Radiometric dating is incredible.
Above you can see a radioactive isotope of lead 212 decaying in a chain down to lead 208. This process of radioactive decay is, generally, predictable, and therefore can be used to figure out how old certain things are.
The basic idea is pretty simple:
- Almost all matter on Earth has trace amounts of radioactive isotopes in it.
- Each radioactive isotope breaks down, or "decays", into other particles at a predictable rate. This rate is called the "half-life" of the isotope.
- By measuring the amount of certain radioactive isotopes, and their decay byproducts, in an old object, and comparing that measurement to a known environmental sample, scientists can calculate the age of a given object with a startling degree of accuracy.
The devil, of course, is in the details. There are a great many things that need to happen to make sure that the dating is accurate. For instance you need to make sure that you correctly measure a series of environmental or geologic samples in order to get a baseline for comparison. What you're trying to get with this sample is a measurement of the radioactive elements present at, roughly, the creation of the material. This can be difficult, because sometimes material can be contaminated with radioactive material long after its creation. There are a variety of ways scientists use to confirm that they are getting an uncontaminated measurement, including sampling multiple places in a given area.
Despite the difficulty of an accurate dating, when carried out correctly, radiometric dating can un-cover not only the age of an object, but details far beyond what you might initially imagine.
The amazing granularity of modern archaeology.
Archaeologists are always striving to better understand how human civilizations developed in centuries and millennia past. Often this search for the past takes on fairly obvious forms: digging up old ruins or finding old bones.
But in the age of DNA and radiometric dating, the search for history has become surprisingly granular. By measuring radioactive carbon isotopes in a piece of pottery, you can date it to within a couple of centuries. By swabbing the inside of the vessel, you might be able to perform a DNA analysis and find out whether it was used to hold water, wine or milk.
These are all super impressive feats of archaeology - but researchers have recently taken this eye for detail to a whole new extreme..
Using radiometric dating to identify the lives of cows from over 2000 years ago.
Here's what the scientists in this study did:
- They exhumed the bones of 26 long, long dead cattle.
- They took their teeth, measured the amount of enamel left, and then painstakingly measured the amount of strontium present in them.
- Then they took a wide variety of baseline measurements from local geological and foliage samples in several different areas surrounding a lake where an ancient town used to exist.
- Finally, they compared the radiometric information from the cattle samples to the baseline radiometric information from the various ecological samples.
The results are an astonishingly detailed map of herding practices for this small, ancient European town.
The scientists measured the ratio of two different forms of strontium isotope in the cattle teeth and found a ratio range of 0.7075 to 0.7143. Then they compared these results to the baseline results from several local eco-systems. The results of the baseline tests were as follows:
- The area directly around the ancient town was the surest baseline measurement with a range of 0.7083–0.7091
- The area farther away, in the forested areas, had a modern vegetative range of strontium greater than the town.
- The alpine area above the forest line had the highest modern vegetative range of strontium of them all.
Comparing the baseline and modern radiometric ranges of the farther away areas to the measurements in the cattle teeth, a pattern emerges!
- 8 of the cattle fell within the baseline range - indicating a more sedentary life living in and around the town itself.
- 5 of the cattle fell within the range of the nearby forested areas - indicating a life spent foraging for food in and around the local forests.
- And 12 of the cattle fell within the highest range of the alpine area above the forest line, indicating herding at a substantial distance from town, and cattle sustenance derived from the grasses of the alpine areas.
A more complete picture
When I told my wife about this study, she was intrigued, but asked "but, why do they care?" I can't blame her for that - it's all pretty distant from our present, crazy reality. But insofar as archaeology is considered a worthwhile endeavor in the first place, this kind of analysis allows for a degree of understanding which has previously been impossible. Plus, not only does it have the immediate effect of clarifying ancient human herding practices - but the underlying principles involved can doubtless be applied to any number of ancient behaviors. The results of future studies could clarify daily life with far more granularity than anyone has been able to before.
Information Sources:
[1]Gerling C, Doppler T, Heyd V, Knipper C, Kuhn T, et al. (2017) High-resolution isotopic evidence of specialised cattle herding in the European Neolithic. PLOS ONE 12(7): e0180164
[2][https://en.wikipedia.org/wiki/Radiometric_dating#Radioactive_decay]
Picture Source:
[1]By Eugene Alvin Villar (seav) (Own work) CC BY-SA 3.0 , via Wikimedia Commons
[2]By Keith Weller%2C U.S. Department of Agriculture Public domain, via Wikimedia Commons
[3]Gerling C, Doppler T, Heyd V, Knipper C, Kuhn T, et al. (2017) High-resolution isotopic evidence of specialised cattle herding in the European Neolithic. PLOS ONE 12(7): e0180164