These deposits, which cannot be older than the cave art itself when they overlie the cave paintings, provide a minimum age for the artwork.
The age of the calcite was determined by a technique known as uranium-thorium (U-Th) dating, which is less destructive than radiocarbon dating and only requires a few milligrams of sample material.
The researchers’ results are published in the 15 June issue of the journal is excited to be publishing this paper because it both develops an approach for dating cave art and provides a rich series of dates on art in numerous caves,” said Brooks Hanson, the journal’s deputy editor for the physical sciences.
Cave paintings are among some of the earliest examples of art and human symbolic behavior, but inconsistencies produced by radiocarbon dating techniques have prevented archaeologists from understanding how different styles and practices developed.
To know for sure, researchers will have to keep searching for even older cave art.
The differing chemistries and half-lives of these nuclides (with timescales ranging from seconds to billions of years) make them exceptionally useful chronometers for variety of natural processes and materials Perhaps the most important and commonly used isotopes are Ra, the first three of which are commonly used to date the formation of carbonate minerals and skeletal materials (e.g., corals and cave deposits) and the full suite of which are used to date volcanic materials, such as lavas and the crystals they contain.
Because these isotopes are related to each other by a radioactive decay chain, a material left chemically untouched for a long period of time (a “closed system”) exhibits a special condition called secular equilibrium, wherein the activity of each isotope in the chain is the same (activity is defined as the numbers of decays per unit time, which is equal to the number of atoms of that element times its decay constant).
Materials that can be dated using U-series techniques are those that either (A) form by a process that causes disequilibrium, which results when the isotopes in the decay chain become separated (“fractionated”) in some way, or that (B) form by a process that records an existing disequilibrium in the material they form from.
For instance, when crystals form in a magma, Th, U and Ra in the magma enter the different materials in different proportions, producing radioactive disequilibrium.
Over time, this signature goes away, eventually relaxing to a condition wherein the disequilibria are no longer detectable.