For forty years, astronomers have puzzled over the miles-high mounds rising from of the centers of Martian craters. Scientists have finally pieced together an origin story for the weird geologic pimples—and it reveals a critical moment in the Red Planet’s history.
Turgai, Kazakhstan might not look like much besides wide, sweeping plains. But over the past few years, archaeologists have revealed more than 200 massive earthworks, so large that you’d never notice them from the ground. As the New York Times reports today, no one knows their purpose–yet.
Silbury Hill is a huge artificial mound in southern England, about 130 feet high and covering five acres. Europe's largest artificial mound, it may have been built by the makers of Stonehenge...but they definitely weren't the last to use it.