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A Science Detective Story

AN INTRIGUING DISCOVERY

Archaeologists Michael Kunz and Richard Reanier have discovered evidence that seems to challenge long-held theories regarding the migration of humans to North America. In 1978, Bureau of Land Management archaeologist Michael Kunz happened onto the remnants of a prehistoric hunting lookout in northern Alaska atop a mesa rising 60 meters above the tundra. He found the "Mesa site" during a routine archaeological survey before the area was to be opened for oil and gas exploration. After 14 years of excavation, sample collection, and analysis, Kunz announced his discovery in the spring of this year as one of the oldest well-documented archaeological sites in North America. His find raises intriguing new questions about the first Americans and poses challenges to accepted theories about their arrival in the New World.

America's earliest settlers did not leave many remains, unlike later cultures who lived in more permanent villages. The small population of early settlers moved often, harvesting wild plants and hunting animals. Erosion, burial, decay, and disturbance by subsequent populations make it difficult for archaeologists to find clues that would tell us more about these people. The Mesa discovery was no exception; stone lance points and hearths are the primary evidence from which to theorize.

Despite this meager evidence, Kunz and his colleague Richard Reanier have been able to reconstruct what probably happened at the Mesa site. They believe that prehistoric hunters maintained a lookout at the site during two intervals: the first, from 11,700 to 11,200 years ago; and the second, from 10,200 to 9,700 years ago. These hunters had migrated to this part of North America from Asia across a now submerged land bridge, probably in pursuit of game animals. From the top of the mesa, an unobstructed view of the valley below enabled them to scout out giant bison, mammoths, and other animals crossing the surrounding tundra. While on the mesa, they made and repaired the tools needed to fell the big game. Kunz and Reanier are still looking for clues to explain why the hunters eventually abandoned the mesa.

Projectile point found at the Alaskan Mesa SiteThe projectile point found at the Alaskan Mesa site (left) closely resembles the typically Paleoindian Clovis point (right). These similarities suggest that the Mesa site also represents a Paleoindian occupation.

Bureau of Land Management (left), John Dyck Collection, Peter A. Bostrom, Lithic Casting Lab (right)

Typical Paleoindian Clovis point

Until the Mesa discovery, many scientists believed that only one cultural group had arrived with the earliest migration from Asia to Alaska. As these people moved southward into North America, they lost their Siberian culture traits. Archaeologists refer to this changed group of people as the Paleoindians. The single migration theory seemed to explain why the tools of the known early inhabitants of Alaska were similar to those made by Siberian cultures of the same period but distinctly different from Paleoindian artifacts commonly found in the Lower 48 states. The early dates at the Mesa site seem to contradict this theory of a single migration of people whose tool kit changed as they moved southward.

Epoxy casts of a single stone artifact

Epoxy casts of a single stone artifact show the stages of lithic reduction, the process by which archaeologists replicate ancient stone artifacts.

Bruce Bradley, Crow Canyon Archaeological Center

The people of the Mesa site do not appear to be related culturally to Siberian cultures or to other known inhabitants of Alaska 11,000 years ago. Alaska's only other culture of this period, called the Nenana Complex, used different types of stone tools. Instead, the projectile points found at the Mesa site resemble Paleoindian weapons found in the Southwest and Plains regions of the United States dating back 10,000 - 12,000 years.

Kunz and Reanier believe that their find of a fully developed Paleoindian culture in Alaska suggests that the Paleoindians did not evolve from a single cultural group that came to America from Asia, but were, in fact, one of at least two or more distinctly different groups that came into the New World along this route and were living in Alaska at the end of the Ice Age.

One of many perplexing questions Kunz and Reanier are still attempting to answer is why evidence of Paleoindians exists in Alaska but not in Siberia. One theory proposes that the Paleoindian culture evolved and developed in the area that is now beneath the Bering Strait. Another theory suggests that evidence of the Paleoindian culture exists in Siberia but has not yet been discovered. Still another possibility is that the Paleoindian cultures developed in the New World and did not spread back to the Old.

The Clues
Over 85 percent of the tools recovered at the Mesa site are the stone points of spears or throwingstick darts or other tools associated with hunting activities. These and the remains of 11 hearths are the primary clues at the site. With so little evidence, Kunz and Reanier must examine every bit of it from every possible angle, creating a picture of life in this remote corner of the world detail by detail.

Most early cultures can be identified by the unique and uniform style of their projectile points. Thus, archaeologists began their investigation with the stone points. The physical form of the points caught Kunz's attention and led him to suspect that the Mesa site might represent a Paleoindian occupation.

