Contrary to popular belief, crop circles are not just a modern-day phenomenon. On 22 August 1678, people saw strange circles in a
Hertfordshire oat field. A surviving
woodcut, called The Mowing Devil, makes clear what some people thought at the time: Human hands and feet were probably not responsible for the unusual appearance of the crop field.
In The Natural History of Staffordshire, Robert Plot (the first person to discover and record a dinosaur fossil)
wrote (in 1686) that crop circles (which he called "fairy rings") had diameters of 40 yards or more.
Within those 17th-century circles, Plot observed (as people also find today) soil dehydration and white sulphurous residue. He recorded that, in successive years, farmers enjoyed increased crop yields within the area of crop formations. The
Oxford professor (this is a PDF link) concluded the phenomenon could be caused by lightening. (Lightening is known to increase the levels of nitrogen in soil.) His colleagues seemed to agree, and the matter was closed.
For them, that is. But not for many people today.