00:00.00 archpodnet 1 go 1 00:06.49 alan Hello out there in archaeology podcast land this is ah Dr Alllan Garfinkel your host for the ninety ninth episode of the archaeology podcast the rock art podcast. 00:23.29 alan And we are really blessed and honored to have ah mine rat Andre who goes by Andy a biogeochemist director of the max plake institute for chemistry and mindz a review editor of the journal of science a fellow of the american association for the advancement of science and. He and his associates have published more than 500 articles and books in scientific journals and he tells me that that Wikipedia effort is probably out of date is that correct Andy. 00:54.59 Andi Yes I think it is I actually haven't looked at it myself for quite a while. 01:01.68 alan So Andy and I met when he and I did um a bit of research on the coso rock art there in the western Mojave Desert so Andy was kind enough to to spend ah quite a bit of time with us. And do some dates and we'll get to that one probably ah in the second segment but Andy I'd like you to spend a little bit of time giving people a soundb bite about your your background and your interests and how you ah. Thread the needle per se and got out to the study of dating of rock art which is quite a remarkable subject. 01:45.44 Andi Well yeah I don't quite know how far to go back. But but in fact, when I was just finishing high school I had to decide whether I was going to do one of my favorite things and that is going into Anthropology Ethnography. Or another one which is so going into chemistry and I guess eventually I decided chemistry had sort of well better career prospects and ended up going into chemistry and then um. 02:18.61 Andi Ah, since so living and working in a lab all the time really didn't satisfy me so much I ended up going into geochemistry and studied hard rocks in Norway and then eventually moved on to soft rocks to sea water to the atmosphere and um. And um, one of my field trips actually ended up in the California desert and I saw all this black stuff that was coding the rocks out there and that sort of puzzled me at the time. Well this rock varnish desert varnish stuff. Um, where does that come from how does that form. 02:56.96 Andi And that's a question that I actually first asked myself sort of in the um, ah mid 1970 s and then pretty much forgot about it until I read an article um ten or so years ago um about so the biological involvement in forming this this rock vaish. So I thought that's an interesting topic and so I started to look at the geochemistry and the biogeochemistry of rock varnish now how did I get into the anthropology archeology part of it. Well. I thought naive geochemist that I am that the archaeologists would know how old rock art is and and I was interested interested the question of so how fast does tesa varnish form. So what's the idea. Um, I go and find rock art someplace I measure the amount of varnish on there and then ask the archaeologist. How old is that rock art and then well I can calculate how fast the varnish forms it so turned out. Um. I had overestimated the the archaeologists because the first question they asked me is ah well we don't know how all that stuff is but we'd like you to tell us with all your beautiful measurements and also that's how I ended up working for well by now probably about a decade. 04:29.32 Andi On trying to figure out how to make measurements on rock art and how to actually come up with estimates for for the age of that rock art. 04:37.56 alan Now you began your studies in the Middle East did you in Saudi Arabia 04:44.73 Andi Yeah, first ah worked in in Saudi Arabia and the the great advantage there for my purposes was that there in the in the desert of Saudi Arabia you find a lot of inscriptions. So. 05:00.77 Andi People in the Middle East were pretty much the first to develop writing and they applied this writing to all sorts of things like to to mud Clay bricks and so on and develop one of the the first styles of writing there. But they also wrote on rock and they did this in the same way that other rock artists created they scraped off or picked off the rock varnish and then they had sort of light on dark inscriptions. And the nice thing is they started to do that. Well some two and a half to maybe three thousand years ago and they used different styles of writing different alphabets and the the epigraphers the people who start who study inscriptions. 05:36.89 alan Um, so. 05:53.20 Andi And writing so the epigraphers had a fairly good idea as to what styles were used when um so there is all these things called hisic and s saphaetic and data nitic and so on um, different styles of writing and um. So if I made measurements on those things actually then I could get an idea as to well knowing how old they are knowing how much new raucus varnish has formed on these on these inscriptions then I could get an idea as to how fast that barnish forms. The other nice thing about working in in Arabia is that there's been some really sharp climatic transitions. There's something called an Arabian Humid period which ended about about but five thousand years ago and during that humid period. Was enough rainfall in Arabia ah, that water was pretty much reliably available and that enabled people to hold cattle because cattle actually they need to drink basically pretty much once a day or at least every other day. And so in inscriptions that date back to the humid or rock art that dates back to the humid period. Um, you do see cattle and then about five thousand years ago the cattle disappear from the rock art and what we'll find then is the um. 07:19.53 Andi Domesticated Camel because that's a dry adapted animal and so we use these sort of transitions in the the ecology and and in human activities as well as inscriptions to give you a fairly good idea as to. 07:38.57 Andi Markers how old things are and from that you derive the rate at which the the varish accumulates and then knowing that rate you can then start to date things that don't have any identifying things like. Climate transitions or or writing you can then date things like humans that are seen in beautiful dancing scenes from the but ten thousand years ago actually ah the early holocene of pre pre neolithic figures. Down to horsemen scenes that are maybe about thousand years old um in the in the arabian desert. 