When you need a skull, where do you go?
August 8, 2012 7:46 PM   Subscribe

How do archaeologists know where to dig?

Today I read this BBC article about fossil evidence supporting the notion that multiple species of human co-existed millions of years ago.

How do archaeologists figure out where to start digging? Especially for sites that do not have locations in written record? The mind boggles at the probability of randomly hitting paydirt.
posted by burnfirewalls to Science & Nature (20 answers total) 16 users marked this as a favorite
Paleontologists (who are the ones finding fossil material, not archaeologists) are looking for particular sediments of particular ages in places where those sediments are exposed. Fossils are generally found in sedimentary rock, which is formed when layers of sediment (especially from erosion and water transport) are deposited on top of eachother. If this happens to include a bit of bone, that gets incorporated into the sedimentary rock. Usually, sedimentary rock is capped above and below by volcanic rock, but there are places where the volcanic rock erodes away and you can see exposed sedimentary rock. That's your best bet for finding fossils.

People have been doing paleontology in Northern Kenya and other parts of the Rift Valley since the early 1900s, and that whole area is very well understood in terms of what sediments are exposed and what ages these sediments probably are. Turkana, where they're finding these fossils, is a particularly rich fossil deposit because it's had constant water deposition of sediments and it's always been a relatively dry environment so things stuck around instead of totally decomposing as they might have in a rainforest. Aerial photography has been very important for finding exposed sediments because, when you're looking down at an area mostly covered by basalts, sedimentary rock looks very different and is very obvious. You can do this looking around googleearth, too - type in Lokichar, Kenya and look around at the different colorations of rock that are exposed. Some of those will have fossils, many of them will not.

I was a field assistant on a paleontology project in West Turkana looking at deposits much older than where they're finding human ancestors - we were trying to find some early monkeys and carnivores in Africa about 23 million years ago (right about the time Africa bumped into Europe). My advisor knew where to start looking because he'd found fossils of the right age and type in previous years, but there were days when we drove around the general vicinity looking for new places with exposed sediment. One day, we ended up in the Miocene (only about 10-8 million years) by accident, and started finding totally weird fossils, like pig teeth. So we moved on.

On days when we knew approximately where fossils were, but just had to find them, we literally just walked across the landscape looking for sediment exposures and bits of fossil material in the surface. I wasn't very good at this sort of prospecting, but I found some exciting things (in the Miocene, I found a teeny tiny rodent jaw!), like some primate canines and some crazy meat eating mammals that were in Africa before carnivores.
posted by ChuraChura at 8:03 PM on August 8, 2012 [67 favorites]

I'm not an expert in this, but I believe the folks involved in this dig are anthropologists -- involved in the study of the origins of human life, including pre-Homo Sapiens human ancestors -- not archaeologists -- involved in the study of human cultures, which are tied exclusively to Homo Sapiens.

To answer the question you asked: Archaeologists often know where to dig because other human activity unearths signs of past human activity. Construction of a skyscraper reveals bones that turn out to be a cemetery. Construction of a highway reveals an American Indian village. Other times, they find other clues in the environment. This mound does not seem like a naturally occurring hill -- I wonder what I'll find if I dig into it? When we fly over this portion of the Amazon rain forest, patterns emerge in the landscape that suggest past human activity -- let's explore where the patterns converge. Sometimes they don't even need a physical clue. A place has been continually inhabited for thousands of years, and we want to know more about long-ago residents. The historical record tells us that interesting things happened here once, so now we want to explore.

Anthropologists, I'm not so sure, though I suspect the proximity of past discoveries and the guidance of local people and their legends may play a role.
posted by croutonsupafreak at 8:04 PM on August 8, 2012

It's true that the people doing paleontology specifically to find direct human ancestors are anthropologists/paleontologists - usually, paleoanthropologists. But they're often also experts, or at least quite knowledgeable, on other fossil material they're finding - usually animals, but sometimes fossilized plants and soils, too.
posted by ChuraChura at 8:09 PM on August 8, 2012

ChuraChura gave a really good answer about looking for fossils (although I'd quibble that these are paleoarchaeologists, not paleontologists, I'm applying to grad schools right now to study human origins and I would most definitely train under archaeologists). As for finding less ancient stuff, outreach is a huge part of it. Many times the locals know where the archaeological sites are, you can often see evidence on the surface like pot sherds or the remains of stone tool making.

You also might find a site during survey work, which is good old fashioned boots on the ground. People walk, say, 10m apart and keep their eyes on the ground for anything that might be an artifact.

