![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
![]() |
. | ![]() |
. |
![]() by Staff Writers Raleigh NC (SPX) Feb 01, 2017
An oversight in a radioisotope dating technique used to date everything from meteorites to geologic samples means that scientists have likely overestimated the age of many samples, according to new research from North Carolina State University. To conduct radioisotope dating, scientists evaluate the concentration of isotopes in a material. The number of protons in an atom determines which element it is, while the number of neutrons determines which isotope it is. For example, strontium-86 has 38 protons and 48 neutrons, whereas strontium-87 has 38 protons and 49 neutrons. Radioactive elements, such as rubidium-87 (but not strontium-86 or strontium-87), decay over time. By evaluating the concentrations of all of these isotopes in a rock sample, scientists can determine what its original make-up of strontium and rubidium were. Then, by assessing the isotope concentrations of rubidium and strontium, scientists can back-calculate to determine when the rock was formed. The three isotopes mentioned can be used for dating rock formations and meteorites; the method typically works best on igneous rocks. But it's not quite that straight-forward. The data from radioisotope analysis tends to be somewhat scattered. So, researchers "normalize" the data by making a ratio with strontium-86, which is stable - meaning it doesn't decay over time. Dividing the isotope concentrations of all the forms of strontium and rubidium by the isotope concentration of strontium-86 generates something called the "isochron." The isochron is then plugged into a model, which uses it to turn the overall radioisotope data into a clear, linear function. This function is able to tell researchers how old a sample is. Or it's supposed to. But there's a wrinkle in the process that has been overlooked. The ratios of strontium-86 to rubidium and strontium-87 are thought to only be influenced by the radioactive decay of the rubidium-87 into strontium-87. The current model of radioisotope dating is based on that idea. But that model doesn't account for differential mass diffusion - the tendency of different atoms to diffuse though a material at different rates. And atoms of strontium-86 can diffuse more readily than atoms of strontium-87 or rubidium, simply because atoms of strontium-86 are smaller. "It's a slow process, but not necessarily a negligible one when you're talking about geological time scales," says Robert Hayes, an associate professor of nuclear engineering at NC State and author of a paper describing the work. "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," Hayes says. "So, there's not a simple equation that can be applied to every circumstance. 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," Hayes says. "If we don't account for differential mass diffusion, we really have no idea how accurate a radioisotope date actually is. It's worth noting that the issues raised here do not apply to carbon dating, which does not utilize isotopic ratios." Research paper: "Some mathematical and geophysical considerations in radioisotope dating applications"
![]() ![]()
Related Links North Carolina State University Explore The Early Earth at TerraDaily.com
|
|
The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us. |