The last figure I heard was that there are currently eight nuclear subs on our ocean floors. It doesn't work for sea creatures and other things that are under water. Then they measure how much is left in the specimen when they find it.
It comes from cosmic rays that rain down on the earth (and us) from outer space.
One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains from archaeological sites.
Carbon has two stable, nonradioactive isotopes: carbon-12 (12C) and carbon-13 (13C).
There are also trace amounts of the unstable radioisotope carbon-14 (14C) on Earth.
After plants die or are consumed by other organisms, the incorporation of all carbon isotopes, including 14C, stops.
Carbon-14 has a relatively short half-life of 5,730 years, meaning that the fraction of carbon-14 in a sample is halved over the course of 5,730 years due to radioactive decay to nitrogen-14.The carbon-14 isotope would vanish from Earth's atmosphere in less than a million years were it not for the constant influx of cosmic rays interacting with molecules of nitrogen (N) into organic compounds during photosynthesis, the resulting fraction of the isotope 14C in the plant tissue will match the fraction of the isotope in the atmosphere.