What is the truth behind Crop Circles?

 

During the last few decades, crop circles have been appearing suddenly and especially at night in grain fields all over the earth.

It is reported, by some cerealogists, (people who study crop circles) that these diagrams must be created by intelligent alien beings from elsewhere. Also, it is believed that the aliens are very intelligent and much more advanced than we are (Humans). Moreover, it is reported that no one has ever seen those aliens doing those crops. Usually there aren't even any ufo sightings associated with the circles, except for those reported after the fact by people with overactive imaginations. Besides, it is known that Crop circle designs are constructed from circular arcs and straight lines. Finally, it is widespread that aliens have been defacing the earth's surface with geological graffiti for a very long time.