Does Radiometric Dating Prove the Earth Is Old?
The standard scientific estimate is uranium lead dating creationism the universe is about 15 billion years old, the earth about 4. It is important to recognize from the start that there are independent procedures for obtaining each of these estimates, and that the procedures yield ranges of values uranium lead dating creationism overlap.
In the case of the universe, estimates can be obtained from astronomical methods or considerations of nuclear reactions. Astrophysicists japanese dating sim free online measure the rate at which galaxies are receding and use these measurements to compute the time needed for the universe to expand to its present size. A second, independent, astronomical method is to use standard techniques to measure some parameters of stars mass, luminosity, compositor, and surface temperaturefrom which a well-confirmed theory of the life histories of stars enables physicists to compute their.
Finally, considerations of radioactive decay make it possible to calculate the time at which certain heavy elements were formed. These techniques are somewhat similar to the radiometric methods of dating rocks, which I shad consider in a little more detail. For an excellent overview of the various ways of assigning an age to the universe, and an exposition of the radioactive decay method, see Schramm Although the clear consensus of physical techniques is that the universe is billions of years old, and although this result controverts the claims of at least some contemporary Creationists, the principal Creationist attack has been directed against the standard geological claim that the earth is about 4.
Two kinds of arguments are offered. In the first place, Creationists argue that methods of radiometric dating employ false assumptions. They continue by using special techniques of their own to assign to the earth an age of a few thousand years. Excellent and exhaustive explanations of the errors in Creationist arguments about dating methods have been given by Stephen Brushand Brent Dalrymple My aim in the following brief discussion is simply to hit the high spots.
The basic idea behind radioactive dating is very simple. If a radioactive isotope the parent element was originally present in a rock at the time of its formation, then that isotope would give rise, by radioactive decay, to decay products daughter elements. The phenomenon of radioactive decay is well understood by nuclear physicists. It is governed by the following equation: Suppose that, at the time of formation of a rock, P 0 atoms of a parent element and D 0 atoms of one of its daughters were present.
Suppose also that the rock neither gives up nor receives additional parent or daughter atoms during the ensuing years and that today atoms of the parent element and D t atoms of the daughter element are present. Then, by the assumption that parent and daughter atoms neither entered nor exited, we know that the extra daughter atoms that are now present must come from decay of the parent. So we can From equation 1 we get.
Combining 2 and 3 gives. Elementary algebra will enable us to compute t from this equation, provided that we know P tD tD 0 and l. Since constants of radioactive decay are uranium lead dating creationism to elements, experimental studies of the decay of the parent element in question provide the value of l.
P t and D t can both be calculated by measuring the amounts of parent and daughter isotopes found in the present rock. As Dalrymple points out, available techniques give us uranium lead dating creationism than the accuracy we need. But there is an apparent problem with D 0. How can we figure out the amount of the daughter element originally present? The answer is that in many cases if we choose the right element for the right rock we have excellent reasons for believing that D 0 is zero or, at least, negligibly small.
In other cases, as we shall see, we can use present rock compositions to infer the value of D 0. Obviously, there are two major assumptions involved in the use of radiometric dating. Scientists have to estimate D 0 and they have to rule out the possibility that additional quantities of the daughter element have been added since the time the rock was formed. Actually, the computation of the age would be affected if some of the daughter element originally present had been lost.
For if uranium lead dating creationism daughter element were added, then we should arrive at too large a figure for the amount of the parent element that has decayed, and thus produce too high a value for the age of the rock. Geologists are not unaware of these assumptions, and they take great pains to construct ways of cross-checking them. Consider first the uranium lead dating creationism of computing D 0. Argon is an inert gas, so that it does not occur in chemical compounds in original rocks.
In some crystalline structures it can be trapped mechanically, but for other naturally occurring minerals it can be shown that this does not occur. A second common method of radiometric dating involves the decay of uranium into lead. Here it is possible to use two decay processes, the decay of uranium into lead and the decay of uranium into lead Furthermore, the amount of lead originally present can be computed by considering another isotope of lead. Hence, by measuring the amount of lead in a uranium lead dating creationism, geologists can estimate the uranium lead dating creationism of lead originally present.
Given this value of D 0 it is then possible to use either decay process to calculate the age of the rock. If the results agree, they are said to be concordant, and geologists are usually confident that concordant ages are the true ages of the rocks under consideration. The second worry is that extra amounts of the daughter element may enter the system after the original formation of the rock, thus giving the impression that more of the parent element has undergone radioactive decay than has actually been the case.
In both the examples I have described, there are ways of checking that such intrusions have not occurred. Minerals can be tested for their capacity to absorb extra argon under experimental conditions designed to resemble their natural environment, and geologists can screen out, in this way, minerals that are liable to give erroneous results.