This Month in Archeology

2009 Jan. 7
Are diamonds an archeologist's best friend?

You'd think an archeologist would remember excavating diamonds from an ancient site. I must admit that I don't recall ever having done so, but recent research suggests that I have. And not just a few either. At certain sites, it seems, I've excavated millions of them – I just didn't realize it at the time. Let me begin 13,000 years ago, with two big archeological questions that these diamonds may help to answer.

The earliest well-documented archeological culture in North America is termed Clovis, and we know that at least some of the time Clovis people hunted large animals like mammoths and mastodons. We also know that about 13,000 years ago (give or take a few hundred years), the Clovis way of life disappeared – the style of stone tools, and apparently the way people made their living, changed completely. So, Question #1: What happened to Clovis culture?

At about the same time, a large number of mammals went extinct. Many of these were Ice-Age "megafauna", including mammoths, mastodons, short-faced bears (similar to grizzly bears, but about twice as big), dire wolves (similar to grey wolves, but again much larger), and a whole menagerie of animals adapted to the cold and harsh environments of the time. Question #2 is easy to guess: What caused these extinctions?

Archeologists have come up with two primary hypotheses to account for these questions, each with its own strengths and weaknesses.

Hypothesis #1: Climate change. From chemical analysis of arctic ice cores we know that global temperatures were gradually warming at the end of the last Ice Age, beginning about 15,000 years ago. This warming came in fits and starts, with short-term cooling trends present too. Hypothesis #1 asserts that the megafauna couldn't adapt quickly enough to these changes, which caused their extinction, which in turn caused Clovis people to develop a different lifestyle.

Hypothesis #2: Overkill. Large animals today such as elephants have very long gestation periods (almost two years), so even small disruptions can cause entire populations to crash. The overkill hypothesis asserts that Clovis hunting caused a precipitous decline in one or more large animal, which caused serious ripples throughout the entire ecosystem (this is happening in Africa today as elephants are disappearing), which lead to the extinction of several species. No more megafauna, no more Clovis way of life.

Archeologists have debated these two hypotheses for years. Proponents of overkill point out that megafauna species survived climate change through nineteen or more major ice ages during the past two million years: why would this particular episode cause their demise? Proponents of climate change doubt whether enough large animals were actually killed to lead to extinction.

Much of the excitement of science is the interplay of competing ideas, and the search to explain the world in ways that make the most sense. In the last few years, a team of researchers from the University of Oregon and other institutions has come up with Hypothesis #3. By most accounts, it explains what happened 13,000 years ago in a way that makes more sense than 1 or 2.

The researchers looked very closely at sediments above, below, and within Clovis-era archeological sites. The 13,000-year-old sediments often have a dark, organic-rich layer resulting from charred trees and plants. Within this layer, but not above or below it, the sediments contain an unusual array of particles, including nanodiamonds: tiny diamonds, each just a few nanometers in size. And a nanometer, as I'm sure you can guess, is pretty small. One-billionth of a meter, to be precise. In this measure, the period at the end of this sentence is about 300,000 nanometers across. I hope this excuses me for not noticing any nanodiamonds when I excavated them.

Nanodiamonds are significant because they don't form under normal geologic conditions; they come from the impact of large space objects exploding at or above the earth's surface. Because of the exact makeup of the nanodiamonds and other elements found within the sediments, astronomers believe the 13,000-year-old layer is evidence for the impact of one or more large comets.

So, Hypothesis #3: One or more comets exploded over North America about 13,000 years ago, creating enough force and heat to account for the burned layer of trees and plants. The devastation to the ecosystem was enough to cause the extinction of numerous animal species (particularly the larger ones, which are generally more susceptible), and the technology and lifestyle of Clovis people, in turn, was adapted to the new environments.

Hypothesis #3 is supported by compelling evidence, and like all sound scientific ideas it opens up even more questions than it answers: Exactly how was the environment altered by the impact? Did Clovis people themselves adapt to the new conditions, or were they replaced by a different group of people? Were there other meteor impacts that influenced the environment and human societies?

Archeologists today have a great number of questions about the past – far more, in fact, than when we first began studying our ancestors more than a century ago. And this, too, is an exciting hallmark of sound scientific endeavors. Like the billions of nanodiamonds released by an ancient meteor, the closer we look the more we'll find. When we begin running out of questions, we'll know we've begun to run out of creativity. And because the questions are bigger than nanodiamonds, there would be no excuse for that.

Dr. Gregory Vogel is Director of Research at the Center for American Archeology in Kampsville, Illinois. He may be reached: (618) 653-4316, or gvogel@caa-archeology.org.