Tiny diamonds invisible to human eyes but confirmed by a powerful microscope at the University of Oregon are shining new light on the idea proposed in 2007 that a cosmic event — an exploding comet above North America — sparked catastrophic climate change 12,800 years ago.
In a paper appearing online ahead of print in the Journal of Geology, scientists from 21 universities in six countries report the definitive presence of nanodiamonds at some 32 sites in 11 countries on three continents in layers of darkened soil at the Earth's Younger Dryas boundary.
The boundary layer is widespread, the researchers found. The miniscule diamonds, which often form during large impact events, are abundant along with cosmic impact spherules, high-temperature melt-glass, fullerenes, grape-like clusters of soot, charcoal, carbon spherules, glasslike carbon, heium-3, iridium, osmium, platinum, nickel and cobalt.
The combination of components is similar to that found in soils connected with the 1908 in-air explosion of a comet over Siberia and those found in the Cretaceous-Tertiary Boundary (KTB) layer that formed 65 million years ago when a comet or asteroid struck off Mexico and wiped out dinosaurs worldwide.
In the Oct. 9, 2007, issue of Proceedings of the National Academy of Sciences, a 26-member team from 16 institutions proposed that a cosmic impact event set off a 1,300-year-long cold spell known as the Younger Dryas. Prehistoric Clovis culture was fragmented, and widespread extinctions occurred across North America. Former UO researcher Douglas Kennett, a co-author of the new paper and now at Pennsylvania State University, was a member of the original study.
In that paper and in a series of subsequent studies, reports of nanodiamond-rich soils were documented at numerous sites. However, numerous critics refuted the findings, holding to a long-running theory that over-hunting sparked the extinctions and that the suspected nanodiamonds had been formed by wildfires, volcanism or occasional meteoritic debris, rather than a cosmic event.
The glassy and metallic materials in the YDB layers would have formed at temperatures in excess of 2,200 degrees Celsius and could not have resulted from the alternative scenarios, said co-author James Kennett, professor emeritus at the University of California, Santa Barbara, in a news release. He also was on the team that originally proposed a comet-based event.
In the new paper, researchers slightly revised the date of the theorized cosmic event and cited six examples of independent research that have found consistent peaks in the creation of the nanodiamonds that match their hypothesis.
"The evidence presented in this paper rejects the alternate hypotheses and settles the debate about the existence of the nanodiamonds," said the paper's corresponding author Allen West of GeoScience Consulting of Dewey, Arizona. "We provide the first comprehensive review of the state of the debate and about YDB nanodiamonds deposited across three continents."
West worked in close consultation with researchers at the various labs that conducted the independent testing, including with co-author Joshua J. Razink, operator and instrument manager since 2011 of the UO's state-of-the-art high-resolution transmission electron microscope (HR-TEM) in the Center for Advanced Materials Characterization in Oregon (CAMCOR).
Razink was provided with samples previously cited in many of the earlier studies, as well as untested soil samples delivered from multiple new sites. The samples were placed onto grids and analyzed thoroughly, he said.
"These diamonds are incredibly small, on the order of a few nanometers and are invisible to the human eye and even to an optical microscope," Razink said. "For reference, if you took a meter stick and cut it into one billion pieces, each of those pieces is one nanometer. The only way to really get definitive characterization that these are diamonds is to use tools like the transmission electron microscope. It helps us to rule out that the samples are not graphene or copper. Our findings say these samples are nanodiamonds."
In addition to the HR-TEM done at the UO, researchers also used standard TEM, electron energy loss spectroscopy (EELS), energy-dispersive X-ray spectroscopy (EDS), selected area diffraction (SAD), fast Fourier transform (FFT) algorithms, and energy-filtered transmission electron microscopy (EFTEM).
"The chemical processing methods described in the paper," Razink said, "lay out with great detail the methodology that one needs to go through in order to prepare their samples and identify these diamonds."
Another UO co-author on the new paper is Jon M. Erlandson, executive director of the Museum of Natural and Cultural History, who was a co-author on the paper that first proposed the cosmic event.