A geochemist wants to date a layer of rock by looking at the radioactive decay o

Question

A geochemist wants to date a layer of rock by looking at the radioactive decay of Ur4+ to Pb2+. She decides to look at a sample of zircon, which takes one 4+ cation into its crystalline structure, rather than a sample of sphene, which takes both 4+ and 2+ cations into its structure. Which of the following best supports her reasoning?

A) Every Pb2+ atom detected in the zircon sample must be the result of radioactive decay, while some Pb2+ atoms found in sphene could have been incorporated during its formation.

B) If two different types of cations are present in a sample, it is possible that they are both undergoing radioactive decay, and she will not be able to separate the effects of the two.

C) Because zircon is simpler, the analysis will require fewer steps, minimizing the possible propagation of error.

D) Sphene has the capacity to trap the Pb2+ ions that result from radioactive decay; accurate radiometric dating requires the release of 100% of the daughter element.

Explanation / Answer

A

The geochemist did a great job by looking at a sample of zircon, which takes one 4+ cation into its crystalline structure because there might be some other Pb2+ present befrore the start of that particular layer of dating. One can also think of pre availability of the Pb2+ ions in the crystal which eventually lead to the wrong calculation of dating. So it is always advisable to reconfirm if before the dating any other same final product preaxists or not.

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