carbon-14 if often used for radioactive dating, but it has its limitations. uranium-238 or lead-206 are most often used to date rocks.

why would u-238 or pb-206 be more useful than c-14 when dating rocks?
a) rocks do not contain any carbon for dating purposes.
b) carbon-14's half-life is much too long to use for dating rocks.
c) the half life of carbon-14 is about 5700 years and is too short date rocks.
d) carbon-14 is only found in living things; it can only be used to date remains.

C) The half life of carbon-14 is about 5,700 years and is too short to date rocks

The half life of a substance is the time taken for half of that substance to decay. The earth, and so the rocks on and in it, are very old. Estimates place the earth to be 4-5 billion years old, which is why carbon-14 is unsuitable for the determination of the ages of rocks. The original quantities of carbon-14 present in the rocks will deplete to exceptionally low levels, meaning they can not be detected accurately. On the other hand, due to the longer half life of uranium, measurable quantities will be present.

Cin carbonh in hydrogeno in oxygen