Throughout the Eastern United States, particularly in southerly states that include North and South Carolina, there are a number of unique, elliptical features of unexplained origin. Known as the “Carolina Bays,” theories of their origin favors ancient, naturally occurring lake formations, although some have proposed that the features could be the remnants of ejecta from an ancient comet strike.
While the Carolina Bays remain a popular (and controversial) item of geological discussion, elsewhere in the world there are similar enigmatic elliptical features that have garnered attention over the years.
One particularly curious series of long grooves that score the landscape of the Argentine pampas near Rio Cuarto have long suggested evidence of an ancient multiple-impact site. The location was first observed by an Argentinian Air Force pilot, Captain Ruben Lianza, who wrote a summary of his observations for an astronomy publication, providing photographs he obtained from air. The images he provided showed teardrop-shaped features on the landscape which were similar in appearance to low-angle impact features previously observed on the planets Mars and Venus, and even on the Moon. They had not, however, been observed anywhere on Earth to-date.
Lianza went on to co-author an article with P.H. Schultz which appeared in Nature two years after his initial observation, where the authors described the discovery as follows:
"During routine flights two years ago ..., one of us (R.E.L.) noticed an anomalous alignment of oblong rimmed depressions (4 km x 1 km) on the otherwise featureless farmland of the Pampas of Argentina. We argue here, from sample analysis and by analogy with laboratory experiments, that these structures resulted from low angle impact and ricochet of a chondritic body originally 150-300 m in diameter.”
A total of ten features were noted across a distance of 50 kilometers. Analysis of geological samples from around the gouges produced evidence of meteoritic fragments and vitrified glass (i.e. stone or sand melted due to intense heat, which is often associated with meteorite impact sites). This led Schultz and Lianza to conclude that there was ample evidence that the sites were produced by an impact; it was also determined that the locations were just a few thousand years old, and likely occurred “well within the time of human habitation.”
As it turns out, the newly discovered impact regions had long been known to geologists in the region, although they had never been examined prior to the work conducted by Lianza and Schultz. Following the publication of their Nature article, American geologists also traveled to the site to provide further study and analysis.
The appearance of the impressions led to their being given rather unique names; one of the areas, measuring an impressive 2000 feet in length and 600 feet wide, was called “Drop.” A pair of nearby depressions were dubbed the “Eastern” and “Western Twin.” Yet another, which was comparable in size to the “Twins,” was named the “Northern Basin.”
Fundamental to the theory of an extraterrestrial impact site, each of the depressions shared a similar alignment with an orientation toward the northeast, which the researchers believed could support the idea of a low-angle impact.
However, some ballistics experts have challenged the impact theory over time, since the low entry angle proposed by Lianza and other proponents of an impact theory is an uncommon occurrence. In addition to this, key elliptical features of known impact features of this kind also produce a “butterfly wing” pattern of ejecta, which remains absent from the anomalous Argentinian features. To account for the depth of the Río Cuarto features as craters, an impact with a resulting blast 30 times greater than the 1908 Tunguska event would be required, which must have produced more visible ejecta.
While ideas vary about the age of the features, it is interesting to note that the depressions have been suggested to have originated around the beginning of the Holocene; this could possibly have coincided with the Younger Dryas, a period of abrupt cold reversal that occurred approximately 12,900 years ago as Earth was emerging from the last ice age. However, estimates as to the age of the Río Cuarto craters places them anywhere between 10,000 years and as much as 100,000 years old.
Further comparing the features to their cousins, the Carolina Bays, is the fact that satellite data indicates there are as many as 400 similar elliptical features in the same region. One theory proposed for the frequency and appearance of these elliptical features throughout the region is natural dune formations produced by wind over time, which could account for their shared angular orientation (a similar mechanism has been proposed in relation to the Carolina Bays, as outlined in a paper by Geoarchaeologist Christopher Moore and a number of colleagues, titled “The Quaternary evolution of Herndon Bay, a Carolina Bay on the Coastal Plain of North Carolina (USA): implications for paleoclimate and oriented lake genesis.”
Based upon physical and numerical modeling, proponents Río Cuarto event suggest that the object struck at an angle of no more than 15 degrees from the horizontal, with the impact itself having 10 times more explosive energy than the Barringer Crater event and 30 times more than the Tunguska event. Although the age of the depressions has not yet been determined precisely, it is believed by some researchers[who?] they are about 10,000 years old, placing them at the start of the Holocene, though the EID gives a broader age of less than 100,000 years old.
Unique features such as these remain fascinating, whatever their ultimate cause, and provide compelling clues about the ancient world which, with any luck, will one day be well understood and easily recognized. Until that time, our many questions about the ancient world will rely on further studies of such features, which may ultimately help us unravel several key remaining questions about the ancient world, and abrupt changes that were occurring in the paleoclimate of the ancient Americas.