Question

Why is radium still on Earth?

Answer 1

The reason that there is still detectable amounts of radium on earthis because radium is a decay product of naturally occurring uranium-238, which has a half life of about 4.5 billion years.

Answer 2

Since the half life of radium is 1600 years, the amount of radium on earth would be virtually undetectable if all the radium had continued decaying without some way to replenish it. The reason that there is still detectable amounts of radium on earth is because radium is a decay product of naturally occurring uranium-238, which has a half life of about 4.5 billion years.