______________________________________________________________ ____________________________________________________________________ ____________________________________________________________________________________________ _______________________________________________________________ Relative Ages of Rocks: WIki Books (Wiki Books: A project hosted by the Wikimedia Foundation for the creation of free content textbooks) Willard Libby and Radiocarbon Dating.American Chemical Society A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012), from the National Research Council of the National Academies. Radioactive decay lifetimes and isotopic content in rocks provide a way of dating rock formations and thereby fixing the scale of geological time.College Board Standards for College Success: Science ES.3 Earth’s History: Relative and Absolute dating.Students understand that various dating methods — relative and absolute — have been used to determine the age of Earth. Between Earth Science and Other Disciplines: Evidence of Common Ancestry and Divergence (LS.1.1); Living Systems and the Physical Environment (LS.3.1); Nuclear Chemistry (C.1.6); Nuclear Interactions and the Conservation of Mass–Energy (P.2.3) Benchmarks: American Association for the Advancement of Science.Knowledge of radioactivity helps them understand how rocks can be dated, which helps them appreciate the scale of geologic time…Scientific evidence indicates that some rock layers are several billion years old.is a technique used by scientists to learn the ages of biological specimens – for example, wooden archaeological artifacts or ancient human remains – from the distant past. To understand radiocarbon dating, you first have to understand the word Although an element’s number of protons cannot change, the number of neutrons can vary slightly in each atom.It can be used on objects as old as about 62,000 years. Atoms of the same element that have different numbers of neutrons are called isotopes. Most carbon on Earth exists as the very stable isotope carbon-12, with a very small amount as carbon-13.
Radiocarbon dating uses isotopes of the element carbon. Cosmic rays – high-energy particles from beyond the solar system – bombard Earth’s upper atmosphere continually, in the process creating the unstable carbon-14. Because it’s unstable, carbon-14 will eventually decay back to carbon-12 isotopes.Because the cosmic ray bombardment is fairly constant, there’s a near-constant level of carbon-14 to carbon-12 ratio in Earth’s atmosphere.Organisms at the base of the food chain that photosynthesize – for example, plants and algae – use the carbon in Earth’s atmosphere.They have the same ratio of carbon-14 to carbon-12 as the atmosphere, and this same ratio is then carried up the food chain all the way to apex predators, like sharks.But when gas exchange is stopped, be it in a particular part of the body like in deposits in bones and teeth, or when the entire organism dies, the ratio of carbon-14 to carbon-12 begins to decrease.
The unstable carbon-14 gradually decays to carbon-12 at a steady rate. Scientists measure the ratio of carbon isotopes to be able to estimate how far back in time a biological sample was active or alive.