Geoarchaeology: The Past Comes to Light
Geotimes Staff

Perhaps the only way to fully understand early humans is to understand their ancient environments. That simple concept underlies the field of geoarchaeology — the application of the earth sciences to archaeological studies. The following geoarchaeology vignettes show that geological stories are inseparable from the human ones: Sea level can rise causing populations to migrate. A volcano can erupt and wipe out a civilization. Climate can alter the soil and shift the course of a culture. As the natural world changes, so too does society. Together, geologists and archaeologists can unravel our past and better plan for and understand our future.

Searching Dirt
Aegean Volcanic Dating Dilemma
Digging Below Manhattan
Black Sea Floods
Satellites Reconstruct Ancient Egypt
Iceman's Origins


For 25 years, geologist Rolfe Mandel has been studying early Americans. He wants to know when they first arrived on the continent, where they came from and where they went once they populated the landscape. But in searching for clues from ancient people, Mandel decided on a route different from most archaeologists. They go out looking for artifacts; he goes out looking for soils.

Excavations in 2003 at the Claussen site along Mill Creek in northeast Kansas revealed at least three archeaological horizons. Rolfe Mandel, shown below inspecting mussel shells in an ancient campsite buried 30 feet deep, now awaits radiocarbon dates for the lower two horizons. Images courtesy of John Charlton, Kansas Geological Survey.

Mandel diligently treks from creekbed to creekbed, searching the banks for layers of soils that might be more than 9,000 years old, in hopes of finding evidence of early Americans. He believes that Paleo-Indians spent most of their time in stream valleys and near shallow depressions known as playas. As focal points for water, animal and plant resources, the playas and streams were attractive to people living in the High Plains. Because buried soils are viewable in river cutbanks, Mandel says, the banks are like windows to ancient landscapes.

Ancient Americans are among the most elusive groups for archaeologists to study because they were largely nomadic, following migrating herds of bison. They left little behind in the way of belongings or settlements, Mandel says. So archaeologists look for subtle clues of habitation, including flint spear points, knife blades, charcoal remains of campfires and bone fragments from the game that provided sustenance for the Paleo-Indians.

Until recently, most anthropologists believed that the peopling of North America began about 11,500 years ago with the crossing of the Beringia land bridge and then slow migration across the continent. However, archaeologists have now found sites dating human activity to at least that age in the North American Southwest and Southeast, which leads some researchers to believe that people arrived well before then (see stories in this issue).

Mandel and colleagues at the University of Kansas department of anthropology and the Kansas Geological Survey believe they will find evidence of inhabitants from more than 11,500 years ago across the Great Plains. Art Bettis, a geologist at the University of Iowa who also studies the peopling of the Great Plains, says it is "very likely" that geoarchaeologists will find these older sites.

Mandel, Bettis says, has developed the first comprehensive description of the Quaternary landscape history of Kansas, which will help in the search for buried archaeological sites. Indeed, Mandel's work is one of the most detailed regional histories of Holocene environments in the world, echoes Lee Allison, head of the Kansas Geological Survey. Having a good idea of what the ancient landscape looked like, especially the temporal and spatial patterns of soil deposits, allows Mandel to then target these geological oases for potential archaeological evidence. "It is geologic exploration applied to an entirely new field," Allison says. Thus far, searching the soils has led Mandel and colleagues to uncover several Paleo-Indian sites in Kansas that are at least 9,000 years old.

"Each site fills in a slightly different piece of the puzzle," Mandel says. At the Kanorado site in northwestern Kansas, for example, researchers uncovered well-preserved mammoth and camel bones at the base of a river cutbank — thought to be more than 11,000 years old. And at the Winger site in southwestern Kansas, researchers saw a massive bison bone-bed about 9 feet below the surface along a stream that is cutting into a playa. Researchers have dated the bones to about 9,000 years ago, and Mandel says there may be additional, older layers below.

