Science

We might be overestimating the age of ancient rocks

We might be overestimating the...
An overlooked variable may be causing scientists to date rock samples as older than they really are
An overlooked variable may be causing scientists to date rock samples as older than they really are
View 1 Image
An overlooked variable may be causing scientists to date rock samples as older than they really are
1/1
An overlooked variable may be causing scientists to date rock samples as older than they really are

Much of our understanding of the ancient history of our planet comes from radioisotope dating, a process where scientists calculate the amount of certain isotopes in a geological sample to determine how old it is. But according to new research out of North Carolina State University, a flaw in this widely-used technique may be skewing the results so samples seem much older than they really are.

Radioisotope dating hinges on the fact that over time, certain radioactive isotopes will decay to form other isotopes: For example, rubidium-87 decays into strontium-87, with a half-life of 48.8 billion years, but strontium-87 is stable so it doesn't decay. To estimate when a sample of rock formed, scientists first calculate the concentration of both rubidium-87 and strontium-87 in the sample, and then compare those to the concentration of strontium-86, as a kind of baseline.

By calculating the ratios of rubidium-87 to strontium-86, and strontium-86 to strontium-87, a graph called an isochron is created, which scientists can then use to determine the age of a sample. The process works best on igneous rocks, and has been used to study Earthly and lunar formations for decades. But, as the NC State study suggests, that final figure might not be taking other variables into account.

For one, the atoms of different elements will diffuse through a material at different rates due to a process known as differential mass diffusion. In this case, strontium-86 atoms are smaller than strontium-87 or rubidium, meaning they will spread through surrounding rock faster, and that differential may be influenced further by the properties of the sample itself.

"It's a slow process, but not necessarily a negligible one when you're talking about geological time scales," says Robert Hayes, author of the study. "The rate of diffusion will vary, based on the sample – what type of rock it is, the number of cracks and amount of surface area, and so on."

The process as it's currently applied, Hayes says, is likely to overestimate the age of samples, and considering scientists have been using it for decades, our understanding of Earth's ancient timeline could be worryingly inaccurate. That said, Hayes does point out that the issue doesn't affect carbon dating, a separate process that's used to date younger samples on a scale of thousands of years rather than millions or billions.

"There's not a simple equation that can be applied to every circumstance," says Hayes. "Researchers will need to evaluate samples individually, then apply the relevant physics accordingly. It's a pain in the neck, but it will make our estimates significantly more accurate. If we don't account for differential mass diffusion, we really have no idea how accurate a radioisotope date actually is."

The research is published in the journal Nuclear Technology.

Source: North Carolina State University

16 comments
Bob
I have always wondered if the different isotopes were simply deposited at the same time and had very little to do with true age.
JimFox
Y.E. Creationists will be gloating!
Dan Werner
So, is it off by millions of years or billions of years or are they at least in the universal ballpark.
Lardo
I made this same argument (other, perhaps even unknown, variables) to my high school science teacher... way back in 1972. He told me I was an idiot, and that the science of radioisotope dating was settled.
Oops.
Primecordial
Hmmmm....if the facts don't fit the theory, change the facts.
Dan Lewis
Mistakes aside, the age of rocks are STILL MUCH OLDER than the outrageous 12 Thousands years maximum posited by the deluded 'young earth' silly people.
Religion comforts...and cripples. History is quite clear on the matter.
Fretting Freddy the Ferret pressing the Fret
Aha! Take that Science! The Earth is 5000 years old! /notseriousatall
Peter Debney
Radioisotope dating is not the only option, and any scientist exercising due diligence will use a number of methods. For example Potassium-Argon dating does not rely on assumptions of the initial distribution of the two elements as any Argon present in the molten rocks will bubble out leaving just Potassium present. Any Argon subsequently found to be present will be there due to Potassium decaying into Argon. Thus from our knowledge of the half-life of Potassium and the ratio between the two can give us a good estimate of the time since the rock crystallised.
habakak
'...our understanding of Earth's ancient timeline could be worryingly inaccurate....'. No surprise here. I am sure the earth is many millions of years old, possibly hundreds of millions. Or even billions. I am not sure. But I do know that we most likely are wrong by a pretty wide margin. It's just a shame I won't be around in 200 years or when we figure it out. So that I can laugh at 2017-man for his misunderstandings!
John Gochnauer
*yawn* It's not like I believed this "millions of years" foolishness to begin with.