There are other, fancy methods like ground-penetrating radar or magnetometers but really the majority of sites are found by word of mouth and getting out there and walking.
posted by TungstenChef at 8:12 PM on August 8, 2012 [1 favorite]

Your user name, "burnfirewalls," actually illustrates some helpful other ways of identifying archaeological sites: evidence of burning in the soil layers, evidence of walls either above ground, visible through various technologies, cropmarks, etc. England has produced some really stunning examples of archaeological sites visible from the air, including amphitheaters in fields and temples. If you look in the fields near Oxford, England, you can see remnants of Bronze Age sites and Civil War encampments through Google Earth. English Heritage also has some great pictures of sites. Aerial surveys (and LiDAR) also help identify plausible sites based on key characteristics, like straight lines, orientation of sites, evidence of roads or tracks, fields, and other things that may indicate past human habitation. In other cases, like the great Tells of the Near East, sites are literally built up one by one, creating mounds of thousands of years of human habitation. Burial mounds are another example of the built environment. (Downside: looting is a serious, devastating issue in part because the sites are so visible once you do know the signs or historical record. There is evidence to show that looting in Iraq was directed around sites from eras that would produce salable small finds, like clay tablets or precious small objects.)

Also if you are trying to build a subway line virtually anywhere in a European city it's a good bet you're putting it smack-dab in the middle of some amazing and crucial key sites! Rome is getting a new subway line completed in, I would guess, 2089. Many sites really are only uncovered during field surveys, where you walk along to collect and note surface finds, or when new buildings or roads are being built. Heathrow's latest expansion produced some really interesting early buildings, which would never have been excavated or known for a long time if the airport weren't on top of them...or, you know, someone digging on their land uncovers marble sherds or pottery. Serendipity. This is an issue even in American cities like New York and Philadelphia, both of which have had excavations in central areas in recent years. The trouble is more managing the sites you do know about and salvaging what you can, most of the time. Many sites get photographed, lightly explored (if that!) and sealed up for lack of funding. Many more, especially those visible mainly through postholes or lithic spreads are probably destroyed without anyone knowing, since the signs of a settlement can be very difficult to read. And some people just destroy them anyway because archaeology can be expensive and time-consuming.
posted by jetlagaddict at 8:19 PM on August 8, 2012 [5 favorites]

Your Inner Fish talks about how the paleontologists involved decided where to dig (three areas with rocks of a particular age that had been under shallow seas, two of which had been dug pretty thoroughly with highways an something else.)

In Illinois, as in many U.S. states (and many other parts of the world), building highways or other infrastructure requires an archaeological survey first. Here's some surprise "cultural deposits" found in 2011 during highway building.

If you find a surprise skeleton during construction or renovation of a building, say, you have to contact the state and their archaeology service comes in. (There's a woman who works for the state whose title is "Human Skeletal Remains." This makes me question ALL OF MY LIFE CHOICES.)

There are also a lot of amateur rockhounds, fossil hunters, and artifact hunters (arrowheads, around here) who learn a lot about local archaeology/paleontology/geology, and know enough to know when they've found something unusual. I have a friend who goes out every weekend to hunt along streambeds, both active ones and ones long dried up.
posted by Eyebrows McGee at 8:23 PM on August 8, 2012 [3 favorites]

The main way this happens is what is called (in the US, at least) CRM: Cultural Resource Management.

Let's say you're Walmart, and you've just found a brilliant site you'd like to build on in Collinsville, Illinois.

Well, Collinsville is close to a lot of Native American sites from the Late Woodland period of Mississippian culture settlement. So if Walmart wants to build there, due to the UNESCO heritage status of nearby archaeological sites, and the likelihood that more could be discovered in the area, it's likely that they will first have to allow archaeologists to come in and survey the area to determine that it's not of any significance.

If the archaeological survey finds evidence that this might be a good site for a dig, Walmart will (most likely) have to find a new site or suspend construction until all the various cultural resources have been gleaned.

My understanding is that big cities with long historical records -- and possibly UNESCO sites and the like -- have people on staff with archaeology backgrounds who deal with this sort of thing. In New York there's a strong intersection between archaeologists, historians, and city planners, for example. In Montreal, there's a museum dedicated to this sort of thing, which I highly recommend.

It also happens that there's no previous evidence that this might be an archaeological site, and you start digging the foundation for that Walmart, and then you happen upon artifacts or some other evidence of archaeological interest. In which case, the right thing to do is to hold back, call in the local university, etc.

