| Term | Definition |
|---|
| Relative Dating | method to determine the order of events and relative age of rocks by examining the position of rocks in a sequence |
| Principle of Original Horizontality | layers of sediment that are generally deposited in a horizontal or nearly horizontal position |
| Law of Superposition | in undisturbed rock layers, the oldest rocks are on the bottom and the youngest rocks are on the top |
| Principle of Cross-Cutting Relationships | a feature such as a fault or intrusion that cuts across layers is younger than the layers it cuts across |
| Strata | Layers of rock |
| Igneous Intrusion | magma cutting through formed layers of sedimentary rock that then cools and hardens |
| Unconformity | A surface that represents a gap in the rock record, caused by erosion or lack of deposition |
| Correlation | establishing the equivalence of rocks of similar age in different areas |
| Fossil | The preserved remains or traces of an organism that lived in the past |
| Index Fossil | remains of species that existed on earth for a relatively short period of time, were abundant and wide spread geographically, and can be used by geologists to assign the ages of rock layers |
| Absolute Age Dating | uses radioactive decay to determine an exact age of a rock or fossil |
| Half-Life | the time it takes for half of the nuclei in an unstable isotope to decay into a stable daughter product |
| Radiometric Dating | the process of measuring the absolute age of geologic material by measuring the concentrations of radioactive isotopes and their decay products |
| Radiocarbon Dating | a chemical analysis used to determine the age of organic materials based on their content of the radioisotope carbon-14 |
| Isotope | atoms of the same element that have different numbers of neutrons in the nucleus |
| Parent Isotope | an unstable radioactive isotope |
| Daughter Product | radioactive decay resulting from the parent isotope |
| Radioactivity | the process by which some nuclei spontaneously split and emit particles. |
| Geologic Time Scale | a record of the geologic events and life forms in earth's history |
| Uniformitarianism | is the idea that the geologic processes that operate today also operated in the past |
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