If you wanted to date a fossil that you think is representat

If you wanted to date a fossil that you think is representative of the earliest life on earth, which isotope would you use: uranium-238, carbon-14, or potassium-40? Explain your answer.

Solution

Half life of the three isotopes are as follows:

Uranium 238 to Lead 206 (half-life = 4.5 billion years)

Potassium 40 to Argon 40 (half-life = 1.3 billion years)

Carbon 14 to Nitrogen 14 (half-life = 5,570 years) - We can date fossils present some 50,000 years ago

Carbon and potassium can be used for living organisms because that are present in the life forms. But carbon 14 cannot used because of less half life period.

So in order to date the fossil which is representative of the earliest life on earth, Potassium 40 can be used. Because its half life relates to the age of origin of life forms on earth.