If you only read the news headlines and the stories that go with them, you would be led to believe that scientists have found the oldest cave paintings in the world in Spain. But you would be misled if you believe the articles.
The articles are filled with speculations about who painted them: neanderthals or “modern” man. There is debate over whether neanderthals were more sophisticated than people tend to believe. Scientists who spend their lives and millions of dollars in grant money debate these issues among themselves.
But what there is absolutely no doubt or debate about is the age of these paintings:
“New tests show that crude Spanish cave paintings of a red sphere and handprints are the oldest in the world, so ancient they may not have been by modern man.”
They are always absolutely certain about their age — until new evidence gives them a date that is more certain than the last one.
As it turns out, scientists think these cave paintings are older than they previously thought: 40,800 years old instead of approximately 25,000 years. From the Yahoo News article:
“Testing the coating of paintings in 11 Spanish caves, researchers found that one is at least 40,800 years old, which is at least 15,000 years older than previously thought.”
So why the big change?
The researchers used a different radioactive dating method this time: Uranium-Thorium instead of Carbon-14.
Over time, uranium-234 decays into thorium-230. This is the basis for the dating method.
But what do scientists actually know?
They know the ratio of the two elements present today in a sample of material. They know with reasonable accuracy how fast uranium-234 decays into thorium-230.
WHAT THEY DON’T KNOW, AND WHAT THEY AREN’T TELLING YOU THEY DON’T KNOW
But what they don’t know are the initial amounts of the two elements in the sample. So they have to guess.
They make assumptions about the initial amounts of the two elements in the samples. They assume the samples were never contaminated. This is questionable since the samples are usually out in the “open”. The samples are assumed to have been in the “open” for millions of years.
They also assume that the presence of decay products such as thorium-230 are related to the material that it decayed from.
What if the process that created the materials in the first place put those elements there at the same time? What if the initial amount of thorium-230 in the sample was not zero? How do we know the initial amount?
In order to apply these methods, the scientists have to assume that the materials are already very old. How old do they have to be at a minimum?
A BRIEF LOOK AT ONE OF THE ACTUAL ASSUMPTIONS MADE
From one of the actual reports, here are the assumptions made:
“Ages are corrected for detritus by using an assumed 232Th/238U activity of 1.250 ± 0.625 and 230Th/238U and 234U/238U at equilibrium, except age marked with an asterisk, which is corrected by using measured values on insoluble residue 230Th/232Th = 0.8561 ± 0.0039, and age marked with a dagger, which is corrected by using measured values on insoluble residue 230Th/232Th = 0.9390 ± 0.0077.”
What does it take for element isotope ratios to be in “equilibrium”? Let’s look just at the 234U/238U equilibrium assumption.
From Wikipedia, “Assuming the initial concentration of radionuclide B is zero [234U], full equilibrium usually takes several half-lives of radionuclide B [234U] to establish.”
From an EPA website: When the half-life of the original element (uranium-238) is much longer than the decay product (uranium-234) “Within about 7 half lives of the decay product [uranium-234]…the decay product decays at the same rate it is produced–a state called ‘secular equilibrium.'”
The half-life of uranium-238 is 4.468 billion years. The half life of uranium-234 is 245,000 years. In this case, the half life of the original element (u238) is much longer than its decay product (u234).
The two elements, therefore, reach equilibrium after 7 half-lives of uranium-234.
7 half-lives x 245,000 years per half-life = 1.7 million years.
The scientists are assuming that the earth is at least 1.7 million years old in order to apply this method.
For these cave art paintings to be 40,000 years old, the earth must be at least 1.7 million years old.
In order to solve the equations that produce “ages,” uranium-234 and uranium-238 have to be in equilibrium.
They would derive different results if they assumed the earth was a different age. They may determine that the dating methods they are trying to use are inadequate.
The results are based upon the assumptions. If the assumptions are wrong, the results are wrong.
How do we know which is right or wrong: millions (or billions) of years or 6,000 years? The answer is that one must have faith: faith in the ability of man’s fallen reason to judge right and wrong, or faith in the infallibility of God’s eternal Word that tells us what is right and wrong and faith in our God-given reason to operate within those bounds (science).
Intellectually honest scientists would admit that their results are highly speculative. However, doing so may lead to their grant money drying up.
For a brief overview of dating methods and their assumptions, click here.