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.

What do uranium-238, carbon-14, and potassium-40 all have in common?

You have a rock that was formed at the same time as the Earth was formed. How old is the rock? How much of the original uranium-238 is likely to be left today in that rock?

Solution

We will use Uranium 238 due to its long half life i.e. 4.5 billion years, and it transmutes to lead 206 which is a stable end product. carbon 14 is not used as its half life is approximately 5730 years and because of the short half life it cannot be used to date old fossils. Potassium has half life of 1.3 billion years therefore the oldest can be dated by Uranium.

All the three is used inRaiometric decay.

Ancient rocks measuring 3.5 billion years of age are found on the Continents. Earths oldest rocks have been destroyed /recycled by the process of plate tectonic. Half of the eoriginal amount of uranium will be present as the hals life is 4.3 billion years.