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Geologic Time
Introduction to Relative Dating
| Term | Definition |
|---|---|
| Relative Dating | is accomplished by placing events in a logical, sequential order. ex. "This is older than that." |
| Absolute Dating | provides specific dates for geologic rock units or events using radiometric dating. ex. "This rock is 14.3 million years old. |
| Geologic Time Scale | a world-wide time scale of Earth's history was established by the work of many geologists applying the principles of historical geology and correlating rocks of all ages throughout the world |
| Uniformitarianism | is a fundamental principle of geology: - this principle states that the laws of nature have remained unchanged through time and thus, that the processes observed today have also operated in the past, though possibly at different rate |
| Superposition | in an undisturbed succession of sedimentary layers, the oldest layer is on the bottom and the youngest layer is on the top |
| Original Horizontality | sediment (and some volcanic units) originally deposited in horizontal layer |
| Lateral Continuity | sediment extends laterally in all directions until it thins and pinches out or terminates against the edge of a depositional basin |
| Cross-cutting Relationships | James Hutton recognized that an igneous intrusion must be younger than the rock it intrudes - how to tell the difference between a buried lava flow and a sill |
| Principle of Inclusions | inclusions in a rock are older than the host roc |
| Principle of Fossil Succession | Principle of fossil succession - fossils vary vertically in a specific, predictable order - same fossils won't appear out of order Use index fossils to date sedimentary rocks - widespread/global - short-lived |
| Unconformities | surfaces of discontinuity in sediment deposition, which encompass significant periods of time |
| Hiatus | the interval of geologic time represented by the unconformity |
| Disconformity | - flat-lying sedimentary rock overlain by flat-lying sedimentary rock - separates younger from older sedimentary strata that are parallel to each other |
| Angular Unconformity | - tilted / folded sedimentary rock overlain by flat-lying sedimentary rock - an erosional surface on tilted or folded rocks, over which younger rocks were deposited |
| Nonconformity | - igneous or metamorphic rock overlain by flat- lying sedimentary rock - an erosional surface cut into igneous or metamorphic rocks and overlain by younger sedimentary rock |
| Relative Dating: Application | - the principles of relative dating can be used to reconstruct the geologic history of an area - although no specific dates can be applied, the relative sequence of events can be determined by using the principles of relative dating |
| Correlation | the demonstration of equivalency of rock units from one area to another |
| Radioactivity | discovered in the late 19th century by Marie and Pierre Curie |
| Atoms | smallest units of matter that retainthe characteristics of an element |
| Isotopes | - an element behave the same chemically but have different atomic mass numbers - some isotopes are radioactive and are useful for radiometric dating |
| Radioactive Decay | - the process in which an unstable atomic nucleus is spontaneously transformed into an atomic nucleus of a different element |
| Alpha Decay | a helium nucleus is released |
| Beta Decay | releases an electron from a neutron |
| Electron Capture | a proton captures an electron and becomes a neutron |
| Half-life | he time it takes for one-half of the original unstable radioactive parent element to decay to a new, more stable daughter element |
Created by:
user1115
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