Determining absolute ages by radiometric dating

Look for “absoluteages such as cornerstones, dates carved into fresh concrete, or dates stamped on manhole covers.

I also like this simple exercise, a spin-off from an activity described on the USGS site above.

Take students on a neighborhood walk and see what you can observe about age dates around you.

The narrower a range of time that an animal lived, the better it is as an index of a specific time.

No bones about it, fossils are important age markers.

To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This rule is common sense, but it serves as a powerful reference point.

Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.For example, which is older, the bricks in a building or the building itself?Are there repairs or cracks in the sidewalk that came after the sidewalk was built?Geologists often need to know the age of material that they find.They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years.In a way this field, called geochronology, is some of the purest detective work earth scientists do.

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