Rock Talk By Larry Larason
Just another disaster
The fate of the Clovis People and the Megafauna
We all love a good tale of catastrophe. We get our adrenaline flowing by reading the stories of the plagues Moses called down on Egypt, floods, volcanic eruptions, earthquakes, and the asteroid strike that killed the dinosaurs. Disaster flicks draw audiences. I remember one called Krakatoa, East of Java. Released in 1969, even the title was a disaster, as the studio realized when someone finally looked at a map and discovered that Krakatoa is west of Java. Another perennial favorite is the 1919 molasses flood in Boston. That may sound humorous, but 21 people were killed and 150 injured when a tank holding 14,000 tons of sticky goo collapsed and inundated the streets of a downtown neighborhood.
Well, now we have a new disaster tale to get our attention. You may have seen the newspaper articles in May of 2007 announcing that a team of 25 scientists believed a comet had struck the Earth 12,900 years ago, which led to the demise of the Pleistocene megafauna and the Clovis Culture. Like most news articles about science the information was skimpy. I'd like to enlarge on that a little.
Who were the Clovis People? We shouldn't judge the beliefs and actions of people in the past by modern standards and knowledge. However, it does seem rather incredible that at the beginning of the twentieth century the scientific establishment thought that Native Americans, despite their diversity of languages and cultures, had been on this continent for no more than a few thousand years. Then in 1926-27 the Folsom Culture was identified. Their distinctive spear points – finely crafted bifacials with fluting on both sides -- were found embedded with the bones of an extinct species of bison near Folsom, NM. The bison was about ten percent larger than the modern ones and was known to have lived in North America at about the end of the Ice Age. Radiocarbon dating techniques were not invented until after WWII, so the dates for Folsom were vague. Then in 1929 another, older, culture was found beneath a Folsom site near Clovis, NM. At about the same time another site near Dent, CO yielded similar large bifacial points with fluting at the bases. Unlike the Folsom points, Clovis spear points were found with mammoth bones. These animals were definitely known to have gone extinct at the end of the Ice Age.
So it was clear that humans had occupied the Americas during the Pleistocene [Ice Age]. Clovis people were soon considered to be the "first Americans", who had come charging over the Bering Land Bridge about 12,000 year ago and spread across the landscape in record time to populate the New World. A lot of thought and effort went into shoring up this scenario. Archaeologists believed that the style of flint knapping used by Clovis hunters must have come from Siberia and scoured that area for similar technology. But no fluted points have ever been found in Eurasia.
We don't know much about the Clovis People. They were nomadic hunter-gatherers. No Clovis burials have ever been identified. The only technology we find is their flint tools. They probably made shelters of animal skins, but no artifacts made of bone, wood, or skins have survived. Clovis was originally considered a Southwestern culture, but it turns out there are more Clovis sites in the Southeast than the Southwest. Although concentrated in the US, fluted points are found as far south as Chile. The current theory is that they lived for only about 200 years and disappeared at the same time as the Pleistocene megafauna. The Folsom Culture seems to be a direct descendant of Clovis, although more geographically restricted to the Southwest.
Some archaeologists blamed the Clovis hunters for the disappearance of the North American megafauna: several elephant-like animals such as mammoths, as well as giant armadillos and ground sloths. Supposedly the hunters were so successful that they killed off their prey. Similar extinctions occurred after humans arrived in Australia about 50,000 years ago, and there is little argument that the Maori killed off several species of large, flightless birds after colonizing New Zealand. Critics of the "overkill hypothesis" look to Africa, where human hunters have coexisted with large herds of animals for longer than any other place on Earth. To paraphrase one skeptical archaeologist: each generation of Clovis hunters probably killed one mammoth then bragged about it around their campfires for the rest of their lives. Now, the comet scenario, if it is accepted by science, lets Clovis off the hook.
Comets are dirty snowballs. That is, they consist of ice, rocks, and miscellaneous chemicals. They are loosely consolidated and easily broken up by passes through the gravity fields of planets. For example, in July 1994 comet Shoemaker-Levy, broken into more than 20 pieces during an earlier pass by Jupiter, crashed into that planet's atmosphere in a series of dramatic impacts.
The comet scenario proposes that a comet struck Earth 10,900 years ago, broke up as it came in, and hit several places in fiery collisions that started wildfires across most of North America. The evidence for this is found in a thin, black layer of sediment, which includes glassy spherules and carbon nodules formed from molten material after the explosions. The carbon holds nano-scale diamonds that formed under extreme pressure. The black layer also contains soot from the fires and is found in places as widely separated as the Great Lakes Region and Arizona. Some has been found in Europe, as well. This black mat directly overlies several Clovis archaeological sites, and no Clovis sites are found above it, they say.
Where's the crater? Well, the comet apparently broke up into many pieces. There are about a million variably sized, elongated "hollows" along the eastern seaboard from New Jersey down to Florida known generally as "the Carolina Bays". They might be impact features. Some of the glassy spherules have been found in these. By their shape they seem to point toward the Great Lakes Region. So the researchers believe that the main body of the comet must have struck in Canada, perhaps near Hudson Bay. Since that part of the world was still covered by a thick sheet of ice, the crater would have been ice-rimmed and have melted soon afterward.
The scientists believe that the comet's debris and smoke from fires caused a cold period known as the Younger Dryas [YD]. This is a peculiar name for a time period. The name is based on a wild flower that flourished in Europe during periods when conditions were tundra-like. The flower's pollen has been found abundantly in sediments deposited during such times, hence the name. [And, yes, there was an "Older Dryas", about 1000 years before the younger one.] The YD began about 12,900 years before the present and lasted for 700-1000 years. The YD is the best known example of rapid climate change. Prior to the YD the continental glaciers were melting and forests were advancing northward. Then, in no more than a decade, the climate became colder and glaciers began growing once more, forests froze and shrubby tundra replaced them. Winds carried a lot of dust; this implies a drying climate –bad news for survivors of the impact event. In the American Southeast, human population may have dropped by about seventy percent following the comet's impact.
Few archaeologists still believe that Clovis was the first American culture. Given more evidence to bolster the comet scenario Clovis will have to be seen as "home-grown" by other peoples who were already here. The topic of the peopling of the Americas is still highly speculative and controversial. But stay tuned in. New ideas and evidence are being presented nearly every week, including the belief that the first arrivals came to the Americas as much as 20,000 years ago.
As I wrote this there was news of more than 500 dead in Peru following an earthquake. Rescue efforts to reach six miners in a cave-in were suspended due to the deaths of 3 would-be rescuers. Divers are still searching for bodies after the collapse of a bridge in Minneapolis. As the human population grows, so does the potential for large scale disasters. Will Durant wrote, "Civilization exists by geological consent, subject to change without notice." Make that "Life exists…," and add cosmology as a consenting agency.