However, obviously there are cases where this isn't respected. This actually happened in my town, where surveying for a new library revealed a slave burial ground. It being the south, white people were all, "heh, who cares, libaray, yay!" It took a lot of political action on the part of the black community to force the city to move the library.

I was an anthropology major, and a lot of my friends did archaeology. Surveying was a very popular summer job. Also, what others have said: human origins are paleoarchaeology. Paleontologists deal with non-human pre-historic species, though I suppose their methods are the same in terms of surveying and such. They probably have a harder task ahead of them, since there's a strong chance that somewhere in the historical record there is evidence of previous human habitation, whereas there's very little record of "hey, we found a lot of dinosaur bones here", further back than the 19th century.
posted by Sara C. at 8:26 PM on August 8, 2012 [4 favorites]

"and then you happen upon artifacts or some other evidence of archaeological interest. In which case, the right thing to do is to hold back, call in the local university, etc. "

It's not just the right thing to do, it might be a felony if you screw it up twice! There's even a bounty for people who report you for not reporting your find!
posted by Eyebrows McGee at 8:34 PM on August 8, 2012 [4 favorites]

There is actually quite an element of randomly hitting paydirt. As much as thoery can tell us, there is a lot that is still just supposition.
posted by DoubleLune at 8:41 PM on August 8, 2012

Here is a story about how satellite imagery is being used to find some sites. It's something I recall having read about elsewhere: little lumps and bumps in the earth's surface contour often yield sites worth digging in.

I think "sleuthing" is how you find the skulls you're after, and satellite imagery is one way of doing that.
posted by jet_silver at 9:08 PM on August 8, 2012

I don't think you should ever underestimate the power of local people randomly calling up a university extension office, radio station, or other minor authority to say "dude, check out what I found." In less-developed parts of the world, you're more likely to just flat-out get sold stuff in a market (and feel really frustrated trying to figure out where exactly the stuff came from,) but in the US and Western Europe, it's more generally fame/credit seekers that seem to inadvertently find the largest hoard of Anglo-Saxon treasure or a random buried mammoth.
posted by SMPA at 9:30 PM on August 8, 2012 [3 favorites]

I once participated in an archaeological summer program in a college in Pennsylvania, and we kept digging huge, neat, square holes into the dirt at bends of the Susquehanna river that we subsequently re-filled with sieved dirt. This was what we were taught: look at waterways, look at especially sheltered spots, dig.
[We found a bullet, and ancient can and one shard of pottery, in five weeks time. Scanning the fields at home in Bremen for stone-age arrowheads can be more effective, in fact.]
posted by Namlit at 11:53 PM on August 8, 2012

Wikipedia article on the use of remote sensing in archaeology.
posted by A Thousand Baited Hooks at 3:56 AM on August 9, 2012

First, I'd like to correct this misconception:
folks involved in this dig are anthropologists -- involved in the study of the origins of human life, including pre-Homo Sapiens human ancestors -- not archaeologists --
Archeology is a subfield of anthropology. If you are an archeologist, you are an anthropologist. Not all anthropologists are archeologists when I tell people that I studied archeology the response is, "NO SHIT! LIKE INDIANA JONES" and I'm like, "dude, stop yelling. Also, no." If you are digging for/examining the remains of species that are not part of human evolution, you are a paleontologist.

Ok. I feel better now. While it's true that a lot of archeology is in the same areas known to include "productive sites," choosing a site, well, that has a lot to do with luck, I've been told that much of deciding where to dig comes from having been on a lot of digs. You get a "feeling" about the landscape. Or, you just get lucky and see something that looks bony sticking up out of the sand or a rock. Or a kid picks up a rock and brings it to you because she thinks it's cool. The ability to recognize that it's important is...important. Then you have to get the kid to take you back to exactly where the rock came from. Because a few meters could mean the difference between hitting the center of a trash heap and...not.
posted by bilabial at 4:51 AM on August 9, 2012 [4 favorites]

Keep in mind that not all archaeological digs are at ancient sites for which no documentary records exist. Lots of archaeology is done at 18th, 19th, and even 20th century sites for which there are contemporary photographs, drawings, plot plans etc. indicating precisely where buildings and other points of interest were located.
posted by beagle at 6:36 AM on August 9, 2012

I'm formerly a paleoanthropologist/paleoarchaeologist, with excavation and survey experience in France and Egypt.