One spot to watch, Bettis says, is the Claussen site in northeastern Kansas, which Mandel first discovered in 1999 but only recently began fully exploring. Walking along a creekbed, 30 feet below the present-day land surface, Mandel saw telltale signs of former stable landscapes — dark soil layers that indicate buried topsoils. In the dark layers, he noted small flakes of flint, cracked and blackened rocks from ancient fires, mussel shells and animal bone fragments. At the very least, Mandel says, "someone had eaten dinner here thousands of years ago." Even more exciting, he says, was that he could see at least three distinct layers of human activity, with the upper layer dated to nearly 9,000 years ago.

In the summer of 2003, Mandel and a team of archaeologists returned to the site, armed with a $1 million endowment from retired geologist Joe Cramer (who has spent more than a few years in search of ancient Americans himself) to search for further evidence of human activity. They collected charcoal samples from each distinct layer and sent them to a lab for radiocarbon dating. Now, Mandel awaits word on the dating. In the meantime, he's going back out to the streambeds, looking for archaeological evidence in the soils.

"Mandel's research into the early Americans promises to increase immensely our understanding about the peopling of the Plains," Bettis says. Mandel has changed the field of archaeology, he says, and it will be exciting to see what comes next.

Megan Sever

"The Ice-Free Corridor Revisited," Lionel E. Jackson Jr. and Michael C. Wilson, Geotimes, February 2004
"Quest for the Lost Land," Renée Hetherington et al., Geotimes, February 2004

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Aegean Volcanic Dating Dilemma

After a volcanic eruption, widespread ash plumes can smother the region and leave behind valuable marker horizons in the archaeological record. By assigning absolute dates to these horizons, geologists are working with archaeologists to better understand the history of the ancient civilizations that flourished nearby. At Thera, an eastern Mediterranean island also known as Santorini, geologists are looking to the ash to reconstruct what happened there thousands of years ago.

Floyd McCoy samples a small remnant of a massively thick deposit left behind by the Late Bronze Age eruption of Thera in the eastern Mediterranean. In the background stands the huge caldera excavated by that eruption and now filled by the sea. Photo courtesy of Floyd McCoy.

Thera erupted more than 3,500 years ago, causing pyroclastic flows, earthquakes, tsunamis and extensive tephra plumes that scattered pumice and ash as far away as the Black Sea and the Nile Delta. In 1939, Greek archaeologist Spyridon Marinatos hypothesized that the Late Bronze Age eruption had led to the demise of the artistically and technologically advanced Minoan civilization, which had thrived for more than 1,500 years on the Aegean island of Crete, just 70 kilometers south of Thera; the civilization began to decline in 1450 BC. This idea quickly gained widespread acceptance and was later popularized as proof of the historical accuracy of the myth of Atlantis. However, a discrepancy between archaeological and geological findings has led to a 20-year-long debate about the exact date of the eruption and therefore, its role, if any, in the collapse of the Minoan civilization.

Traditional archaeological techniques of dating — such as synchronization with Egyptian civilizations through the discovery of Minoan pottery at sites in the Nile Valley or of Egyptian artifacts on Crete — have put the eruption date around 1550 B.C. or later. And some radiocarbon dates from the town of Akrotiri, a Theran city buried under meters of ash, place it closer to 1500 B.C.

Other geological dating techniques have suggested a much earlier date for the eruption. Acid snow and volcanic glass found in Greenland ice cores place the date of the eruption around 1645 B.C. Also, thicker than normal tree rings found in ancient trees in Anatolia show that a cool wet year, possibly caused by a massive volcanic eruption, occurred around the same time. Additional evidence for climate change at this time comes from Ireland, California and China.

"It's really geophysicists against archaeologists," says Floyd McCoy, a volcanologist at the University of Hawaii who has been studying Thera for more than 20 years. "But it's not a hostile thing. It's a wonderful kind of conversation going on as we try to figure this out."

McCoy recently discovered 2-meterthick ash deposits in new roadcuts on the island of Anaphi, 12 kilometers east of Santorini, and ash in seafloor cores close to the Peloponnese peninsula. Both findings indicate a much wider ash distribution.

