Sometimes only one method is possible, reducing the confidence researchers have in the results. “They’re based on ‘it’s that old because I say so,’ a popular approach by some of my older colleagues,” says Shea, laughing, “though I find I like it myself as I get more gray hair.” Kidding aside, dating a find is crucial for understanding its significance and relation to other fossils or artifacts.
Methods fall into one of two categories: relative or absolute.
In historical geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from very young (radiocarbon dating with Radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes.
Particular isotopes are suitable for different applications due to the type of atoms present in the mineral or other material and its approximate age.
Sites I have studied include Olduvai Gorge in Tanzania to look at early human evolution, Iringa in Tanzania to estimate the evolutionary history of our own speices, Mesmaiskaya Cave in Russia where there may have been overlap of modern humans and Neanderthals, and Moendas Cave in Brazil, location of the oldest human skeletal remains in the Western Hemisphere. An exciting application here has been the study of burnt bones from South Africa.
Evidence shows that they had to be heated in a campfire.
Paleontologists still commonly use biostratigraphy to date fossils, often in combination with paleomagnetism and tephrochronology.
The good dates are confirmed using at least two different methods, ideally involving multiple independent labs for each method to cross-check results.
For example, techniques based on isotopes with half lives in the thousands of years, such as Carbon-14, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments.
One of the most widely used and well-known absolute dating techniques is carbon-14 (or radiocarbon) dating, which is used to date organic remains.
Our Alaska work continues and we concluded the 2014-15 NSF/Keck field project with six students in eastern Prince William Sound in southern Alaska.
This project was focuses on understanding the Paleocene and Eocene Orca Group that was derived from the uplift and erosion of the Coast Range in British Columbia. Thompson, Encyclopedia of Earth Sciences Series 2015, Springer, Dordrecht, Netherlands.
Absolute dating provides a numerical age or range in contrast with relative dating which places events in order without any measure of the age between events.