Dating on earth summary
But in actual practice, we know neither the original ratios nor if the specimen has been contaminated and are forced to make what we hope are reasonable assumptions.
The tiny initial amount of C14, the relatively rapid rate of decay (the half-life of C14 is currently about 5700 years) and the ease with which samples can become contaminated make radiocarbon dating results for samples "older" than about 50,000 years effectively meaningless.
PROBLEMS WITH RADIOCARBON DATING During the last 30 years, a new method of determining C14/C12 ratios has been developed.
It uses accelerator mass spectrometry to determine the amounts of C14 and C12 in a small sample which is vaporised in the test.
Radioactive carbon (Carbon 14) is formed in the upper atmosphere as a byproduct of cosmic radiation.
Cosmic rays are positively charged atoms moving at enormous speeds.
The ions produced are forced into a magnetic field where the different mass of the carbon isotopes causes a different deflection, allowing the quantity of each isotope to be measured.
As the number of protons decides the chemical nature of an atom, the atom now behaves like a carbon atom.When they strike ordinary atoms in the upper atmosphere, the cosmic rays smash them apart. Some of these neutrons then collide with nitrogen atoms.This collision is less destructive than the initial collision that produced them.They found large variations in the radiocarbon 'dates' of objects of known age sent to 38 radiocarbon 'dating' laboratories around the world.Thirty-one of the labs gave results that the British group called unsatisfactory.