"This eruption was almost 10 times bigger than we thought," McCoy says. "It had been about a 6. This puts it at 7.0" on the Volcanic Explosivity Index, which ranges from 0 to 8. It would thus have had a more damaging and lasting effect on the region's agriculture, trade, infrastructure and fleets, he says, which could have eventually contributed to the Minoan collapse. "It's my opinion that this eruption changed the whole course of Western civilization," McCoy says.

Jeremy Rutter, a specialist in Bronze Age archaeology of the Aegean at Dartmouth College, agrees with the earlier date for the eruption, but he says that even if the eruption were more explosive, the time span between the eruption and the collapse of Minoan palatial civilization is still too long for it to be a factor. "There's no way you're going to make something that happened in either 1640 B.C. or 1550 B.C. responsible for something that happened quite suddenly in 1450 B.C.," he says.

The true importance of the eruption date, Rutter says, is its potential for use in correlating developments within various Bronze Age civilizations across the eastern Mediterranean. "This is a problem that has been haunting this small corner of scholarship for some time now," he says. "We're interested in determining whether certain things happened first in Egypt or first in the Aegean. And continuing disagreement over the absolute date of the Theran eruption really is getting in the way of making progress on this."

Rutter said he expects the conflict will be resolved in the next 10 to 15 years, with the discovery of Theran ash in a welldated archaeological site in the Near East or by advances in dendrochronology. Or it could be solved geologically, McCoy says. He is currently trying to apply new techniques for dating the eruption itself.

Sara Pratt
Geotimes contributing writer

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Digging Below Manhattan

Buried under the cement and concrete of the Manhattan skyline lie layers of glacial deposits, animal bones and modern human detritus, representing thousands of years of Holocene geology. The most urban setting in the world still provides opportunities for geoarchaeological research, and recent work on the soils and stratigraphy of the island sheds light on how to dig in New York.

A trench at a dig site on Worth St. in downtown Manhattan reveals soils and other geologic evidence for the ancient and more recent history of New York. Image courtesy of Geoarcheology Research Associates.

Joseph Schuldenrein and his team of geoarchaeologists have further elucidated Manhattan's geology, both prehistoric and historic. In the past few years, the researchers were called in to several construction projects where they had a rare opportunity to core and document profiles from freshly dug sites across lower Manhattan.

They had seen these neighborhoods before, when centuries-old African-American burial grounds were discovered during the construction of a tunnel almost two decades ago. Schuldenrein, an adjunct professor at New York University, established Geoarcheology Research Associates in 1989. Based in Riverdale, N.Y., the consulting geoarchaeologists determine whether construction projects will disturb historic sites and document the value of what might be found, necessary steps under the National Historic Preservation Act. The company works to fuse geology and archaeology, studying everything from early Native American landscapes in the Ohio River valley to early cultures in Pakistan, India, and Jordan.

During their most recent opportunities to see under the city, the researchers recorded some known stratigraphic history — from late Quaternary glacial moraine deposits and prograding deltas to the arrival of the Dutch and the beginning of anthropogenic landscape shifts. But they also found a soil horizon they could follow across the island.

"Nobody knew about this soil," Schuldenrein says. The stable landform serves as a baseline for future digging, allowing the team to reconstruct the island's past surface morphology. It also provides a date for stratigraphic reference from the layer's organic material, of about 2,000 years before present. Schuldenrein presented the new soil horizon and a complete history of the island at last year's annual Geological Society of America (GSA) meeting in Seattle, Wash.

Superimposing historic and current maps with well profiles, Schuldenrein's team has painted "a real picture" of what to expect when digging, Schuldenrein says. The least likely traces to be encountered are Native American, which Schuldenrein compares to "looking for a needle in a haystack — they didn't leave much behind." However, by reconstructing the postglacial landscape, he can point to the stream deposits that represent landscapes where people might have made camps or hunted in the region before the Dutch settlers came.

