They're not underwater craters, and they're definitely not from aliens. That's according to Danish scientists who say they've finally figured what's causing ocean-floor crop circles known as fairy rings.
According to LiveScience, these mysterious circles were noticed off the coast of Denmark. The unusual dark rings are basically circles of grass around a patch of dirt. (Via LiveScience)
Tourists in Denmark first took pictures of the rings back in 2008. The International Business Times points out many on the Internet started trying to come up with explanations for why they were there after pictures surfaced.
Scientists previously found the material forming a circle was eelgrass, but two scientists from the University of Southern Denmark and the University of Copenhagen took it upon themselves to get an answer to the mystery of why the grass made circle shapes.
Turns out the answer isn't nearly as exciting as alien landing sites and World War II bomb craters like some skeptics had reportedly thought. The scientists found the phenomenon is caused by something else that's already within the water.
In a statement, the scientists explained: "We have studied the mud that accumulates among the eelgrass plants and we can see that the mud contains a substance that is toxic to eelgrass."
They add that when the eelgrass dies, it begins withering away from the center of a grass patch, and that ends up creating those circles.
The scientists say the seagrass is also found in other parts of the world, but add researchers are working to make sure they don't disappear in the future from possible threats to its marine life.