Lab 2_SurfaceDating - Lab 2: Planetary Surfaces &...

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Geology and the study of planetary surfaces is a study of the history of formation and evolution of rock units, and therefore one of the primary tasks of a geologist is to interpret the sequence of events represented on a geologic map and/or cross section . The purpose of this part of the lab is to introduce you to reading the record in planetary surfaces. Relative Ages and Dating Relative dating provides a sequence of events by determining which rock unit or geologic structure is younger than the other units or structures. In order to determine the history of a planetary surface, we must determine the relative ages of the different units and structures. This involves using some simple rules to specify whether a rock unit or structure is older or younger than another. NOTE: Relative dating does not provide an age for the units and events in years, millions or billions of years. An age that we can define in terms of a specific number of year is called an absolute age . Relative ages are commonly assigned names, as in the geological time scale: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, etc. These names are applied to groups of rocks that can be shown to have formed during the same geological time period. The names typically refer to something about the geographic region or rock property of the rock units that were first described to define this time period. Relative age names have been assigned to many planetary surfaces, following similar processes to those used to create Earth's geological time scale, but each planet has its own series of names . In general, these names describe a series of surface rock that share similar characteristics and can be identified to have formed within the same time period. Absolute ages of the time periods may not be able to be determined, and the time periods are unlikely to be the same for different planetary bodies. Thus, even when absolute ages are determined, the use of names for surfaces or rocks defined by relative ages remains useful. Although the name relative age may sound somewhat imprecise, after a relative age has been firmly established, it is unlikely to change. Most of Earth's geological time scale was determined over a hundred years ago and although it has been further subdivided, the established relative ages remain unchanged. The assignment of absolute ages to the time scale by radiometric dating has confirmed the validity of the relative ages. However, absolute ages are subject to change as the radiometric decay constants from which they are calculated are refined (we'll look at this in a later lab). Principle of Superposition Perhaps the most powerful method of determining relative ages is the Principle of Superposition . This is a natural law which states that for rocks deposited on the surface , whatever rock unit is on top is the youngest. The law is derived from the deduction that
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Lab 2_SurfaceDating - Lab 2: Planetary Surfaces &...

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