According to Dutch maps from the 1600s, a pond sat just north of the city's first commons, where City Hall sits today, Schuldenrein says. Native Americans probably stayed there, and the area held a local lime source from natural springs as well. Several hundred years later, early American tanners used both the pond and the lime.

"As the tanning industry got bigger and bigger, the pond became a huge cesspool," Schuldenrein says, creating a health epidemic (and a typhus reservoir). In 1815, the city mandated its closure, filling it without leaving a trace. But Schuldenrein traced the origins of the fill to an early artist's rendition of a nearby hill that was once popular for sledding in the city. "The only thing this can be is a glacial kame," or ridge deposited by a glacial stream, says Schuldenrein, who has found oral accounts from 1850 describing the recreation area. "In 1815, that's what they used to fill it — they just leveled the landscape."

The new New Yorkers flattened glacial features and extended Manhattan to its current configuration, changing the terminal moraine in order to create a huge commercial center. Geoarcheology Research Associates has produced a 15,000-year chronology and a map of lower Manhattan, noting the potential Dutch, English and American archaeological sites and places where, hypothetically, Native Americans could have settled.

Schuldenrein "mentally stripped away the construction and got to the landscape as it was when people first settled there … defining some of the glacial features underneath the city that influenced the settlement of the earliest European historic populations," says David Cremeens, a soil scientist with GAI Consultants, in Monroeville, Penn., and the chair of the archaeological geology division of GSA.

Construction of the modern city disturbed previous deposits in some places and preserved them under cement in others, also making the evidence hard to access, Cremeens says. Schuldenrein's work could uncover social structures or other elements buried underneath the modern city. It "has the potential of turning up something brand new," he says, "or at least adding to what we know."

Naomi Lubick

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Born in Odessa, Ukraine, Valentina Yanko-Hombach has always wanted to understand the ancient history of the great basin that borders her homeland. The Black Sea, which stands as an important trading and commercial center for the surrounding countries, holds clues deep in its sediments about the people who once lived along its shores.

This SeaWiFS satellite pass over Turkey in August 2000 highlights the Black Sea (top) and the nearby Mediterranean Sea. A body of evidence is now emerging from Eastern European scientists about the flooding history of the Black Sea, challenging a mainstream hypothesis of a large, catastrophic flood linked to the biblical story of Noah’s flood. Provided by ORBIMAGE and the SeaWiFS Project, NASA/Goddard Space Flight Center.

For the past 30 years, the geologist and micropaleontologist has been working to reconstruct the region's sea level, drawing on research from other former-Soviet and Eastern Bloc scientists. Language and political barriers have largely prevented these scientists' data from entering the mainstream global scientific debate.

A prevailing Western idea about a past ancient flood in the region, first presented in 1997 by Walter Pitman and Bill Ryan both of Columbia University, suggests that salty Mediterranean water abruptly flooded the freshwater Black Sea about 7,200 years ago; the researchers link the event to the biblical story of Noah's flood. But Yanko-Hombach is weaving together a different story for the basin — not one of a single sharp cataclysmic inundation but instead of natural cyclicity. The ups and downs of the sea could have mirrored the changes in culture for a variety of societies.

She and colleagues have studied thousands of kilometers of high-resolution seismic profiles and thousands of sediment cores during large-scale geological surveys of the Black Sea shelf. Yanko-Hombach's own work hones in on foraminifera — shells of bottom-dwelling microorganisms that reflect past water chemistry. She can match specific species, for example, to the salinity signatures from various bodies of water; some love saltwater, others abhor salt.

Yanko-Hombach's analyses suggest that the region has experienced many floods of various magnitudes over the past 800,000 years. She has found a first wave of recolonization by Mediterranean immigrants among foraminifera species in Black Sea sediments as early as 9,500 years before present. Strontium isotope ratios in mollusk shells, however, as measured by Candace Major and Steve Goldstein in Ryan's research group, are now revealing the sudden switching on of a strong marine signal at 8,400 years before present. Thus, Yanko-Hombach's data suggest an earlier and less dramatic sea-level change. The evidence shows, Yanko-Hombach says, that "Noah's flood legend has nothing to do with the Black Sea."

