Why is there still Carbon 12 left?

Question

99% of the Carbon on Earth is of the isotope Carbon 12, which has a half life of 50,000 years. Since the Earth is 4.5 billion years old, why is there still so much of it left? Wouldn't there be just a small fraction of it left? This may sound like a dumb question, but I've always wondered. Also, what happens to it when it decays and becomes radioactive?

Answer 1

I can't find anything that talks about the half-life of Carbon 12. Every reference I've checked says that Carbon 12 as well as Carbon 13 are stable. Carbon 14, however, has a half-life of about 5700 years.

If Carbon 12 had a half-life of 50,000 years, your question would have nuclear scientists scratching their head and hiding from the press all over the world! Great point. I did read that Carbon 14 dating is only considered reliable for things up to about 60,000 years. Maybe that's the number you saw?

A Carbon 14 nucleus has 6 protons and 8 neutrons. When one of it's neutrons decays, it becomes a proton and a free electron, which is shot out as "beta radiation". Now there are 7 protons and 7 neutrons, which makes it a common Nitrogen nucleus. Carbon 14 is made in the upper atmosphere when a high speed neutron crashes into a Nitrogen nucleus and replaces a proton that got kicked out by the collision. The nuclear reaction looks like this:

1n + 14N → 14C + 1p

Carbon 14 is more or less just a transformed Nitrogen atom that eventually reverts back to it's original state later on.

Answer 2

Carbon-12 is the more abundant of the two stable isotopes of the element carbon, accounting for 98.89% of carbon. It contains 6 protons, 6 neutrons and 6 electrons. It still exists, and is in abundance.

Answer 3

Carbon-12 is stable, which means it doesn't decay into anything else. Who told you it has a half-life of only 50,000 years?

Answer 4

Hi. Carbon 12 is a stable element. Carbon 14 is the element you are talking about (I think).