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Posted by / 23-Jun-2017 08:37

What rocks are used for radiometric dating

You can then infer that the dino must have lived some time between these two age dates.

The discovery of radioactivity and the radiogenic decay of isotopes in the early part of the 20th century opened the way for dating rocks by an absolute, rather than relative, method.

It is therefore important to try to ensure that decay has taken place in a 'closed system', with no loss or addition of isotopes, by using only unweathered and unaltered material in analyses.

To calculate the age of a rock it is necessary to know the half-life of the radioactive decay series, the amount of the parent and daughter isotopes present in the rock when it formed, and the present proportions of these isotopes.The choice of method of determination of the age of the rock is governed by its age and the abundance of the appropriate elements in minerals.The samples of rock collected for radiometric dating are generally quite large (several kilograms) to eliminate inhomogeneities in the rock.However, sedimentary rocks can be age dated if a volcanic ash horizon or a diabase sill or dyke can be found within the sequence.For example, if you find a dinosaur bone in a sedimentary sequence and you find an ash layer 10 meter above the bone and another ash layer 20 meters below it, you can determine the age of the two ash layers.

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Up to this time estimates of the age of the Earth had been based on assumptions about rates of evolution, rates of deposition, the thermal behaviour of the Earth and the Sun or interpretation of religious scriptures.

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