Ryan and Pitman's hypothesis was based on incomplete data, she says. The Black Sea has many areas of regional washout, where sediments of certain ages are absent and can give the impression of a flood event. Eastern scientists, however, have long been sampling areas closer to the seashore.

Jim Teller of the University of Manitoba says that where researchers sample can result in significantly different conclusions about changes the fossils underwent. "Researchers get a limited number of dates, and there's a lot of difference in the extrapolation process over intervals without dates," he says.

But Ryan speculates that the discrepancy with the Russian and Ukrainian measurements may lie in the dating method itself. The ages Yanko-Hombach uses are primarily derived from methods of carbon-14 dating. This technique required large samples, he says, which may have introduced mixed organic materials and skewed the results to older apparent ages.

"Her timing of the saltwater intrusion is more than a thousand years before any similar salinity signal in cores calibrated with the new accelerator mass spectrometer instruments," Ryan says. "So it is difficult for me to see how so many salt-tolerant species of clear Mediterranean genesis could colonize the Black Sea 9,500 years ago and yet not show up in the strontium isotopic signal."

Yanko-Hombach's data are "both wonderful and problematic," Ryan says, pointing out that her "marvelously detailed record of the foraminifera species abundances" still indicates the occurrence of an abrupt change in fauna in some cores, just like what he sees in the bottom-dwelling mollusks. "A flood from the Mediterranean could produce this change, but the real issue is whether a flood is the required causative event or if something of less magnitude and more gradual could produce the changes we both observe," he says.

Currently, Yanko-Hombach and Ryan are working together to apply modern dating methods to single specimens in an old Ukrainian core sample. Ryan says that his research has involved frequent correspondence with Eastern scientists. Yanko-Hombach's work, he says, is a valuable service to the community in creating new opportunities for collaborative study.

"I am trying to bring together people to develop scientific dialogue," Yanko-Hombach says. She has already presented her research widely, including at a NATO workshop last October in Bucharest, Romania, and the Geological Society of America (GSA) meeting last November in Seattle, where she co-chaired a session about the Black Sea.

To further break down barriers of the past, she has proposed a 4.5 million Euro proposal to the European Union that involves archaeologists, anthropologists and geologists from 11 countries, including Germany, Switzerland, France, Italy and those bordering the Black Sea basin (excluding Georgia). The project would continue her quest to link climate to changes in coastal migration and culture in the region.

In the meantime, archaeologists continue their own quest to link their findings to flood events. Archaeological evidence from a site called Kamennaya Balka in Rostov, Russia, for example, supports a large flooding event 16,000 and 14,000 years before present, Yanko-Hombach says. She and Andrey Tchepalyga of the Institute of Geography in Moscow say that melting glaciers and thawing permafrost caused the Caspian Sea to increase its surface level by about 80 meters, swelling to half again its present size, and to spill multiple times into the Black Sea during the 2,000-year period.

Nataly Leonova at Moscow State University suggests that such flooding may have been responsible for local changes in culture about 16,000 years ago. Before that time, Leonova says that archaeological artifacts in and around the Crimea indicate a clear relationship to Caucasus cultures. And then that connection suddenly stopped: The area was perhaps covered by water, cutting off communication.

All the floods likely caused some change in culture, Yanko-Hombach says. Flooding can happen in many places in the world as a result of climate change, and thousands of years ago, "local people would have considered this as 'Noah's flood,'" she says.

"These were magical kinds of things, so anything truly larger compared to your experiences and what your ancestors had told you about would be worth writing down," says Teller, who also co-chaired the GSA session. He has published work in 2000 suggesting that Noah's flood occurred in the Persian Gulf, where archaeologists found the Epic of Gilgamesh — clay tablets that include a story of a great flood.

Still, Teller says that linking any flood event to Noah's flood is nearly impossible at this time "unless something is discovered that nails down the whole concept of Noah's flood — which is just a few verses in the Bible."

