The mystery of crop circles is ongoing and no one knows definitely why they exist. Due to the exact precision of measurements, it would be impossible for humans to construct them. In the past few years it seems that some of them have contained some kind of message for us that is in code. It's speculated that it is a way the extra-terrestrials have to communicate with us. One of the most famous involves a possible answer to a message that was sent from Earth years earlier in an effort to communicate with other beings. The code was sent out in binary code, something related to computer code. It showed certain aspects of life on Earth, such as the image on the right.
The crop circle "answer" to this message came much later and showed life on another planet using the same categories as the original 1974 code sent from Arecibo Radio Telescope in Puerto Rico by SETI (Search for Extra-Terrestrial Intelligence). It appeared in a field in August 21, 2001 near the Chilbolton radio telescope in Hampshire, UK. There have been other interpretations of the geometric configurations of other crop circles as to messages that they might contain. It seems that these images (many of them not circles) are a way a more technologically advanced civilization is trying to communicate with us.
Recently there has been another theory put forward by Dr. Horace Drew that the messages are not even for us but are left by human time travelers as directional markers. It's as if they are saying "this is the day" and marking it. Dr. Drew speculates that these advanced beings are able to travel back in time by traveling between dimensions. He said, “So the trouble is we don’t know space time physics enough to understand what’s happening. It’s beyond our knowledge.” (The Sun). Dr. Drew has been studying crop circles now for over 20 years. It's an interesting idea and indeed, we don't know what the reason for crop circles.