Our French sites were in the 40-60 kya range, and they were all re-excavations of sites known for most of the 20th Century and previously partially excavated. Methodology changed tremendously since the '50s, so current work with modern methods served to both collect new data and contextualize the old data, allowing new (better) conclusions to be drawn about the sites. The sites were in the Dordogne, just miles from Le Moustier, Cro-Magnon, etc., where you can't throw a rock without realizing it's a stone tool and finding a site.

The Egyptian work was site survey in the high desert. We knew from previous work—one of the really early 20th Century marauding Egyptologists—that there are lots and lots of stone tools, from probably ~100-120 kya (dating is tough for desert surface finds where all layers are compressed to a single surface), just strewn about the landscape; the point of the survey was to find concentrations of the tools, designate them at sites, and sample all across the landscape. We hiked a lot.

The tying theme here is: dig where you know there's something. And that's done a lot. A villager finds something interesting, takes it to the local historian, they call the University, a team is put together, and there you go. Satellite and aerial survey get you so far, but they're far more useful for sites with architectural features rather than old bones.

For really old, relatively small stuff like hominin skeletons, local finds help, but geology is also really useful. First, we know that most or all pre-1 mya stuff is in Africa. Then it's just a case of using geology along with satellite maps to find out where geological layers of appropriate consistency and age are close to the surface. That's why you see so many finds coming out of East Africa, especially the Rift Valley and Afar Triangle, Turkana, Ethiopia etc., and also north-central Africa like Chad, Libya, etc. There are layers at the surface of the 2-8 million-year-old range, which aren't completely solidified. I remember an amusing story one of my directors told from a survey in Ethiopia; essentially, they were walking along and saw some bones sticking out of a subsiding hillside. That's how the sausage is made, folks.

Archeology is a subfield of anthropology. If you are an archeologist, you are an anthropologist. Not all anthropologists are archeologists

Actually, some anthropologists are archaeologists and some archaeologists are anthropologists, but there are archaeologists who aren't anthropologists too, principally those who work on the classical world or Egypt. This whole structure is uniquely American; in England and continental Europe, archaeologists are wholly distinct from anthropologists, in all cases of which I'm aware. In America, there were preexisting departments focusing on the great ancient civilizations: the Greeks, Romans, Egyptians, and maybe some other places. When anthropology emerged in the early 20th Century, it was an all-encompassing study of humans and culture, part of which is material culture. Thus anthropology filled the gaps in archaeology, studying Native Americans, prehistory, Africa, and so on, and leaving the preexisting departments as they were.

So while most American archaeologists nowawdays are anthropologists, many are not. Boston University is notable in that it has a department of archaeology separate from anthropology, but you can study classical archaeology at many, many universities and not get an anthropological education. At the University of Pennsylvania, there are archaeologists studying prehistory, Native America, the Near East, India, and 20th Century America, all in the anthropology department, but there are also archaeologists in the East Asian Languages & Cultures, Near Eastern Languages & Cultures, Art & Archaeology of Mediterranean World, and Geology departments. Those differences greatly inform how archaeologists form their research questions and attempt to answer those questions too, which is an interesting rabbit hole to go down but that I won't follow here.

Generally, the people who are studying human origins are based in anthropology programs and are trained in anthropology, and thus are paleoanthropologists. Archaeology requires material culture, so paleoarchaeologists are more or less limited to after the start of the stone age when the first artifacts appear in the archaeological record. Lots of ancient hominin remains predate stone tools, but there will usually be bio and archaeo folks together on the projects. Paleontologists study old bones, but non-human, and will call in a paleoanthropologist, someone like Tim White, when hominin fossils are found.
posted by The Michael The at 7:04 AM on August 9, 2012 [9 favorites]

I spent four years working as an archaeologist in the U.S. southeast, starting as a technician and roving shovelbum out of college and working my way up to running the analysis/curation lab for a CRM company. I think you got some good answers when it comes to fossil hominid skulls, but for more recent ones I thought I would type this up.

Like Sara C. said, a lot of the archaeology being done in the U.S. today comes from the cultural resource management industry, and is being driven by regulations under the National Historic Preservation Act.

A lot of the work I did centered around surveying land that was being developed by federal and state/local governments (to build roads, buildings, or other construction), to ensure that there were no significant cultural resources being negatively impacted in the process. That includes buildings of historical significance, as well as any archaeological sites in the vicinity - both the ones already recorded and any new ones found during the survey.

