In earth's upper atmosphere, on the edge of what is commonly called outer space, light atomic nuclei from unknown sources outside of our solar system traveling at speeds approaching the speed of light called rain down continuously.
These highly energetic nuclear bullets wreak havoc on the atoms in the upper atmosphere: tearing electrons from their orbitals and setting them free, knocking neutrons and protons from the tight confines of the nucleus and setting them free, generating x-rays and gamma rays as they decelerate, and creating exotic particles like muons and pions directly from their excessive kinetic energy.
The isotopic distribution of carbon on the Earth is roughly 99% carbon 12 (with 6 protons and 6 neutrons) and 1% carbon 13 (with 6 protons and 7 neutrons).
These isotopes are stable, which is why they are with us today, but unstable isotopes are also present in minute amounts.
By the end of the Twentieth Century, humans were adding carbon from fossil fuels to the atmosphere at a rate of about 10 billion tonnes per year (10 kg) a few years into the Twenty-first Century.
Fossil fuels are the remains of long dead plants that were buried in sediment tens to hundreds of millions of years ago (coal being made primarily from land plants and petroleum from plankton and algae). Drinking ethanol (which is usually just called alcohol) is made from the fermented sugars of plants (grains like barley, wheat, rye corn, or rice; fruits like grapes or apples; vegetables like sugarcane or agave; or the nectar of plants collected by bees called honey). The carbon in the ethanol that came from plants will be relatively rich in C are not.
Likewise, when Ar "dating" was attempted on Proterozoic granulite-facies rocks in the Fraser Range (western Australia) and Strangways Range (central Australia), it was found that garnet, sapphirine, and quartz contained excess was probably incorporated at the time of the formation of the minerals, and calculations suggested a partial pressure of ~0.1 atm Ar in the Proterozoic lower crust of Australia, which extends over half the continent.
Die Wissenschaft kann diese Uhr ablesen und so das Alter eines Fundes ermitteln. Source unknown — possibly das Museum für Vor‑ und Frühgeschichte (the Museum for pre‑ and early history) in Berlin.
Every time a living being dies a stopwatch starts ticking. is used to determine the age of previously living things based on the abundance of an unstable isotope of carbon.
A timber found in a home built 5730 years ago (one half life) would have half the C in the Earth's atmosphere has remained constant.
As a first approximation one can assume this, but more accurate results must take into account fluctuations in the intensity of the cosmic rays entering the Earth's atmosphere.
This is approximately 2,500 times as much Ar as is found in natural muscovite.