Google Earth has revealed an archaeological mystery from on high. Satellite images show the existence of ancient stone structures built thousands of years ago in what is now an inhospitable part of Saudi Arabia, reports LiveScience. Archaeologists led by David Kennedy of the University of Western Australia call them "gates" because they resemble field gates from above. In a paper in the November issue of Arabian Archaeology and Epigraphy, Kennedy writes of about 400 such structures built somewhere between 2,000 and 9,000 years ago. They are generally in what are now volcanic lava fields, though it's possible the land wasn't quite so unfit for humans when the structures went up. The big question is why.
"I don't know what they are," Kennedy tells the New York Times. "They don’t look like structures where people lived, and they don’t look like animal traps," he says, adding that they're probably too low for the latter. Most of the "gates" are about 700 feet long, though one extends for 1,700 feet, per news.com.au. Johnson has previously discovered similar structures in neighboring Jordan via airplane trips, though he thinks those (which resemble kites) were likely animal traps and probably came along after the "gates." One researcher not involved with the study calls it intriguing, but says he wishes Kennedy would have offered a theory, if only to discourage speculation about extraterrestrial origins associated with other such finds. (Read about another Google Earth-related discovery.)