Crop circles are areas of standing crops that have been flattened in the form of a circle or more complex pattern frequently associated with the extraterrestrial and have certainly been a long standing mystery. The most reasonable explanation may be that it is a hoax. How many people would believe UFOs are trying to send us messages? The hoax theory was made all the more believable for me when I read this:

“In 1991 two retired lanscape painters Englishmen, Doug Bower and Dave Chorley, proclaimed they were responsible for all the crop circles in England since 1978, starting as a joke to make people think UFOs were landing. They demonstrated their technique for the cameras with a 1.2-metre board attached to a rope they hung around their necks. One held one end of a string in the centre to determine the radius while the other held the other end and stomped down the plants with the board.”

-http://aliens.monstrous.com/circlemakers.htm

But then I came across a website with arguments against the hoax theories. And the one that stood out the most to me was the unexplainable changes to plants. Scientists studied the differences between the plants found inside the crop circles and the plants outside them, from the same field.