The Editors of Encyclopaedia Britannica. Learn More in these related Britannica articles: This is possible in potassium-argon K-Ar dating, for example, because most minerals do not take argon into their structures initially. In rubidium-strontium dating, micas exclude strontium when they form but accept much rubidium. In uranium-lead U-Pb dating of zircon, the zircon is found to exclude initial lead…. The radioactive decay scheme involving the breakdown of potassium of mass 40 40 K to argon gas of mass 40 40 Ar formed the basis of the first widely used isotopic dating method.
Since radiogenic argon was first detected in by the American geophysicist…. Potassium—argon dating has made it possible to establish that the earliest remains of man and his artifacts in East Africa go back at least 2,, years, and probably further. Potassium-argon dating , for instance, can provide the age of a specimen by clocking the rate at which radioactive isotopes of these elements have decayed.
When radiometric methods cannot be applied, investigators may still ascribe a relative age to a fossil by relating it to the…. More About Potassium-argon dating 5 references found in Britannica articles Assorted References major reference In dating: Analysis of separated minerals In dating: Potassium—argon methods age determination of tektites In tektite: Chemistry and petrography of tektites archaeology In archaeology: Dating Homo erectus In Homo erectus: Help us improve this article! Contact our editors with your feedback.
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Internet URLs are the best. Thank You for Your Contribution! The areas of science, which are the most successful, which the public notices, are the amazing discoveries in medicine, biology, space exploration, and the like. These are the areas that deal with the here and now.
If an experiment is conducted and the information needed to answer the problem is not forthcoming, then another experiment can be designed to answer the problem. The process can continue until some answer to the problem is understood. The problem is only limited by money, ingenuity, and the technical difficulties that have to be surmounted.
In addition to the above limitations of science, historical science is limited by the fragmentary nature of the artifacts it is able to find. In effect, the accuracy of ideas is limited by the assumptions chosen by the researchers. K-Ar dating is not based on irrefutable data alone. It has as its basis of understanding, various assumptions which concern the conditions of the Earth for hundreds of millions of years.
These assumptions were originated within an atmosphere of long age preexisting ideas.
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Scientists almost never look for indicators in nature that might speak of a very young age for the world's history. Most scientists do not believe that the short chronology of the Bible has any validity at all and most would consider it counterproductive to pursue such a course of investigation. If in fact such an answer were found, it would be quickly dismissed.
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It would be assumed that there was something wrong with the idea or the data, and a new scenario would be sought. Some papers give evidence of presenting filtered data. What is meant by filtered data, is that they only present the data that agrees with evolutionary thinking. The other data is eliminated. Potassium-argon dating and the Cenozoic mammalian chronology of North America.
Am J Sci ; This paper is now considered to be a classic paper. Yet they use biotite in an uncritical manor in other areas where the dates they obtained matched their expectations. On Page , we can also note: Thus, of some 65 samples collected by M. Skinner, only 10 could be used. Sometimes the whole rock basalt date is reported, but sometimes only a mineral fraction is reported from the basalt, like biotite or sanidine.
Why is it that one type of date is used one time and not at another time, is not discussed in the paper. As Paul Giem notes: Thus one could pick the dates that fit one's expectations and create a very impressive list of dates with close agreement without there being more than a general correlation of most dates with one's expectations. It should be remembered that these researchers are not being dishonest in their actions.
They think of the long age scenario of evolution as being fact. They do not believe that there is any alternative way to look at history. So when the data does not come out right, it is only natural that they assume that there is something wrong with the dates that do not fit the long age viewpoint.
However, when they turn around and say that the data supports the evolutionary viewpoint and not the Creationary viewpoint. This is not right! The data does not support long ages. So, many people try to say something like: But this is not true either, the weight of evidence does not prove anything. We do not have an issue of weight of evidence. Rather, what we have is weight of interpretation! This controversy is not over data. The data can go either way. Very intelligent people believe in the long history of the earth and they have good data to support them.
There is no question about it.
However, I look at that same data and I come to very different conclusions. This process is legitimate! There is such a thing as multiple interpretation to the data base. There is no proof for either position. On this web page I want to discuss a possible scenario that would allow K-Ar dates to indicate a short age chronology. Such a discussion might never be allowed in normal scientific circles because of the assumptions they choose to believe as being true.
There is such a strong consensus of opinion on K-Ar dating and other similar topics that deal with the history of the Earth that alternative viewpoints are probably viewed as being counterproductive. Before we start, lets look at the specific K-Ar dating assumptions. The rate of decay half-life , and the branching ratio, of K have not changed. The material in question lost all its argon at an identifiable time, the reset time.
No argon has been lost since the time the rock was reset, or set to zero. No potassium has been gained or lost since the reset time, except by decay. The ratio of K to total K is constant. The total K, Ar, and Ar in the material in question can all be measured accurately. The seventh assumption is one that scientists are doing their best to fulfill. We should also be able to safely make this assumption. The sixth assumption is also fairly secure.
When the concentrations of the various K isotopes are measured, the results are always the same. The fifth assumption is fairly safe.
There are some cases where K has been gained or lost; However, the mineral itself has been noticeably altered. The fourth assumption is probably satisfied for most samples. However, this is an assumption that could be challenged. If the rock was heated in the presence of Argon from the earth's mantle, or perhaps in some primordial Argon which might have had a higher concentration of Ar 36; we might have problems making this assumption.
According to most texts on Potassium-Argon dating, the third assumption is fairly commonly violated. Metamorphism, weathering, and reheating are some of the processes that are mentioned to cause a loss of Argon in the crystal of a rock. Most sedimentary rocks are thought to lose Argon because the crystal structure leaks Argon. A loss of Argon would cause the rock to date younger than it should according to evolutionary thought.
This is probably the assumption that scientists make when they choose to present filtered data in a scientific paper. They see the young dates as those samples that have lost Argon. It is an assumption that they probably view as having no alternatives, yet if this same issue was ever pursued, it might uncover other possibilities suggesting a short age time scenario.