Since appearing in the media in the 1970s, crop circles have become the subject of speculation by various paranormal, ufological, and anomalistic investigators ranging from proposals that they were created by bizarre meteorological phenomena to messages from extraterrestrial beings.
Many crop circles have been found near ancient sites such as Stonehenge, a prehistoric monument located in the English county of Wiltshire. They have also been found near mounds of earth and stones raised over a grave or graves, also known as tumuli barrows, or barrows and chalk horses, or trenches dug and filled with rubble made from brighter material than the natural bedrock, often chalk. There has also been speculation that crop circles have a relation to ley lines.
Many New Age groups incorporate crop circles into their belief systems.
Some have related crop circles to the Gaia hypothesis, alleging that "Gaia", the earth, is actually alive and that crop circles are messages or responses to stimuli such as global warming and human pollution. It asserts that the earth may be modeled as if a single super-organism, in that earthly components (e.g. biota, climate, temperature, sunlight, etc.) influence each other and are organized to function and develop as a whole.
The main criticism of alleged non-human creation of crop circles is that while evidence of these origins, besides eyewitness testimonies, is essentially absent, some are definitely known to be the work of human pranksters and others can be adequately explained as such. There have been cases in which researchers declared crop circles to be "the real thing", only to be confronted with the people who created the circle and documented the fraud.
In his 1997 book The Demon-Haunted World: Science as a Candle in the Dark, Carl Sagan discussed alien-based theories of crop circle formation. Sagan concluded that no empirical evidence existed to link UFOs with crop circles.
Many others have demonstrated how complex crop circles can be created. Scientific American published an article by Matt Ridley, who started making crop circles in northern England in 1991.
He wrote about how easy it is to develop techniques using simple tools that can easily fool later observers. He reported on "expert" sources such as the Wall Street Journal who had been easily fooled and mused about why people want to believe supernatural explanations for phenomena that are not yet explained. Methods of creating a crop circle are now well documented on the Internet.
Among others, paranormal enthusiasts, ufologists, and anomalistic investigators have offered hypothetical explanations that have been criticized as pseudoscientific by skeptical groups like the Committee for Skeptical Inquiry.
Responding to local beliefs that "extraterrestrial beings" in UFOs were responsible for crop circles appearing in Indonesia, the government and the National Aeronautics and Space Agency (Lapan) described them as "man-made". Thomas Djamaluddin, research professor of astronomy and astrophysics at Lapan stated: "We have come to agree that this 'thing' cannot be scientifically proven. Scientists have put UFOs in the category of pseudoscience."
Signs indicate that some form of non-human intelligence is communication with us ... What's the message?
Academy Award nominated documentary filmmaker William Gazecki (Waco: "Rules of Engagement") offers a compelling and provocative look at the mysterious phenomenon of Crop Circles. Full of never-before-seen footage and interviews with leading Crop Circle researchers and scientists, Crop "Circles: Quest For Truth is a fascinating, in-depth exploration of prevailing theories about the origin and nature of Crop Circles and the possible implications for us and Planet Earth. An astonishing experience guaranteed to shift perspectives and alter perceptions of what is real.