Rutherford applied the principle of a radioactive elements’ half-life to studies of age determination of rocks by measuring the decay period of radium to lead-206. A half-life usually describes the decay of discrete entities, such as radioactive atoms. Evans, gave 5,568 ± 30 by weighting according to the inverse square of the errors quoted.In that case, it does not work to use the definition “half-life is the time required for exactly half of the entities to decay”. Radiocarbon Dating – Willard Libby Nobel Lecture, December 12, 1960 bombarding graphite with a strong deuteron beam from a cyclotron, the (d, p) reaction on the 13C present in the natural mixture gave enough radiocarbon for them to detect. However, within a year or two, as a result of researches in the laboratory of the author’s group at the Argonne Laboratory, and at the University of Chicago, together with a number of other teams, the value of 5568 yr was established; the radiocarbon dates have always been given on this basis, even though it is now known that it is some 3% low compared to the latest value of 5730 yr.Libby’s initial numerical challenge was the half-life decay process.Half-life (t½) is the amount of time required for a quantity to fall to half its value as measured at the beginning of the time period.The cautious Willard Libby sensibly decided to limited the accuracy of his model to two decimal places and thus defined the outer limit of Radiocarbon Dating to be 55,680 years.The final step to complete Willard’s World was to reverse engineer a carbon reservoir size that could plausibly contain 527,147,333,650 atoms of Carbon 14.In other words, the probability of a radioactive atom decaying within its half-life is 50%. id=ACC0336&num Pages=23&fp=N Half-life 5,730 ± 40 years Carbon-14, an isotope with a half-life of 5715 years, has been widely used to date such materials as wood, archaeological specimens, etc. One strange statistical quirk of the half-life probabilities is that the period of time needed to complete the radioactive decay process depends upon the size of the original population. Los Alamos National Laboratory Eventually, Willard Libby settled on “the value of 5568 yr” and “radiocarbon dates have always been given on this basis” to avoid confusion!
Radiocarbon Dating – Willard Libby Nobel Lecture, December 12, 1960 the numerous layers of assumptions, uncertainties and probabilities that underpin Willard’s World it is hardly surprising that Willard Libby thought his “good fortune in many stages of this research was most miraculous”.
The 1960 version of Willard’s World sets the carbon reservoir size at “about 8.5 grams of carbon per cm2” To return to radiocarbon dating – knowing that there are about 2 neutrons formed per square centimetre per second, each of which forms a carbon-14 atom, and assuming that the cosmic rays have been bombarding the atmosphere for a very long time in terms of the lifetime of carbon-14 (carbon-14 has a half-life of about 5,600 years) – we can see that a steady-state condition should have been established, in which the rate of formation of carbon-14 would be equal to the rate at which it disappears to reform nitrogen-14.
This allows us to calculate quantitatively how much carbon-14 should exist on earth (see Fig.
This means that humanity is using three and a half earths.
This political cartoon by Jeff Parker addresses this popular issue.