Apr 03 2009
Mammoths and Nanodiamonds
This is a story of the very big and the very small, but more importantly it is an interesting story of how scientists resolve different ideas with research and evidence. I have been following it for years and love to read about new updates.
The burning question is – what happened to the mammoths and other megafauna of North America about 13,000 years ago. Extinction itself is no big deal – most species that have ever lived are extinct, and all species go extinct eventually (at least so far). But this was somewhat of a mass extinction – a continent-wide extinction of large terrestrial mammals.
Theories as to the cause include overhunting by newly arrived human populations, climate change brought on by the transition from the recent glacial period to the current inter-glacial period, and (more recently) the impact of a large comet somewhere over Canada. It seems that overhunting likely was a factor, but not enough by itself to explain the loss of megafauna.
So at present the two main contenders are climate change vs impact. Recently the PBS program, NOVA, showed its new special on the conterversy before an audience of scientists. The program made the case for the impact theory, and revealed some new evidence. Scientists skeptical of the impact theory remain skeptical, however, indicating that this controversy is far from over.
Nanodiamonds
The new evidence revealed in the program is the discovery of nanodiamonds from a 12,900 year old layer of glacial ice in Greenland. Nanodiamonds are exactly what they sound like – nanometer sized diamonds. They are formed under high temperature and pressure, such as would be present in a meteor or comet impact. They have been found in meteorites. Supporters of the impact theory point to nanodiamonds as a major source of evidence. Researchers have found nanodiamonds from multiple North American sites all dating from12,900 years ago. This North America-wide sediment layer of nanodiamonds is the same kind of evidence as the world-wide layer of iridium 65.5 million years ago is evidence for an impact leading to the mass extinction that claimed the dinosaurs.
Critics, however, charge that the nanodiamonds are not definitively of impact origin (where as the iridium layer at the K-T boundry is clearly an extraterrestrial isotope). They argue that the nanodiamonds could have been produced by earth-bound processes and simply been deposited in those sediment layers where they are found. Or, nandiamonds raining down in micrometeorites could have simply collected in the layers detected. They may be concentrated in a layer because the retreat of the glaciers caused large lake formations, or some similar cause.
This is where the new Greenland evidence come into play. Researchers found nanodiamonds in a 12,900 year old layer of glacial ice. This would be expected from the impact hypothesis, but is difficult to explain with the sedimenting hypothesis. That is, in fact, exactly why they looked there.
Critics
But the other side is not ready to give up yet. Mineralogist Bevan French of the Smithsonian National Museum of Natural History in Washington, D.C. is quoted as saying: “I still don’t think nanodiamonds by themselves are a signature for extraterrestrial material.”
There are also other lines of evidence that appear to contradict the impact theory. This is often how good science works – using multiple independent lines of evidence to triangulate to the most likely answer. In this case Dr Sandy Harrison from the University of Bristol and colleagues looked at evidence for large forest fires in North America from 15,000-10,000 years ago. What they found was evidence for scattered fires, but no continent wide forest fire event 12,900 years ago, as would be predicted by the impact theory.
Many researchers blame the Younger Dryas for the mass extinctions. This was a 1,300 year period of cooling following the warming that occured at the end of the most recent glacial period. The exact cause is unknown, but one theory is that fresh water from glacial melting dumped into the North Atlantic and shut down the salt-driven oceanic currents. But regardless of the cause, this was a period of rapid climate change – perhaps too rapid for wildlife to respond, hence the extinctions.
The Future
What we have are apparently contradictory lines of evidence – nanodiamonds suggest an impact, while the absence of continent-wide forest fires argues against an impact. This controversy, however, will be resolved with evidence. There are specific questions that need to be answered – Can nanodiamonds be created on earth, or are their only origin meteorites and impacts? Will the nanodiamond layer evidence hold up under further investigation? Why isn’t there evidence for extensive forest fires at the same time?
Also, one bit of missing evidence is a large-enough impact crater in North America from 12,900 years ago. Impact theorists argue that a comet could have exploded above the ground (like with the Tunguska event of 1908), which is plausible – but this can also just be an excuse for the absence of evidence.