Lisa M. Pinsker

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Satellites Reconstruct Ancient Egypt

Sarah Parcak of Cambridge University in England used this Landsat image of the eastern Egyptian delta to locate 44 new archaeological sites in Egypt. Darker spots on the image reveal archaeological sites and modern cities from the surrounding landscape due to their higher moisture content.

Parcak is taking this satellite imagery and verifying it with archaeological data and cores from the delta in order to differentiate present-day cities from the ancient sites, and to reconstruct settlements from Egypt's Old Kingdom — best known for the Great Pyramids. This is the first time this methodology has been used to locate archaeological sites.

Presenting at the American Geophysical Union meeting last December, Parcak says she particularly wants to see how an extreme and sustained period of drought and cooling 4,200 years before present affected the delta landscape and the people of the Old Kingdom. Archaeologists have found many sites tied to the Old Kingdom from before the abrupt climate change, but very few after. Thus Parcak's research could open up the field for further research on climate change-civilization interaction.

Megan Sever

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A long the Italian-Austrian border in 1991, two German hikers made a startling discovery: a 5,200-year-old mummy preserved in an alpine glacier. Later named the Iceman, this Neolithic man has led to a plethora of research and debate over the past 13 years, speculating about his lifestyle, habitat and cause of death.

The Iceman, however, left clues about his life and habitat in the chemical composition of his remains. Through food and drink, the isotopic signatures from local rocks, soils and water transfer to the biological minerals deposited in the human body. Tooth enamel preserves childhood activity, and bones reveal the last 10 to 20 years before death. By comparing the Iceman's isotopic signatures to those in the surrounding environment, geoscientists now say that they have nailed down his likely birthplace and lifelong travel patterns.

The Iceman, also known as Ötzi (he was found in the Ötzal Alps), probably lived his entire life — 46 years — within a 37-mile range south of the glacier in which he was found, says Wolfgang Müller, a geologist at the Australian National University. His birthplace was likely within a few valleys to the southeast of where he was found — present-day northernmost Italy. He migrated during his later adult life and seemed to spend much of his adult life a bit farther west, Müller and colleagues suggest in an article in the Oct. 31 Science.

While Ötzi may have migrated seasonally, the evidence that he spent his entire life in one small region demonstrates that central Europe's Alpine valleys were permanently inhabited during the terminal Neolithic, Müller and colleagues write.

"Knowing the Iceman's home territory will help in reconstructing the cultural landscape in which the Iceman lived," says Thomas Loy, an archaeologist at the University of Queensland in Australia, who has been using DNA analysis to understand the Iceman's death (most recently speculated to have been caused by a violent battle). Until Müller's analysis, Loy says, the Iceman was a singularity; he was an isolated Copper Age person with no corresponding identifiable culture.

The researchers compared isotopic composition in Ötzi's teeth and bones with soils throughout the region. Within his habitat, at least four different types of rock are distinguishable by strontium and lead isotopes: limestone, rhyolite, basalt and a group of mixed phyllites and gneisses. Also in his teeth and bones, the geochemists noted distinct levels of certain oxygen isotopes that they could then compare to known oxygen isotopes in the area, thus constraining Ötzi to the specific watersheds in which he lived at varying stages of his life.

Although much of Müller and colleagues' findings correspond to previous research in the region, some papers have suggested that Iceman spent a good deal of time farther north than Müller's team suggests. But, Müller says, all the isotopic evidence they found points to the south. In addition, the isotopic evidence corresponds to the botanical and archaeological evidence.

In the new study, the scientists use a "combination of several techniques pooled together to maximize information, and also new methods never utilized in such circumstances," Müller says. One such method involves examining argon isotopes in tiny mica flakes found in the Iceman's intestines, which constrains his last meal to a region that holds the same mica. Loy says using combined isotopic evidence to constrain habitat and travel ranges is "a very powerful method," and will be a very useful tool to investigate prehistoric people and societies.

Megan Sever

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