For the past year, a set of mysterious holes on the sea floor have stumped scientists.
Last summer on one of the dives during the 'Voyage to the Ridge' expedition, researchers came across a series of sublinear holes over a mile beneath the surface of the Atlantic Ocean.
At a glance, the identical looking trenches appear man made, with small piles of earth beside them.
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However, the crew of the Okeanos Explorer were unable to have a look inside to see where - if anywhere - they led.
Twelve months on, scientists have been unable to work out what they are.
"We observed several of these sublinear sets of holes in the sediment," a spokesperson for NOAA Ocean Exploration said.
"These holes have been previously reported from the region, but their origin remains a mystery.
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"While they look almost human-made, the little piles of sediment around the holes make them seem like they were excavated by ... something."
At the time, the NOAA posted some pictures of the holes to Facebook and Twitter, with people as baffled as them.
However, some offered suggestions as to what might have created them.
"I wonder if some company may be conducting sea floor samples," wrote one person.
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"That might explain the straight lines and the spacing of the holes. Especially if you have seen others in the region. Only thing is, everything else around it doesn't seem like it's been disturbed."
Another commented: "Upwelling! Freshwater from a land source bubbling up? As if there's a rock under there allowing the flowing water to break through in that linear manner."
It's not the first time these kinds of holes have been spotted, however.
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Back in 2004, a team of explorers ventured down over 2,000 meters along the Mid-Atlantic Ridge and discovered several similar indentations.
Writing in their paper, scientists Michael Vecchione and Odd Aksel Bergstad offered their own theory as to their origin.
They explained: "The holes were ca. 6 × 1.5 cm, with distance between holes similar to hole length.
"The holes that appeared to be most recently formed were each surrounded by raised sediment. Holes that appeared older were partly filled with sediment and the raised surrounding sediment was less obvious.
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"Overall, these lebensspuren created small-scale heterogeneity in the local soft-bottom benthic ecosystem.
"The source of the holes or how they were constructed is unknown, but the raised sediment may indicate excavation by an infaunal organism or digging and removal by e.g., a feeding appendage of a large epifaunal animal."
Topics: Science, World News, Weird