Carbon dating sedimentary rock
Geologists have established a set of principles that can be applied to sedimentary and volcanic rocks that are exposed at the Earth's surface to determine the relative ages of geological events preserved in the rock record.For example, in the rocks exposed in the walls of the Grand Canyon (Figure 1) there are many horizontal layers, which are called strata.According to the Smithsonian Institute, using radiodating of sedimentary rock tells the date of formation of the original igneous rock, which, through the processes of weathering and erosion, formed the layers of the sedimentary rock.Radiodating determines the maximum age of sedimentary rock. Geological Survey states that it is possible to use Carbon-14 radiometric dating for sedimentary rock younger than 50,000 years by dating once living material from the sediment.If a layer of igneous rock forms on top of the sedimentary rock, scientists determine an age bracket for the rock sample, but not an absolute age. However, the relatively short half-life of approximately 5,730 years makes it inappropriate for older samples.For dating older materials, scientists use isotopes of other elements, some of which have a half-life of 106 billion years.The layers of rock at the base of the canyon were deposited first, and are thus older than the layers of rock exposed at the top (principle of superposition).In the Grand Canyon, the layers of strata are nearly horizontal.
Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.Layers that cut across other layers are younger than the layers they cut through (principle of cross-cutting relationships).The principle of superposition builds on the principle of original horizontality." First, the relative age of a fossil can be determined.Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event.
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Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.