08:25.32 alan Pretty amazing. Um, tell us a bit about what rock varnish is and what you've learned about the nature of how it's formed I Believe it's ah it's it's still ah somewhat of a controversial subject and I know I've. 08:33.96 Andi Um, yeah, okay. 08:41.42 alan I've read extensively about it. But what do we think we know about how this desert varnish is accumulated principally on sandstone and also on volcanic rocks I would presume although I have seen it on granted as well. 08:55.81 Andi Yeah I mean rock. Ah, ah, varnish or desert varnish some people call it a rock varnish pretty much conform on almost any surface that um, that's resistant enough to weathering to stick around for um thousands or. Tens of thousands of years and so basalt is a very good substrate. It forms nicely on basalt. It just also forms on granite and lots of granite a nices some. It doesn't like to form on carbonate rocks because they tend to dissolve too rapidly so on limestones typically you don't find it ah and people have argued a long time about how it forms so first. What is it? Well, it's a ah, visually dark blackish dark brown ah thin layer of um, a mixture of Clay minerals. 10:02.19 Andi Manganese oxides iron oxides the occasional quartz grain and the the way it forms now is that actually dust settles on a rock surface and that dust contains just like any other rock or material on the earth surface. But it's elements so including Manganese and manganese is kind of an interesting element because it can exist in many different chemical forms. There's one form which is called Manganese two and that's quite a soluble material and. This Manganese two can be oxidized to Manganese four which is very insoluble so you can think about the same way kind of as iron. You can have iron as a metal you can dissolve that iron like an acid. And then it's soluble. But if you take that iron and let it oxidize to form basically rust then it becomes very insoluble and then it coats a surface and so in a way it's akin to rust formation the um manganese gets extracted by. Solutions by a little bit of moisture that's on the on the on the rock and coats. The dust gets extracted and then it becomes oxidized and rerecipitates and so it's the as I say it's the the manganese equivalent to to iron rust. So how does it form? Well, ah. 11:34.72 Andi Dust settles on the rock then comes some humidity which gets deposited from a little bit of rain or a bit of dew and extracts the manganese it gets exposed to the air gets oxidized and then the manganese oxides that precipitate. They just bind together as a cement. Ah some of the some of the dust some of the mineral grains some of the clay minerals and form this thin layer on the rock which's about or off the odor of a human hair or the thickness of maybe. 10 times the thickness of a human hair that sort of order of magnitude and it forms a nice dark shiny coating that you can see a lot when you go out into the desert. Um, so both on boulders on the ground and also on rock outcrops vertical surfaces and that makes ah. Sort of a canvas for an artist a stone age artist who then can inscribe basically into this or into this rock barnish his writing or his his art figures. 12:46.10 alan So what I what I believe I've seen is throughout the California desert and other places throughout the great basin but mainly in California is the substratum is basalt and of course this desert varnish. Has a ah gray or blue or even black tenor to it and what happens is they they use ah some sort of a pick some sort of a courtrtz pick to penetrate the varnish to. Expose the heart rock which is the light heart rock. That's unvarnished and then disappears as the elements or the particular incisions that are produced on the canvas and. Is the basis for the art forms or the writing or the engravings that occur am I correct. 13:49.51 Andi Yes, exactly and the first this can be done in a number of different ways. It can be done by basically direct incision. So the guy just takes ah a sharp rock and starts peking away. Directly on the substrate on the surface that he wants to put the rock art onto and well I'm saying he because we assume that most of rock artists may have been men but we don't actually know that um and given the fact that there is also. Female shamans and um, um, it may well have been that and shamans have been implicated in in creation creation of rock art. So it may well be that. Um there's also female rock artists. But anyway. Our rock artist can do this by by basically the direct ah percussion direct hit directly hitting the rock surface with ah with a sharp rock chisel or ah to make more sophisticated rock art. Um, they can take 1 sharp. Chisel and another hammerstone put the chisel onto his his rock surface and then ah pound on the back of it with the hammerstone which allows much more control. Um other methods are actually which works well on sandstone are taking a chisel and. 15:14.57 Andi Basically scrape or grind off larger surfaces so there are a number of techniques that are being used to clear the the varnish off of the rocks upstrate. 15:27.13 alan Andy Let's stop there. We'll call it a call it a complete segment and in the next one I think we'll ah dive a little deeper into some of the research that you've published dating rock art and 4 different publications. 15:36.49 Andi Okay, wow. Okay, all right. 15:43.49 alan See in the Flip-flop gang.