Called a "Phase I," such a survey basically consists of digging sample test pits in a 30-meter grid over the area in question, digging a round hole down to sterile subsoil and sifting the dirt to look for any signs of a productive site on that location. I did a lot of road-widening surveys, for example, basically walking along a dusty road and digging holes every 30 meters. While you would sometimes find evidence of human habitation (generally in the form of pottery or stone flakes), the majority of such surveys don't find substantial enough sites that it requires additional mitigation beyond writing a report on the findings and recording any new sites with the Office of the State Archaeologist/State Historic Preservation Office.

In a few cases, the survey will reveal a significant site, whereupon you move into what's called a "Phase II" or testing phase. This entails more of what most people think of as a "dig," and includes things like digging larger, square test pits, perhaps excavating some features or other significant indicators on the site. This type of excavation will reveal numerous artifacts and require a more substantial analysis and report. The artifacts will also have to be prepared for long-term storage and submission to a curation facility.

Should the Phase II excavations reveal a site that has significant cultural resource value, you can go one of two directions. One is to leave the remainder of the site intact, and move the intended construction elsewhere in order to preserve the site for the future. The second is to do a "Phase III" or Data Recovery excavation, which is the substantial and extensive type of excavation where the site is dug up and recorded, destroying the site itself but preserving the data and artifacts. During the four years that I worked as an archaeologist, I worked on hundreds of projects but only participated in three or four Data Recovery type excavations. While this is what most people think of when they think of a "dig," a LOT of other work that goes into recording our cultural history are not part of such projects.

Going back to the skull question specifically, there are any number of additional sensitivities and regulations that deal with human remains in the U.S. Should you come upon any human remains in the course of survey/testing/data recovery, that requires calling in specialists. I never had to deal with that type of thing, thank goodness - it's something that we always hoped wouldn't happen. The only human remains I ever really had to deal with came from a project cleaning out a local government's abandoned archaeology lab, and even then we had to have special procedures in place to deal with the human remains scattered among the thousands and thousands of boxes...

As a side note, it was always useful to meet some of the locals in our project areas, as often they would have information about locations where we should be focusing our efforts. However, there were also times when the local population were not kind. I was working on a substantial project in the downtown area of a major city, where we had stripped the site down to the subsoil and were in the process of digging out several features chock-full of colonial/historical artifacts. The security company that we had hired to guard the location at night apparently decided that they didn't really need to guard a bunch of dirt piles. This allowed some local bottle-hunters to sneak in, whereupon they dug up the majority of the uncovered features and tossed everything they didn't want into random piles. It was devastating, not just to the project but for the local history that just went up into dust so that they could sell bottles for a few dollars each... [Don't buy artifacts!!]
posted by gemmy at 8:40 AM on August 9, 2012 [6 favorites]

Another way to get some information about the subsurface before digging is using geophysics. I only know of a couple of cases where geophysics has been used looking directly for paleontological artifacts, it is pretty routine for archeology as you can map some of the properties of the earth without destroying it.
posted by JayNolan at 10:11 AM on August 9, 2012

some crazy meat eating mammals that were in Africa before carnivores

Uh, not to derail, but can you elaborate on that part? Wouldn't meat-eating mammals also be carnivores? Or, I guess, what separates them from the current carnivores we know about. And what type of animals were they exactly. Like, from dinosaur eras or even previous to that? Thanks.
posted by allkindsoftime at 1:57 AM on August 10, 2012

Carnivore as we colloquially use it means meat eater, but it also refers to the taxonomic order Carnivora, which includes everything from seals to bears to raccoons. They're distinguishable by some skull characteristics, but they all have a "carnassial pair" of their first lower molar and last upper premolar that acts like a really sharp blade for slicing through meat effectively like a pair of scissors. It's really easy to see on dogs, and you can also see it on cats if you have a tolerant cat.

The taxonomic order Carnivora originated in North America and spread across Europe and Asia pretty early on, but didn't make it onto Africa until the African continent crashed into Eurasia around 24-22 million years ago, and then members of that order spread down the continent. Prior to their arrival, there were meat eaters on Africa, but they were from a different order, the Creodonts. Creodonts are crazy for a lot of reasons, but one distinguishing feature is that their carnassial pair is a different pair of upper and lower teeth, which made them a lot less ecologically flexible than carnivores. Creodonts were outcompeted by carnivores, and they went extinct about 8 million years ago, but they were a really amazing group of mammals.
posted by ChuraChura at 5:28 AM on August 10, 2012 [4 favorites]

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