Solution:
Carbon dating is only useful for relatively recent objects, it is more often used to date man-made. Fossils are dated using radiometric data from heavier elements like Uranium and by analysis of the strata in which they appear. Radiometric data is considered valid if several readings on the same object fall within a reasonable margin of error.
We use carbon dating because, Carbon dating only works on things that were once alive -- plant fossils, animal & human remains, etc.It works because when organisms are alive, they accumulate carbon during biological processes. Some of the carbon is carbon 14, a radioactive element whose ratio to normal carbon in living things is constant. When the organism dies, it stops accumulating carbon, and the carbon 14 decays radioactively with a half-life of about 5,700 years. It means 5,700 years after anything dies, there will be half as much carbon 14 as there was when it was alive. Measuring the ratio of carbon 14 to normal carbon in a fossil can give a pretty accurate measure of how long ago an organism died.