Shall I try? Pete, ordinary carbon has an indefinite lifespan. There's ordinary carbon around that was formed not long after the Big Bang (and don't start...) Carbon 14 is a radioactive isotope of carbon. It's an unstable variety of carbon that breaks down over tens of thousands of years until it isn't carbon 14 any more. Most carbon, though, is not carbon 14, so we're safe. Carbon 14 is constantly being formed, taken in by living things (because plants use carbon dioxide from the air, and some of that carbon dioxide will have carbon 14 in it instead of ordinary carbon - then we eat the plants, etc...) and breaking down. When you die, you stop taking in carbon 14, so the level of carbon 14 in your body slowly falls as it breaks down. The amount left in your body is an accurate measure of how long ago you died, because it breaks down at a very steady rate. This is useful up to about 60,000 years after the creature died. After that, there isn't enough carbon 14 left to give a reliable measure any more. But none of this has anything to do with diamonds, etc. They are made of nearly all ordinary carbon, as they are very old and any carbon 14 they had to start with has virtually all broken down. Cheers.