MadSci Network: Evolution

Re: How do scientists date fossils so old, though the Earth is only 12,000?

Date: Mon Nov 29 11:27:23 1999
Posted By: David Kopaska-Merkel, Staff Hydrogeology Division, Geological Survey of Alabama
Area of science: Evolution
ID: 939784190.Ev


I found your question a little confusing, because the "subject" question 
suggests that you think there is some scientific evidence that the Earth is 
only 12,000 years old (there is not), yet the body of your question 
suggests that you do not hold this belief. I am going to answer by assuming 
that the question body was what you really meant to ask, and that the 
subject line was not.

Carbon-14 radiometric dating is actually usable, with decreasing precision, 
to ages greater than 70,000 years. However, it is true that you cannot use 
radiocarbon dating to measure the age of things that are millions of years 
old. Fortunately, there are many radioactive isotopes, all of which have 
been shown by physicists to decay at constant rates, and some of these 
isotopes have half lives much longer than that of carbon 14. Radiometric 
dating of objects millions of years old depends on use of other isotopes, 
such as those of uranium and argon. 

Of course, radiometric dating is not the only scientific method of dating 
ancient objects. Many geological methods provide relative dates, and these 
can be combined with radiometric dates to absolutely date things that do 
not themselves provide radiometric dates. Some dates are more precise than 
others, and any date given for an ancient object must include the 
confidence interval. For instance, 13.5 million plus or minus 350,000 years 
means there is a high probability that the age is between 13,150,000 and 
13,850,000 years. The confidence interval is usually either + or - one 
standard deviation (about 67%) or 90%, or 95%, and in scientific 
publications you are always told exactly what is meant. If you want to 
learn more about methods of dating other than radiometric dating, then I 
suggest you consult a textbook on physical geology, historical geology, or 
stratigraphy. Some of these should be understandable even if you don't have 
any geologic training. A good physical geology textbook is by Press and 
Siever, and the 1974 edition was called Earth (I think the latest edition 
has a slightly different name). 

The theory of evolution is a scientific theory, which means it has been 
rigorously tested by many people trying to show scientifically that it is 
not valid. No one has ever been able to provide any scientific evidence 
falsifying the theory of evolution, which is probably the most thoroughly 
supported scientific theory there is, except the theory of gravitation! The 
theory of evolution makes reliable predictions about changes in biological 
systems over time, which is what it is supposed to do. It has nothing to do 
with origins. 

Creation is a religious concept. It is not supposed to be tested 
scientifically. It is supposed to be accepted on faith (or not, as one's 
religion dictates). It has everything to do with origins. I consider 
religion a personal matter. However, I would be happy to further discuss 
the science of geology with you.

If you want to learn more about the creation-evolution controversy, then I 
suggest you visit this web site:

It is the home page of the National Center for Science Education. They 
particularly concern themselves with the nature of science, the nature of 
religion, and the relationship between the two.

I hope I have helped you with your questions.

David Kopaska-Merkel
Geological Survey of Alabama
PO Box 869999
Tuscaloosa AL 35486-6999
(205) 349-2852
FAX (205) 349-2861
web site

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