Perhaps no concept in science is as misunderstood as "carbon dating." Almost everyone thinks carbon dating speaks of millions or billions of years.But, carbon dating can't be used to date either rocks or fossils.This argument was popularized by Henry Morris (1974, p.164), who used some calculations done in 1968 by Melvin Cook to get the 10,000-year figure. Whitelaw, using a greater ratio of carbon-14 production to decay, concluded that only 5000 years passed since carbon-14 started forming in the atmosphere!The argument may be compared to filling a barrel which has numerous small holes in its sides.We stick the garden hose in and turn it on full blast.The water coming out of the hose is analogous to the continuous production of carbon-14 atoms in the upper atmosphere.Thus the ratio of stable C-12 to unstable C-14, which is known in today's open environment, changes over time in an isolated specimen. As long as the tree lives, it absorbs carbon from the atmosphere in the form of carbon dioxide, both C-12 and C-14.Once the tree dies, it ceases to take in new carbon, and any C-14 present begins to decay.
The water leaking out the sides of the barrel represents the loss (mainly by radioactive decay) of the atmosphere's supply of carbon-14.
The following material has been taken from a sheet entitled Several Faulty Assumptions Are Used in all Radiometric Dating Methods.