Many archeologists and other scientists have speculated that the abrupt disappearance of numerous animal species in North America about 12,900 years ago, matched with the demise of the Clovis Paleoindian culture at about the same time, can be attributed to massive ecological disruptions caused by a meteorite or comet impact. Until recently, however, evidence supporting the extraterrestrial impact hypothesis has been scanty and inconclusive. Now scientists believe they’ve found the smoking gun in Channel Islands National Park just off the coast of southern California.

Scientists have long been puzzled as to why the Clovis era ended so abruptly 12,900 years ago (+/- 100 years), and why so many animal extinctions occurred at about the same time. The disappearance of the Clovis people closely paralleled the disappearance of 19 bird genera and nearly three dozen mammal species, including megafauna like horses, camels, giant short-faced bears, and the pygmy mammoths of the Channel Islands. Whatever caused this was something more like an event than a process or trend, and it was something that doesn’t happen very often.

The search for an answer narrowed a few years ago when scientists constructed a strong argument for an extraterrestrial impact. The hypothesis seemed plausible enough. If global ecological disruption and the demise of the dinosaurs could be attributed to a colossal asteroid impact about 65 million years ago, why couldn’t continental-scale ecological disruption, the disappearance of numerous megafaunal species, and the demise of the Clovis culture be attributed to a less gargantuan cosmic impact that occurred much more recently?

What was missing was the empirical evidence. You don’t have good science without good proof.

Once scientists were pointed in the right direction and began carefully searching for evidence of an extraterrestrial impact, it didn’t take long to find it. That’s because they knew what to look for and had a pretty good idea where to look for it.

When a good-sized meteorite or comet strikes the earth, an immense amount of kinetic energy is immediately converted to heat and work. One result is extremely hot forest fires, the dispersed organic remains of which end up as a surface layer of soot, ashes, charcoal, carbon spherons, and other fire-signature debris that is subsequently buried by sediments and preserved (as rock, if old enough) for scientists to dig up much later on. If a soot-rich layer of a particular age is distributed on a continental or vast regional scale, it’s prima facie evidence of a rare mega-event.

Among the other things that an extraterrestrial collision yields is the enormous heat and pressure needed to convert graphite (present in meteorites) into diamonds. The diamonds produced in this way are microscopic in size and very distinctive in shape. Properly termed “shock-synthesized hexagonal nanodiamonds,” they go by the mineral name lonsdaleite. An important thing to know about lonsdaleite is that the only place we’ve ever found the naturally-occurring variety is in association with impact craters.

If scientists were to dig into the earth and find a layered deposit rich in soot, lonsdaleite, and perhaps other nano-sized diamond polymorphs (n-diamonds and cubics), they would know that they have uncovered very convincing evidence of a cosmic impact. If they were to find it at the Younger Dryas Boundary (YDB), which is material laid down 12,900 years ago (+/- 100 years), they would have, from the perspective of the Clovis-era extraterrestrial impact hypothesis, the “smoking gun” that they’ve been looking for.

That said, you can imagine the excitement of the researchers (a 17-member team led by University of Oregon archaeologist Douglas Kennett) who recently found such a deposit at the Younger Dryas Boundary while digging about 13 feet down in Arlington Canyon on Santa Rosa Island in Channel Islands National Park.

It wasn’t a random find. Since the Clovis-era megafauna extinction included the Channel Islands pygmy mammoth (Mammuthus exilis) of the Northern Channel Islands, the scientists had deduced that this would be good place to look for evidence of a Clovis-era extraterrestrial impact.

Scientists have found charred debris at the YDB in some 50 other Clovis-era sites around North America, and some sites have yielded small amounts of nanodiamonds as well. Scientists will need to find additional corroborating evidence before the Clovis-era cosmic impact idea can be comfortably moved from the hypothesis category (speculative) to the viable theory category (tested and proved). Meanwhile, you have to admit that the evidence gathered so far is mighty compelling.

Just where the Clovis–era impact may have occurred remains open to speculation, as is the matter of whether it was a surface strike, an airburst, a swarm of airbursts, or some combination. Noting the absence of a crater of the right size and age, some scientists speculate that an extraterrestrial object, possibly a comet, exploded above or within the Laurentide Ice Sheet in the vicinity of the Great Lakes.

Postscript: Somebody has got the date wrong. The caption of the accompanying NPS photo stated that the pygmy mammoth skeleton excavated on Santa Rosa Island in 1994 was determined to be 12,240 years old. The problem is, 12,240 BP is something on the order of 600 to 700 years after the pygmy mammoths in the Northern Channel islands were purportedly wiped out by the Clovis-era impact. Some sources state that Channel Islands mammoths were still around as late as 10,300 years BP.