Absolute dating rocks

How do scientists date rocks and fossils?

Allmon and Robert M. Ross Answering this frequently encountered question in geology requires two separate steps. They correspond to two different ways that we express how old something or someone is in our everyday experience. When we ask how old an object or a person is, we can answer either with a number or by comparison to something or someone else. We can also give an age in numerical units, such as days, months, years, etc. Rocks that formed from sediment mud, sand, gravel are called sedimentary rocks. Such rocks are usually seen to be arranged in stacks of layers called strata.

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Geological time — 1. Relative age dating — 2. Geological time scale — 4. Geological maps. Absolute age dating deals with assigning actual dates in years before the present to rocks or geological events. Contrast this with relative age dating, which instead is concerned with determining the orders of events in Earth's past. The science of absolute age dating is known as geochronology and the fundamental method of geochronology is called radiometric dating.

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As we learned in the previous lesson, index fossils and superposition are effective methods of determining the relative age of objects. In other words, you can use superposition to tell you that one rock layer is older than another. But determining the absolute age of a substance its age in years is a much greater challenge.

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How old are rocks?

Relative dating is used to determine the relative order of past events by comparing the age of one object to another. This determines where in a timescale the object fits without finding its specific age; for example you could say you're older than your sister which tells us the order of your birth but we don't know what age either of you are. There are a few methods of relative dating, one of these methods is by studying the stratigraphy.

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