An example of this can be found in Strahler, Fig If the strontium isotope was not present in the mineral at the time it was formed from the molten magma, then the geometry of the plotted isochron lines requires that they all intersect the origin, as shown in figure However, if strontium 87 was present in the mineral when it was first formed from molten magma, that amount will be shown by an intercept of the isochron lines on the y-axis, as shown in Fig Thus it is possible to correct for strontium initially present. The age of the sample can be obtained by choosing the origin at the y intercept.
Note that the amounts of rubidium 87 and strontium 87 are given as ratios to an inert isotope, strontium However, in calculating the ratio of Rb87 to Sr87, we can use a simple analytical geometry solution to the plotted data. Again referring to Fig. Since the half-life of Rb87 is When properly carried out, radioactive dating test procedures have shown consistent and close agreement among the various methods.
If the same result is obtained sample after sample, using different test procedures based on different decay sequences, and carried out by different laboratories, that is a pretty good indication that the age determinations are accurate. Of course, test procedures, like anything else, can be screwed up. Mistakes can be made at the time a procedure is first being developed. Creationists seize upon any isolated reports of improperly run tests and try to categorize them as representing general shortcomings of the test procedure.
This like saying if my watch isn't running, then all watches are useless for keeping time. 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.
What is Radioactive Dating? - Definition & Facts
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. 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. Isochron Dating and Age of Earth. These are both isotopes of the element carbon present in a constant ratio while an organism is living; however, once an organism dies, the ratio of carbon decreases as the isotope deteriorates. Radiocarbon dating can only be used to date items back to as far as about 50, years old.
Radiocarbon dating was used to identify a forged painting based upon the concentrations of carbon detected on the canvas within the atmosphere at the time that the picture was painted. So, to sum this all up, radioactive dating is the process scientists use to conclude the ages of substances dating back several to many years ago by using the isotopes of elements and their half-lives. An isotope is a variation of an element based upon the number of neutrons.
The disintegration of the neutrons within the atom of the element's nucleus is what scientists call radioactivity. An isotope disintegrates at a constant rate called the half-life , or the time it takes for half the atoms of a sample to decay. The half-life can also be termed an atomic clock. By counting the number of half-lives and the percentages remaining of parent and daughter isotopes, scientists are able to determine what they call the absolute age of a discovery. Carbon is a specific isotope used in dating materials that were once living.
Other common isotopes used in radioactive dating are uranium, potassium, and iodine. To unlock this lesson you must be a Study. Did you know… We have over college courses that prepare you to earn credit by exam that is accepted by over 1, colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.
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What is Carbon Dating? What is Relative Dating? Absolute Time in Geology. Relative Dating with Fossils: Index Fossils as Indicators of Time.
Radioactivity : Radioactive Dating
Methods of Geological Dating: Numerical and Relative Dating. Major Eons, Eras, Periods and Epochs. Prentice Hall Earth Science: Holt McDougal Earth Science: ScienceFusion Matter and Energy: Discover how scientists determine the age of fossils, rocks, and other geologic phenomena by using the known half-lives of isotopes within each specimen, a technique known as radioactive dating. Radioactive Dating Ever wonder how scientists concluded the age of the earth to be about 4. Radioactivity Defined Elements occur naturally in the earth, and they can tell us a lot about its past.
The Half-Life Isotopes decay at a constant rate known as the half-life.
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Try it risk-free No obligation, cancel anytime. Want to learn more? Select a subject to preview related courses: Radiocarbon Dating Since all living things contain carbon, carbon is a common radioisotope used primarily to date items that were once living. Lesson Summary So, to sum this all up, radioactive dating is the process scientists use to conclude the ages of substances dating back several to many years ago by using the isotopes of elements and their half-lives.
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