Researchers will continue to argue their respective cases, while they think about new predictions that flow from the various theories. They will then test those predictions, and over time one theory will slowly win out over the competitors.
Just like science is supposed to work.
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10 Responses to “Mammoths and Nanodiamonds”
Sure, the Tunguska object left no crater, but it was also small enough — probably less than 50 meters across — to disintegrate in the atmosphere. It destroyed an area of forest around 2,000 square kilometers, which would be devastating to a local human civilization, but which is nowhere near large enough to kill all the mammoths in North America. I suspect an object large enough to do that would have left a huge crater and other evidence of geological and biological devastation.
Did mammoths come from Siberia and travel over the connect to North America? Giant sloths travelled up from South America and became extinct 10,000 years ago. Same phenomenon? Climatic changes? Dwindling food resources?
“”"Why isn’t there evidence for extensive forest fires at the same time?”"”
Perhaps what I am going to say here is an utter stupidity, but I have to try anyway: cannot the absence of extensive forest fires be accounted for by the presence of the glaciers? If I am not mistaken, 12,000 years ago was roughly the end of the last Ice Age. If ice sheets had covered a significant part of the area of impact, the meteorite would have melted ice rather than lit fires.
But this just seems too obvious.
The whole mammoth story is really intriguing. I’ve been trying to nail down when the last known mammoths went extinct but seem to be finding contradictory information. One referenced article in Wikipedia states:
“A small population survived on St. Paul Island, Alaska, up until 3,750 BCE, and the small mammoths of Wrangel Island survived until 1,650 BCE.”
NOVA on the other hand reports that “radiocarbon dating of fossil remains show that the mammoths were on St. Paul 7,908 years ago.”
Anyone know exactly when the last mammoths disappeared?
The closer you are to something, the tougher it is to see it.
Did mammoths come from Siberia and travel over the connect to North America?
That’d be my guess. Mammoths lived all over the world at that time, so I have trouble thinking they were a homologue to all the other pachyderms in the world. Although I’m no expert
Extraterrestrial nanodiamonds don’t necessarily require a single large impact. If a comet broke up in space and hit the Earth with multiple impacts, the extraterrestrial material might not show up in a single layer. The impacts don’t need to be simultaneous to cause extinctions. Nanodiamonds might even survive better as dust that cools down, rather than gets consumed in a fireball. A break-up in a near-Earth solar orbit could generate a lot of dust, which would be acted upon by solar light pressure which would pretty rapidly move it from non-capture orbits to capture orbits.
Every time humans arrive in a new environment, most of the large land animals go extinct. This happened consistently throughout history. The arrival of humans in new areas is spread out over tens of thousands of years, but this rule holds without exception. It happened in Madagascar, Europe, Asia, the Americas, Australia, and various islands across the world most recently. None of these extinction events were worldwide, they always occurred right where humans had just shown up. I think the implications are clear, albeit unpleasant. I know correlation does not equal causation, but continent-wide extinction events are not common even over geological periods, not to mention the brief period of human existence.
Except for Africa where humans evolved along with the large land animals. The animals adapted to survive our presence. Jared Diamond mentions that in his book, “Guns, Germs, and Steel.”
TheBlackCat, Your thoughts come from Paul Martin 1967 whose overkill hypothesis was formulated from studying island peoples which was then extrapolated to continents. Donald Grayson, anthropologist, University of Washington has an important article on this topic in the current issue of Journal of PreWorld History.
“Overkill is bad science because it is immune to the empirical record.”
I would liken the lack of an impact crater to the lack of fossils to fill every conceivable gap — just because nobody’s found it does not mean it didn’t exist. Impact craters are notoriously difficult to find on Planet Earth, by virtue of our atmosphere, biosphere, and geologically active planet. They get eroded or buried. A handful are clearly visible from space, but most need radar studies to reveal crater rims, and the presence of shocked quartz and similar geologic evidence of a massive impact.
I’m not sure a continent-wide fire would be necessary to wipe out the mammoths, and not every impact would cause such a fire.
Another possibility not mentioned is volcanism. Volcanoes can cause tremendous ecological upheaval, although they do tend to leave a bit of a mark when they do so, like a layer of ash in the soil.