The three vs of dating
So, if we find a rock with equal parts Potassium-40 and Argon-40, we know that half the Potassium-40 has decayed into Argon-40, and that the rock hardened 1.3 billion years ago.It’s hard to find rocks on the surface of the Earth that have not been altered over time.
As time passes, a rock will have more and more Argon-40 and less and less Potassium-40.Some isotopes have short half-lives of minutes or years, but Potassium-40 has a half-life of 1.3 billion years.Radiometric dating requires that one understand the initial ratio of the two elements in a given sample by some means.In your high school science classroom, you may have seen a large poster of the periodic table hanging on the wall.
The periodic table shows the types of atoms that make up the world around us.
The expansion of the universe gives an age for the universe as a whole: 13.8 billion years old.