Lab 3. Time and Ordering of Geologic Events

Lab 3. Time and Ordering of Geologic Events - Lab 3 Time...

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Lab 3 Time and Ordering of Geologic Events GEOL 1404-Historical Geology ------------------------------------------------------------------------------------------------------------------------------------------------- Relative dating Geologists track time with two types of dating, relative and absolute. Absolute dating gives us precise time measurements, whereas relative dating is relating one fact or event to another. Knowing that your father is older than you, but younger than your grandfather, is an example of relative dating . Before sophisticated methods of dating using radioactive isotopes developed, only relative dating could be used in the establishment of a geologic time scale. Moreover, placing geologic events in chronological order is crucial to field applications. Geologic events operate on time scales of millions of years, e.g. changes of rocks within the rock cycle. Recall that for sedimentary rocks to form, sediment must first be deposited. Naturally, a long time goes into depositing enough sediment to form a layer or stratum from which a rock can originate. A lot of the Earth’s surface is composed of depositional sequences of strata . Because of the movement of tectonic plates, crust can be deformed by way of folding or faulting. Folding causes horizontal strata to bend or even tilt. Faulting is the result of fracturing in a rock sequence. Other events include the injection or invasion of magma into other rocks. Large bodies of magma become batholiths after cooling. Thin igneous bodies that cut across overlying rock are dikes , and an igneous body that forms along a stratum is a sill . Contact metamorphism can occur in the surrounding rock (localized heating). An unconformity is a gap in the geologic record. It forms when erosion removes strata exposed at Earth’s surface, exposing older rocks underneath. These older rocks may get covered at a later time with younger strata. The contact between them is the unconformity. There are three kinds of unconformities.
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Lab 3. Time and Ordering of Geologic Events - Lab 3 Time...

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