Long ago, in the rarefied dawn of prehistory, a paleo-Steve-Jobs noticed that when he broke a piece of obsidian, the edge of the fracture was very sharp and he could use it to whittle the end of a stick to dig grubs from the ground. This may have been the first crude obsidian tool and was later used to scrape flesh from the skin of an animal that had been killed by a predator. Over many generations, paleoindians learned to fashion extremely sophisticated tools by flaking the edges of obsidian until a suitable knife or spear point was formed.
The lustrous black of obsidian has reflected fire in the eyes of humans since very early in the evolution of our species. Current concensus suggests the first North Americans, or the Paleoindians, probably entered the Americas across the Bering land bridge sometime between 21,000 and 14,000 years ago at the height of the last glaciation. Evidence of a connection from the old world to the Americas is sketchy, though obsidian projectile points from sources on the Russian Kamchatka peninsula have been found in Alaska.
Regardless of the uncertainty of paleoamerican origins, they needed sources of obsidian with which to fashion tools and weapons. As the Yellowstone ice-cap melted and receeded 12,000 to 14,000 years ago, people started exploring the higher elevations. Most likely, an adventurous young paleoindian trekking the upper reaches of the Yellowstone river discovered the much sought after black glass. Indeed, he discovered one of the richest sources of obsidian in North America, at Obsidian Cliff on the Yellowstone plateau.
Remember Earth Science 101? You learned that igneous rocks begin their life in molten form. If they cool over a very long period of time, beneath the surface of the earth (intrusive rocks), minerals begin to crystallize. The atoms that comprise a mineral grow in regular, geometric patterns that are unique to the specific crystallography. If there is a gas or fluid pocket in the molten material, beautiful museum-quality crystals might grow. Usually, however, the slowly cooling rock forms an interlocking mass of uneven partially-formed crystals such as a granite. Granite is composed of intergrown crystals of quartz, feldspar, mica and other minerals. When you fracture granite, with a hammer or another rock, it will break unevenly. It would be useless in making a precise tool like a knife or spear tip.
But if the granitic molten rock makes its way to the surface and cools quickly (extrusive), the mineral crystals don’t have time to grow and, with just the right conditions, volcanic glass or obsidian will form. The water content of the lava also plays a role. Dry lava solidifies more rapidly than lava which has a high water content. Either way, we have a rock with no crystals. Such a substance, like glass, is called isotropic, which means that it has the same molecular structure in all directions. This quality allows obsidian to fracture in a very predictable, curved or conchoidal manner when it is impacted. Obsidian is often referred to as volcanic glass.
Very early in human existence, we discovered how to work the glass into useful tools and implements like scrappers, knives and spear points. Our modern term for this skill is flint knapping.
In this excerpt from the film People of the Hearth, flint knapper Dale Herbort demonstrates the highly-skilled techniques that paleoindians and historic tribes used to make knives, spear and arrow tips.
Today obsidian is used to make superior surgical scalpels used in delicate surgerys such as eye surgery and heart bypass operations, as well as plastic surgery. These tools are hand made by pressure flaking just as the paleoindians pressure-flaked their fine spear tips and cutting tools, and each scalpel is one of a kind. The edge is many times thinner and sharper than surgical steel and studies have shown that healing is quicker and scarring less with their use.
Obsidian sources exist across the earth predominantly along the ring of fire where the earth’s continental plates meet and volcanism occurs. Since the distant discovery of obsidian’s usefulness, it has been in great demand to make weapons, tools and exotic artistic or ceremonial objects. Often in ancient times, however, the sources were far from population centers. Trade networks were required to move obsidian from quarries to where it was needed.
Such networks existed in the Pacific islands, Eurasia and Central America, among others. Long overland journeys and dangerous ocean voyages were undertaken to acquire this essential resource of pre-Columbian people.
Unlike the ring of fire volcanos, the Yellowstone volcano is uniquely located in the interior of the north American continent formed from a hotspot in the mantle rather than plate boundary volcanism. Since no obsidian can be found east of the Mississippi, Yellowstone, became a major obsidian source to native cultures of eastern North America.
Obsidian Cliff is located eight miles north of Norris Hotsprings in Yellowstone. It was named by Philetus W. Norris, the second Superintendent of Yellowstone National Park in 1878 and he also referred to it as “The Glass Mountain.” The cliffs extend for almost 2.5 miles south of Obsidian Lake, making it one of the largest exposures of obsidian in the western states. Obsidian Cliff is the result of a volcanic eruption, approximately 180,000 years ago. This eruption occurred long after the catastrophic eruption and subsequent collapse of the Yellowstone Caldera, but it is the result of the same active mantle hotspot beneath Yellowstone.
Tools and weapons made from Yellowstone obsidian have been found as far away as Maine and Central America. We know this because obsidian has a distinctive chemical signature, which can be used to identify the origin of the mineral. Beautiful ceremonial knives and spear blades made of Yellowstone obsidian have been found in Hopewell Indian sites in Ohio. The Hopewell were a sedentary tribe who lived in dwellings made of posts, and wattle and daub walls with thatched roofs. They are considered one of the first agricultural groups in North America. The Hopewell culture indicates how extensive the trading networks were in prehistoric North America. They acquired copper from the upper Great Lakes, mica from the Carolinas, shells from the Gulf of Mexico, and obsidian from the Rocky Mountains including Obsidian Cliff in Yellowstone. In addition to ceremonial spear points and knives, some 660lbs of raw obsidian from Yellowstone was found cached at the Ohio Hopewell site. Since no Hopewell items have been found in and around Yellowstone, it is assumed that the material was transported to Ohio and worked there.
Age dating of tool manufacture can be estimated using a technique called obsidian hydration dating. Obsidian, when fractured, begins to absorb atmospheric water. This water accumulates at a known rate, as a hydration rim, which can be seen and measured. The date when water began to be absorbed can then be calculated using the size of the hydration rim. With these methods, archaeologists and anthropologists have worked together to unravel the travel, hunting, and trading habits of tribes that used the Obsidian Cliff quarries for over 10,000 years.
In addition, certain tribes used recognizable knapping patterns such as clovis or folsom. By dating the origin of the obsidian artifacts, a chronological framework can be assigned to the movement of various tribes. Together, they teach us about the migrations, trade networks, hunting patterns, and rituals of the earliest inhabitants of North America.
When I think of Yellowstone 12,000 years ago, I imagine a barren tundra with scrubby plant growth, bogs and glacial ponds. There are no trees yet and drainages are just beginning to reestablish their dendritic tendrils draining the 8000ft plateau. Perhaps a wolly mammoth trundles across the glacial moraines and bogs. And perhaps the young hunter was in pursuit of the mammoth when he stumbled upon the impressive exposed cliffs of black glass. Of course, there are no journals and it is pure supposition. Nevertheless, the discovery of Obsidian cliff is an exciting cinematic visual for the mind.
Daniel J. Smith is a geologist, filmmaker, writer and musician who has lived in Bozeman, Montana for the past 40 years. He completed his Masters Degree in 1990 at Montana State University, studying the Buck Mountain Fault in the Teton Range. His field work was conducted during the summer of 1988. As he climbed the ridges and Peaks of the Tetons that year he watched Yellowstone to the north, burn, in the worst fire season in recorded history. Smith has had many adventures in and around Yellowstone and writes about them in his YellowstoneGeo Blog.