earth's surface |
| uplifting forces | rising of the Earth's crust from forces within the Earth |
| leveling forces | lowering of the Earth's crust from processes of weathering, erosion and deposition |
| landscape regions | plains (or lowlands), plateaus (or uplands), mountains (or highlands) |
| isotope | different forms of the same element having different numbers of neutrons in their nucleus |
