Underwater explorers have been left baffled by mysterious holes punctured deep into the sea floor.
The “perfectly aligned” markings appear 1.6 miles beneath the ocean’s surface in rarely explored territory.
A yet-to-be spotted animal might be behind the formations but, with no sure answer, aliens have cropped up as a possible explanation.
The holes form a straight line and repeat at equal distances from each other, with the small hollows surrounded by tiny mounds of sediment.
The researchers at the National Oceanic and Atmospheric Administration's (NOAA) playfully hinted that "something" other than humans might be behind the symmetrical holes — a remark that set social media users imaginations running wild.
Some queried whether alien life-forms might be behind the formations.
Speculating that it might have been caused by a UFO, Facebook user Mike Swole said: “[You] might end up stumbling upon an underwater base with extra-terrestrial biological entities while down there.
“Won't be the first time one has been talked about or discovered.”
Slightly tongue-in-cheek, Nyron Alden posted: "I'm not saying that it's aliens, but it's aliens."
Other out-there suggestions included cartwheeling starfish and an aircraft shooting into the water.
Some came up with more mundane rationales behind the linear holes, including a dug-up whale spine or cabling that had since been pulled up.
The strange phenomena were spotted by the crew of the NOAA Okeanos Explorer vessel as they investigated the Mid-Atlantic Ridge.
The area is a mostly-unexplored region of the seafloor that is part of the world's largest mountain range, measuring an incredible 10,000 miles.
This latest sighting is not the first time the holes have been spotted in the area, according to the website Live Science.
It reported how two marine scientists from the US National Marine Fisheries Service also spotted mysterious hollows in the ocean floor during a dive in 2004.
"These holes have been previously reported from the region, but their origin remains a mystery," the NOAA researchers wrote on Facebook.
"While they look almost human made, the little piles of sediment around the holes make them seem like they were excavated by... something."
In 2004, scientists proposed that some kind of sea creature or organism possibly living in or sifting through the seafloor's sediment made the holes.
But, because no one has seen the mystery creatures that might be behind the markings, their exact origins remain unknown.
Researchers explored the region from May to September as part of the Voyage to the Ridge 2022 expedition.
The trip aimed to increase understanding of the North Atlantic’s underwater formation, including learning more about the deep-sea species in the area and how the frequent earthquakes in the sea are sparked.
