Isotopes are simply different atoms with the same chemical behavior (isotope means “same type”) but with different masses. This works because during photosynthesis, trees take up carbon from the atmosphere and lay this carbon down as plant organic material in the form of rings, providing a snapshot of the atmospheric composition of that time. This isn’t to say that the tree rings have the same isotopic composition as the atmosphere – as noted above, plants have a preference for the lighter isotopes, but as long as that preference doesn’t change much, the tree-ring changes wiil track the atmospheric changes.
Sequences of annual tree rings going back thousands of years have now been analyzed for their C ratio of surface ocean waters.
Experts answer this in three ways: 1) the fossils "downwashed" through solid rock to lower levels, 2) say they "reworked" themselves to lower strata; that is, they slipped, slid, or fell through the solid rock, 3) or just ignore the fact.
The point is, specimens are often found buried in areas where they cannot be dated by surrounding strata However, two things need to be considered: 1) When digging up a tree branch, taking a specimen from an ancient ruin, or uncovering some object, how does one determine how old it is before measuring to determine whether it is older than the Industrial Revolution?
Later Scientists have done the same with the nuclear weapons.
Wood found in the ground is usually considered a certain age based on what strata it is found in, however, sometimes (more often than believed), specimens are found far below the strata where they are first supposed to have evolved into existence.
It should be pointed out that Libby was a smart guy and accounted for this discrepancy.
This is calculated through careful measurement of the residual activity (per gram C) remaining in a sample whose age is Unknown, compared with the activity present in Modern and Background samples. Thus 1950, is year 0 BP by convention in radiocarbon dating and is deemed to be the 'present'.
You can get an idea of the relationship between C14 and age at the Carbon Dating calculator page. 1950 was chosen for no particular reason other than to honour the publication of the first radiocarbon dates calculated in December 1949 (Taylor, 19).
Radiocarbon dating uses the naturally occurring isotope Carbon-14 to approximate the age of organic materials. Often, archaeologists use graves and plant remains to date sites.
Since its conception by Willard Libby in 1949, it has been invaluable to the discipline.