An international scientific team has identified in Lake Cuitzeo, in central Mexico, unusual materials in the sediment that support the theory of a meteorite impact some 12,900 years ago, according to an article published in the Proceedings of the National Academy of Sciences.
The team, headed by Isabel Israde Alcantara, of Mexico's Universidad Michoacana, said in the article that the layer of black lake sediment is rich in carbon and contains nanodiamonds and micro-spherules dating from the beginning of the so-called Younger Dryas period, an abrupt and very short cold interval that started about 12,900 years ago.
This period was a brief phase lasting about 1,300 years when the climate cooled at the end of the Pleistocene period and the presence of these materials in a core sample 27 meters (88 feet) long "is interpreted as the result of an extraterrestrial impact."
Besides Israde, other members of the team include her faculty colleague Gabriela Dominguez Vazquez, as well as scientists from Taiwan's National University, the University of California, the University of Oregon and Harvard, and the Institute for Materials Science in Tsukuba, Japan.
Lake Cuitzeo covers 300 to 400 square kilometers (115 to 154 square miles) and is 27 meters deep, on average.
The scientists removed the core sample from beneath the lakebed with the aim of obtaining a record of the climate from the period before the interglacial period, the article explains.
"Our attention focused very quickly on an anomalous layer, about 10 centimeters (4 inches) thick and at a depth of 2.8 meters (9 feet) deep, which dates from some 12,900 years ago and coincides with several anomalous environmental and biotic changes, recognized independently in other ... regional lake samples," the article continues.
Taken together, these changes produced the most noteworthy layer of sediments at the end of the Quaternary Period.
The layer, the scientists explained, contains a diverse and abundant accumulation of materials linked to an impact, and in addition to the nanodiamonds and spherules of carbon there are also magnetic spherules.
The researchers, in their article, are pondering multiple hypotheses to explain their observations but have come to the conclusion that the presence of such materials "cannot be explained by any terrestrial mechanism."
They rule out a rain shower of cosmic particles; wildfires; volcanism; human-related activities; and even particle misidentification (like finding false positives for nanodiamonds), saying that a cosmic impact is the only viable hypothesis to account for the materials.
Essentially, the scenario painted by the scientists is this: About 13,000 years ago, a piece of a comet or asteroid hurtled into the atmosphere at a shallow angle, superheating the atmosphere around it as it plunged toward the surface. The air grew hot enough to ignite plant material and melt the rock below the object's flight path. Within a few microseconds, atmospheric oxygen was consumed and the freed carbon atoms condensed into nanodiamond crystals.
The shock wave from the meteorite blew these nanodiamonds and other carbon particles high into the atmosphere and spread them widely. Larger mammals in North America not killed by the blast starved, unable to forage on the scorched earth, and human populations there also dwindled. The shock to the atmosphere was enough to lower global temperatures for more than 1,000 years.
The research study bolsters the controversial argument that an asteroid impact might have chilled the planet during the Younger Dryas.
The theory of an extraterrestrial impact leading to global cooling 13,000 years ago was first posed in 2007 and holds that something hit the Earth and set a large swath of North America on fire. The theory was proposed after a study of ancient sediments at multiple sites, where geologists noticed a carbon-rich layer of sediment. Later, researchers led by University of Oregon archaeologist Douglas Kennett found high concentrations of nanodiamonds - which are associated with high-temperature collisions of material - in that sediment layer.
The theory drew a firestorm of criticism and the nanodiamond theory was largely discounted by 2011 after many groups of scientists could neither corroborate nor replicate the results. Now, however, the research team led by Israde has come up with results that appear to corroborate the 2007 hypothesis.