A Carbon-14 Coincidence

A Carbon-14 Coincidence

Why does the Moon have almost exactly the same apparent size in the sky as the Sun, so that it perfectly blocks out the Sun in a solar eclipse?

A few weeks back I mentioned the benefits to scientific discovery provided by this coincidence. By using it, astronomers learned about the Sun’s corona, were able to test Einstein’s general theory of relativity, and determined the past rotation rate of the Earth, all at a time earlier than would have been otherwise impossible. While there is no scientific reason for this remarkable coincidence, it suggests that God may have provided it as a tool so that we could more quickly discover characteristics of His creation.

Another coincidence has provided archeologists and paleontologists with an extraordinary tool for dating objects that contain carbonaceous material. I speak of carbon-14 with its just-right-for-dating half-life of 5,730 years. This coincidence is remarkable because C-14, along with the inert C-12, not only is an important component of fossils, but if C-14 had a longer half-life, it wouldn’tt provide the accuracy for more recent fossils; if shorter, it wouldn’t work for longer time periods.

In a paper published in the latest issue of Physical Review Letters (available in preprint here and as a news summary here), Jeremy Holt and colleagues note in their introduction that C-14 was not expected to have a long half-life. Based on previous models, physicists expected it to have a similar half-life to that of C-11 at 20 minutes, or of oxygen-14 at 1 minute, or O-15 at 2 minutes, or that of nitrogen-13 at 10 minutes. Why does C-14 have a half-life of 3 billion minutes? This has been a mystery to theorists for half a century.

However, in a breakthrough discovery, Holt and his collaborators have performed a new calculation that includes the change of the meson mass as it travels through an atomic nucleus. Mesons are atomic particles that are believed to mediate the force between two nuclei, and play a role in the radioactive process taking place in C-14. From these calculations the authors were able to account for why C-14, but not the other nuclei, has this long radioactive half-life.

Radiocarbon dating is a method that depends on the naturally occurring presence of C-14 in the material to be dated. Every living thing constantly exchanges C-14 with its environment as long as it lives. Once it dies, the exchange stops. Consequently, scientists assume that a fossil’s C-14 content does not change once the sample to be dated ceases to incorporate carbon, except for the amount gradually depleted radioactively with its 5,730-year half-life. If the amount present when its activity ceased can be determined, then the ratio of the initial amount to the existing amount is related to how long ago it was alive. While scientists must account for misuse of this technique and use proper calibration, in most cases it can provide a very accurate way to date many fossil samples containing carbon.

Radiocarbon dating is an important tool that has yielded rich insight into the events and processes in Earth’s history. Because many of the key truth-claims of the Bible are rooted in history, this technique has also provided support for their veracity.