Why is it that carbon out of so many element can be use in determining the age of something?

Question

Why is it that carbon out of so many element can be use in determining the age of something?

Answer 1

Two points here.  Firstly, carbon is convenient for dating things that were once living because living things absorb carbon 14 from the environment.  Carbon 14 is radioactive, and decays with a half life of about 5730 years, so it is convenient for dating stuff that is up to a few tens of thousands of years old.   Secondly, any process that causes a separation of something over time can be used for dating things; dozens of such have been used, involving many different elements and varying processes, some of which involve radioactive species and many which don't.  Among the more interesting recent results: the earth is 4566 million years old; the sun is older by 2.5 million years, and the present oxygen atmosphere of the earth dates back about 2700 million years.

Answer 2

That's because carbon in an integral part of what they are measuring the age of.  Carbon-14 dating can only be used for determining the age of organic substances that contain carbon.  All "carbon-based lifeforms", you include, contain C-14, which decays at a known rate with a half-life of around 5000 years.  Therefore, things as old as 50,000 years can be dated.