I was watching a show on the History channel and they showed these large stones in Nevada, the stones had symbols carved directly into the rock.
They then state “these carvings have been dated to more than 10,000 years ago”
I understand how cave paintings can be dated based on the substance added to the rock. In this case however, nothing is being added.
Dating is a complex question and conclusions are drawn from an assessment of a whole load of data relating to the place and the surroundings.
Did they say “carbon dated”, or just “dated”?
*Radiocarbon testing dated the carbonate layer underlying the petroglyphs to roughly 14,800 years ago.
Geochemical data, sediment and rock samples from adjacent Pyramid Lake show they were exposed to air from 13,200 to 14,800 years ago and again from 10,500 to 11,300 years ago.
‘Whether they turn out to be as old as 14,800 years ago or as recent as 10,500 years ago, they are still the oldest petroglyphs that have been dated in North America,’ said Benson, a national research scientist emeritus for the U.S. Geological Survey and curator of anthropology at the University of Colorado Natural History Museum in Boulder.
*
Geochemical carbonates can form on stone surfaces in some conditions. A rock engraving may overlie the carbonate or cut through. Having carbon content C14 dating of the carbonate is a possibility.
In the first case the date of the carbonate provides a terminus post quem [date after which the art was done], while in the second case its a terminus ante quem [date before which]. Exactly how long the art was executed before or after the carbonate is another question. It could be days or centuries.
C14 dates represent a probability range and it is common practice to use the mean date plus or minus 2 standard deviations to reasonably represent the likely possible date range.
Oops - if the engraving is overlain by the carbonate, then that provides the terminus ante quem.
Didn’t see my error back there.
yep, and they fit it in with knowledge of the local geography, climate ,etc
to be sure that there wasn’t some other event that disturbs the dating technique.
They didnt have to date the carbonate that was laid over the top, they just had to determine when the lake level was high enough to lay the carbonate on the carvings. Whether they get that directly from the carbonate or from other techniques.
(eg dating wood in the layers of sediment around the place… ) … they do as much as they can to be sure that they aren’t missing something.
I’ve got books on Southwestern Rock Art that devote entire chapters to the dating of carvings. In short, you’re right that you can’t carbon date something with no carbon in it. As others have pointed out, “these carvings have been dated to more than 10,000 years ago.” doesn’t say they were carbon dated. Even more cynically, I’ll point out that the statement doesn’t say they were correctly dated, either.
Some dating methods:
1.) Rock paintings , or carvings with painted parts may contain carbon datable pigments or binders
2.) Nearby campsites may have artifacts that are datable. It’s still a question if the site and the carving are related.
3.) Other items (like a tree growing through the carving) provide datable items after the carving
4.) geological events (like the carvings were buried by a datable rockslide or covered in a datable flood
5.) The subject matter itself may be datable (like it contains a man riding a horse. Or an automobile – yes, these really occur. Or someone claims the carving represents an astronomical event, like a nova.)
6.) Guessing.