How to Determine the Age of a Fossil

The age of fossils are determined by carbon dating and by radioactive calculations. Since all living things are made up of carbon, the relative age of fossils, which were once live animal or plant life, can be calculated by estimating at what time the fossil was alive. When the sun’s rays shine on the animals or plants and when this collides with nitrogen it creates Carbon 14, a radioisotope. 

People, as an example, have both Carbon-12 and Carbon 14 in their bodies, and as they age, this increases. Carbon-14 decays. Its half life is 5,700 years. That means that carbon-14 remnants will still be measurable when compared with the ratio of how this has diminished to the constant amount of Carbon 12 that remains constant. The findings are then compared to a what a normal living organism’s carbon content should be, and the normal age of a fossil is determined.

This method of calculating the age of fossils is not unlike that of learning the age of a tree by its many rings. The earth is layered by sedimentary soil and fossilized materials as it ages. This can be seen along many newly built mountainous highways where various layers of rock, minerals, and vegetative materials are exposed to the human eye as the mountains have been cut through to make passageways.

Thus in fossil dating, the layer of the earth in which the fossil was found will be important in finding the age. Once a working model has been found, this can be used to compare similar fossils. Of course, it is not absolute mathematics, but it serves as a fairly close approximation.

There are limits. Fossils that are older than 50,000 years cannot be carbon dated directly. All their carbon will have dissipated. Therefore the best method is using geologic layers to determine the age of the rock.  In other words, in what layer, what type of rock was the fossil found?

Further research at the University of Berkeley on-line shows two different kinds of fossil and rock dating: The first method, calculations based on geological layers and the fossils found in them; the second method, “radio age dating,”  measuring the amount of radioactive decay is a recent 20th century method.

With this new knowledge, it is possible to get a fairly accurate age of fossils. Yet this fascination is fairly new, about a hundred years old, actually. Frank Libby, a chemist who worked with the Manhattan Project during World War II is credited with radioactive dating, that is dating materials that had once been alive. This of course includes fossils, of animal and plant life. Mostly, of course plant life would have decayed, but leaf fossils do remain if they were immediately covered by volcanic ash that preserved them from rot.  

What made this discovery of Libby’s possible was the vast amount of work that had gone on before. In particular, two important events: “In 1903, Sir Ernest Rutherford (1871-1937) along with Frederick Soddy (1877-1956) identified the phenomenon of radioactive half-life decay, and the discovery of carbon 14 in 1940 by Martin David Karmen and Sam Ruben.”

An interesting new science developing, that of the new discovering the old. Wonder what another hundred years will add to the stash of knowledge about what has gone on before? Add to that the knowledge that everything that ever was, still is, but is in another form. The few leaves that escaped the transformation by being preserved by some chemical action that possibly caught them as they floated downward, or forests of trees petrified into rocks, make for exciting adventures of discovery.

Yet the fact of not seeing does in no way change a grain of sand as it wanders on from day to day, carried out to sea of one receding ocean, only to be deposited on another and another until it finally becomes part of a sandstone. It may stay this way for millenniums until it once again gets smashed into sand, a grain swallowed by an oyster where it grates and grinds along with other bits of sand, until a beautiful pearl has been created.  The interesting part is that it is all still around, even though shuffled from here to there. The moral of that is everything is useful in some way, known or unknown, old or new.