Green plants absorb the carbon dioxide, so the population of carbon-14 molecules is continually replenished until the plant dies.
Carbon-14 is also passed onto the animals that eat those plants.
By examining the object's relation to layers of deposits in the area, and by comparing the object to others found at the site, archaeologists can estimate when the object arrived at the site.
Unfortunately, a lot of misinformation about radiocarbon dating has been circulated by individuals who have neither training nor hands-on experience in this area.
The whole validity of radiocarbon dating for the past 10,000 years---the time span of interest to biblical chronology---hangs only on the tree-ring chronologies which are used to calibrate it. .) This process does not involve any assumption about historic radiocarbon to stable carbon ratios because the radiocarbon concentration in the tree-ring samples would be affected in exactly the same way as the radiocarbon concentration in the specimen to be dated. To quote again from The Answers Book: Some recent, though controversial, research has raised the interesting suggestion that c (the speed of light) has decreased in historical times. If it is correct, then radioactive decay rates would automatically be affected, and would show artifically high ages.
(Ham et al., page 72.) As with Assertion 1, Assertion 2 fails to account for the tree-ring calibration which is a routine part of modern radiocarbon dating.
But while the difficulties of single life may be intractable, the challenge of determining the age of prehistoric artifacts and fossils is greatly aided by measuring certain radioactive isotopes.
Until this century, relative dating was the only technique for identifying the age of a truly ancient object.