I was watching a television show about Australia and they got to talking about some paintings done on some rock walls by the aborigines. Then the narrator said something like, “These designs were painted 13,200 years before the birth of Christ.”
I didn’t think there were methods that could accurately date something that far back with a degree of precision great enough to determine an age to within a hundred years or so. Usually what I encounter in my reading is aproximations within thousands of years, or even tens of thousands of years with some extremely old stuff (like dinosaur bones).
So was this show BS (it was geared towards potential tourists, not science buffs)? Or have scientists found a more precise method of dating now?
A scientific exposition would doubtless include a tolerance on that number. Most popular TV shows don’t bother with that refinement. 13000 is at the extreme of carbon-14 dating so it would have a pretty wide spread of uncertainty. Incidently, the year of the birth of Christ isn’t known all that well either so the 2 at the end of your title isn’t significant either.
Considerable work has been done in developing calibrations for carbon-14 dating. These involve the use of things like Bristlecone pines where precise dates can be established back to about 8000 years by counting rings. Coral reefs, in which annual growth can also be identified are also used. These calibrations are used to take account of variations in the amount of atmospheriic carbon-14 over time.
Any encylopedia will give a good rundown on such dating methods.
I believe that dendrochronology (examining tree rings, correct me if I’ve got the wrong word) can date wooden things to the season of a particular year. I don’t know how far back they can go, but I think it’s at least a couple of millenia.
Experts have noticed that tree ring patterns over the course of a few decades (eg the period 1620-1670) are the same for different trees growing in different parts of the world. They have put together the jigsaw of ring patterns from trees whose ages overlap and worked out a pattern going back to ancient times. Apparently, any bit of wood with enough rings on it can be fitted into this long pattern and thus dated very precisely.
That should give you a good indication of how carbon-dating is used. Presumably, the paint used on the cave walls contains some sort of crushed plants or whatever, so there is carbon-14 in them. As others have noted, there is a margin of error in carbon dating, and the TV show might better have said “roughly 13,200 years.” Anyone with a scientific mind would ask, what’s the margin of error?
Of course, it’s possible that the cave artist signed his name and wrote a date on it. “Ugh-Oook drawed these pictures, July 3, 15307 BC.”
My memory wasn’t too good on the applicability of the carbon-14 dating method to long-ago ages. The method is good back to about 50000 years ago before the carbon-14 count falls so low that the background radiation begins to interfere with the measurement.
At 15000 years there is still about 16 to 17% of the original carbon-14 left. The half-life of carbon-14 is given as 5730 with a plus/minus uncertainty of 40 years. So, the 15000 year dating would have an uncertainty of plus/minus 100 years, approximately, because of the uncertainty in the half-life. To this would have to be added any measurement errors.
