Isochron dating calculator
Creationists also attack radioactive dating with the argument that half-lives were different in the past than they are at present. There is no more reason to believe that than to believe that at some time in the past iron did not rust and wood did not burn.
Furthermore, astronomical data show that radioactive half-lives in elements in stars billions of light years away is the same as presently measured. On pages and of The Genesis Flood, creationist authors Whitcomb and Morris present an argument to try to convince the reader that ages of mineral specimens determined by radioactivity measurements are much greater than the "true" i.
The mathematical procedures employed are totally inconsistent with reality. Henry Morris has a PhD in Hydraulic Engineering, so it would seem that he would know better than to author such nonsense. Apparently, he did know better, because he qualifies the exposition in a footnote stating:. This discussion is not meant to be an exact exposition of radiogenic age computation; the relation is mathematically more complicated than the direct proportion assumed for the illustration. Nevertheless, the principles described are substantially applicable to the actual relationship. Morris states that the production rate of an element formed by radioactive decay is constant with time.
This is not true, although for a short period of time compared to the length of the half life the change in production rate may be very small. Radioactive elements decay by half-lives. At the end of the first half life, only half of the radioactive element remains, and therefore the production rate of the element formed by radioactive decay will be only half of what it was at the beginning. The authors state on p.
If these elements existed also as the result of direct creation, it is reasonable to assume that they existed in these same proportions. Say, then, that their initial amounts are represented by quantities of A and cA respectively.
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Morris makes a number of unsupported assumptions: This is not correct; radioactive elements decay by half lives, as explained in the first paragraphs of this post. There is absolutely no evidence to support this assumption, and a great deal of evidence that electromagnetic radiation does not affect the rate of decay of terrestrial radioactive elements. He sums it up with the equations: He then calculates an "age" for the first element by dividing its quantity by its decay rate, R; and an "age" for the second element by dividing its quantity by its decay rate, cR.
It's obvious from the above two equations that the result shows the same age for both elements, which is: Of course, the mathematics are completely wrong. The correct relation can obtained by rearranging the equation given at the beginning of this post: For a half life of years, the following table shows the fraction remaining for various time periods:.
By way of contrast, the following table displays the incorrect values calculated on the basis of the Morris straight line relationship: In all his mathematics, R is taken as a constant value. We may therefore set R as equal to the initial rate in the above table:. Calculating, using the Morris equation: Morris' equations would indicate that after years the amount of parent element would be completely gone, but the daughter element would nevertheless continue to be formed!
Click on the web site of Dr. Roger Wiens of Cal Tech for a detailed analysis of the accuracy of radioactive dating. Additional information is also available in talk. That's why we know the ratio of the strontium isotopes in the melt is a horizontal straight line in the illustration above.
The isotope 86 Sr is non-radiogenic in origin and does not change, but 87 Sr is produced by the radioactive decay of 87 Rb. There is no way of anticipating what the 87 Sr is at the time of melt, but if there is 87 Rb present then it will increase with time as the rubidium isotope decays. That is what makes this a useful clock. Rubidium-strontium isochrons will be formed at any time after crystallization of a rock provided the initial conditions are met. Different minerals which make up the rock will in general include different amounts of rubidium 87 Rb in their structures, and those which have more rubidium at the time of crystallization will have more radioactive decays and gain more of the daughter product 87 Sr.
The precise nature of the radioactive decay process predicts that all the minerals should lie along a straight line, an isochron. Indeed, the initial amount of the daughter product can be determined using isochron dating. This technique can be applied if the daughter element has at least one stable isotope other than the daughter isotope into which the parent nuclide decays.
All forms of isochron dating assume that the source of the rock or rocks contained unknown amounts of both radiogenic and non-radiogenic isotopes of the daughter element, along with some amount of the parent nuclide. Thus, at the moment of crystallization, the ratio of the concentration of the radiogenic isotope of the daughter element to that of the non-radiogenic isotope is some value independent of the concentration of the parent.
As time goes on, some amount of the parent decays into the radiogenic isotope of the daughter, increasing the ratio of the concentration of the radiogenic isotope to that of the daughter. The greater the initial concentration of the parent, the greater the concentration of the radiogenic daughter isotope will be at some particular time. Thus, the ratio of the daughter to non-radiogenic isotope will become larger with time, while the ratio of parent to daughter will become smaller.
To perform dating, a rock is crushed to a fine powder, and minerals are separated by various physical and magnetic means. Each mineral has different ratios between parent and daughter concentrations. For each mineral, the ratios are related by the following equation:. The proof of 1 amounts to simple algebraic manipulation. It is useful in this form because it exhibits the relationship between quantities that actually exist at present. Ratios are used instead of absolute concentrations because mass spectrometers usually measure the former rather than the latter.