Mysterious Fairy Circles Not Caused by Termites
Millions of barren patches can be found in the grasslands of southern Africa, at the transition to the Namib Desert. This image was taken in the Marienfluss Valley, close to one of the study areas where scientists analyzed aerial photos of fairy circles.
Oct. 12, 2012
-- It might look like just an ordinary picture of Stonehenge, but this is how the creators of the prehistoric monument wanted the site to be viewed, according to research using the latest 3D laser scanning technology. The groundbreaking analysis determined that the prehistoric monument was built to show off the solstices. In this view Stonehenge would look best when approaching from the Avenue, its ancient processional way to the north east.
Commissioned by the English Heritage, the laser-scan survey revealed in unprecedented detail the efforts made by prehistoric people at Stonehenge. "The result of the project were beyond all expectations. The investigation identified traces of stone working on virtually every stone," Marcus Abbott, head of geomatics and visualization at ArcHeritage, Hugo Anderson-Whymark, an Oxford-based expert on ancient worked stone, and colleagues wrote in the English Heritage report.
The laser-equipped researchers investigated the entire site. The laser scanner collected data with a resolution of 1 mm across the entire stone circle, and of just 0.5 mm for four stone surfaces of special interest. More than 700 surface features came to light.
NEWS: Stonehenge Twin Found Near Ancient Monument
The laser highlighted prehistoric carvings from 4,500 years ago as well as damage made by modern visitors. Along with modern graffiti, this image shows scores of little axe heads and a possible dagger added when the slabs were already 1,000 years old.
NEWS: Stonehenge Reveals New Clues of Ancient Worship
Overall, the laser scanning revealed 71 new Bronze Age axe heads, which bring the number of this type of carvings known at Stonehenge to 115.
NEWS: Stonehenge Built as Symbol of Unity
But the most interesting findings came from analysis of the stone surfaces. The study showed that the techniques and amounts of labor used varied from stone to stone. According to the researchers, these variations provide almost definitive proof that it was the intent of Stonehenge's builders to align the monument with the two solstices along a north-east/south-west axis. Indeed, the extremely straight and neat outline of the Great Trilithon, compared with all the other trilithons, shows that Stonehenge creators made deliberate efforts to shape it more carefully due to its special position on the solstice axis, just as they did for other stones that flank this axis.
The laser scanning showed that sides of the stones that flanked the solstice axis were most carefully worked to form very straight and narrow rectangular slots. To make them glisten in the sunlight, some stones had their crusts removed. These stones include two of the north-east facing sarsens in the outer circle, the Great Trilithon in the inner sarsen horseshoe, and an isolated upright stone in the south-west segment of the outer circle. By contrast, the stones in the south-western segment of the circle did not have their crusts removed.
The specially smoothed slabs created a dazzling light effect when the sun rays hit the stones. They would glisten in the dawn light on the longest day of the year and at sunset on the shortest This drawing shows Stonehenge in about 2300 B.C., after the construction of the sarsen outer circle and trilithons. Note the solstice axis.
PHOTOS: New Wonders of the Natural World
"Fairy circles" that form in the arid grasslands of Namibia have baffled scientists for decades. In the latest attempt to explain the cause of these mysterious circular patches, a group of researchers turned to aerial images.
"The occurrence of such patterning in nature is rather unusual," study researcher Stephan Getzin, of the Helmholtz Centre for Environmental Research (UFZ) in Leipzig, Germany, said in a statement. "There must be particularly strong regulating forces at work." (Image Gallery: Amazing 'Fairy Circles' of the Namib Desert)
Fairy circles are barren patches, typically surrounded by a ring of thriving vegetation. They can grow to be 65 feet (20 meters) in diameter and can linger for as long as 75 years.
For the past several years, scientists have offered up a variety of hypotheses for why these rings form in the arid grasslands transitioning into the Namib Desert. Their explanations have ranged from grass-killing seeps of hydrocarbons to carnivorous ants to termite feeding patterns.
One biologist recently conducted a census of organisms at fairy circles. His results, detailed in the journal Science last year, revealed a species of sand termite, Psammotermes allocerus, lived at the majority of patches. He concluded that the insects seemed to be feeding on the grass roots, creating the characteristic rings.
Getzin and his colleagues, however, say termites are typically distributed in irregular clusters in the wild; they argue that the insects couldn't create patterns as consistent as the ones they observed in their aerial photos.
"There is, up to now, not one single piece of evidence demonstrating that social insects are capable of creating homogenously distributed structures on such a large scale," Getzin said in a statement.
Getzin and colleagues think the most convincing explanation for fairy rings is that the grass grows in self-regulating patterns to deal with competition for water.
The researchers compared the situation to growth trends in forests. In a young forest, plants tend to grow at a relatively close range to one another. But over the years, vegetation thins in a self-regulating process so that mature trees have enough space and resources, the researchers said. Resource competition may similarly drive a self-organized formation of fairy circles.
The findings were detailed in the journal Ecography.
More from LiveScience:
In Photos: Mystical Fairy Circles Grace African Desert
Photos: Pufferfish Make Seafloor Circles to Mate
Photos: The World's Weirdest Geological Formations