Dating rocks with uranium 238

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Carbon-14 is present in the air, and is absorbed by plants during photosynthesis.When animals/people eat plant matter, they absorb the carbon-14 from the plants into their bodies.One method to date rocks, if you know their origins, is to compare their location to locations of other rocks of known age.Rocks found in the earth are usually older than the rocks found above them.The four isotopes are uranium-235, uranium-238, lead-207, and lead-206.

There are a number of techniques that might be used.Organic material that has not fossilized and does not exceed 70,000 years of age can be dated by Carbon dating techniques.Sedimentary rock can only be dated by its association with igneous and metamorphic rock.The reason for stopping at lead is because lead is not radioactive and will not change into a different element.It may sound straight-forward, but there are many variables that have to be considered.

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