Archaeologists first learned about the Paleoindians, known popularly as "big game hunters," in the 1920s, when they found spear points between the ribs of bison at sites near Folsom, New Mexico. In 1932, a similar spear point was found together with the bones of extinct animals near Clovis, New Mexico. The Clovis site dates back approximately 11,000 years.

There are obvious similarities between the Clovis points and the Mesa points (see photograph, above). Both have a lancelike shape, sharp points, sharp upper edges, overall symmetry, a slightly narrower base than midsection, a lentil - shaped cross section, and heavy edge grinding on the bases. One attribute that distinguishes the Clovis point from the Mesa point is the shallow lengthwise channel (fluting) on its face.

After consulting with experts in the field, Kunz and Reanier concluded that while the stone artifacts were not the product of any known Paleoindian culture, the style of the artifacts and the technology used to manufacture them were undoubtedly Paleoindian. They concluded that they had identified a previously unknown northern member of the Paleoindian tradition.

The Dating Game
To test their hypothesis, Kunz and Reanier decided to try to date the site to see if it could be placed within the Paleoindian period. While a variety of techniques can be used for dating prehistoric artifacts, each one works with only certain kinds of materials.

For example, the carbon 14 method applies only to organic materials. All living organisms absorb carbon 14. Once an organism dies, it loses carbon 14 at a fixed rate. By measuring the amount of carbon 14 remaining, scientists can determine the date an organism died. Artifacts such as charcoal, papyrus scrolls, linen cloth, bone tools, wooden bowls, and oyster shells can be dated using this method, but metal tools, stone statues, and ceramic vessels cannot.

Luckily, Kunz and his colleagues found 11 hearths with charcoal fragments at the Mesa site. Some of the stone tools found in the charcoal had distinctive fractures caused by the fire. This established the connection between the artifacts and the charcoal used to date them. It also assured archaeologists that they were dating charcoal from fire made by humans rather than a blaze created by natural events, such as lightning. The carbon 14 dates for the Mesa site reveal that it was used between 9,700 and 11,700 years ago. This period is roughly contemporaneous with other Paleoindian cultures, which were active between 8,000 and 11,200 years ago.

Archaeologists Richard Reanier, Sergei Slobodin, and Michael Kunz

Archaeologists Richard Reanier, Sergei Slobodin, and Michael Kunz discuss excavation strategies in Alaska. The 11,700 - year - old site is atop the mesa looming in the background.

Dan Gullickson, BLM

Most of the Mesa stone tools and flakes were made from chert, a stone found nearby in Iteriak Creek. Archaeologists also found several pieces of obsidian. After doing a geochemical analysis, Kunz was able to determine that the obsidian had come from a volcanic source more than 320 kilometers away. This evidence suggests that the Mesa people may have traded with other cultures or migrated over long distances in search of big game.

The obsidian also enabled scientists to confirm their earlier estimates of when the site was occupied. Prehistoric people frequently used obsidian (volcanic glass) to make tools. Because the surface of a piece of obsidian absorbs water from the surrounding environment, the freshly exposed surfaces of obsidian being fashioned into a tool will begin to absorb water and a hydration "rind" will develop. Scientists can examine a thin slice of an ancient obsidian tool beneath a microscope, measuring the width of this rind. If the rate of hydration is known, the age of the tool can be calculated from the width of the rind. The thickness of the rind on a flake of obsidian from the Mesa site indicated an age very similar to the carbon 14 dates from the charcoal.

Photo of the Mesa Site
The Alaskan mesa that gives the site its name.

BLM

What Kunz and Reanier found at the Mesa site, as well as what they did not find, led them to draw inferences about the people who lived there. Because only hunting implements and fragments left from making projectile points have been unearthed, Kunz and Reanier suspect that the site was a lookout rather than an encampment. No animal bones have turned up, nor have any other materials that would indicate how the people might have lived when they were not hunting. Of course, animal bones are subject to decay and probably would not survive for 12,000 years in the shallow arctic soils. In upcoming expeditions, Kunz and Reanier will search the surrounding terrain in the valley below for traces of the base camp these people may have occupied.

Also missing from the Mesa site were the distinctive hunting artifacts common to later groups whose relics were found in the valley below. This suggests that only the distinctive group they call the Mesa Culture made use of the spot.

The Mesa site find points up the dynamic nature of science—showing how current theories are constantly being challenged as scientists make new discoveries. Many scientists believe that humans came to the New World over 12,000 years ago. Scientists have reported signs of human occupation of a site in Pennsylvania some 19,000 years ago, in Chile 13,000 years ago, and in Brazil more than 30,000 years ago. These claims have not been generally accepted, however, because of concerns over aspects of the dating techniques.

As technology advances, perhaps new archaeological tools and techniques will enable scientists to bring more color and detail to the picture of prehistoric life at the Mesa site and across the continent.

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Last updated: 11-13-2009