"Dark oxygen" is being produced deep in the ocean, and scientists are baffled by the strange phenomenon, according to a new study.

In science class, kids learn that plants need sunlight to do photosynthesis and create the oxygen we breathe. But, oxygen is being produced on the abyssal seafloor, which is so deep that sunlight cannot reach it, according to a study published on Monday in the journal Nature Geoscience.

Not only is oxygen being produced, but plants aren't creating it.

Instead of green, photosynthesizing plants, the oxygen is created by metallic “nodules” that look like lumps of coal. But, instead of heating a grill, they’re splitting H2O (water) molecules into hydrogen and oxygen.

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Faulty readings

The phenomena was first observed in 2013, when the lead scientist of the study, Andrew Sweetman, a professor at the Scottish Association for Marine Science, was studying the Clarion-Clipperton Zone, an area between Mexico and Hawaii. He believed his equipment was faulty when it showed that oxygen was being made on the dark sea floor, reports CNN.

“I basically told my students, just put the sensors back in the box," Sweetman, who also leads the institution’s seafloor ecology and biogeochemistry group, told CNN. "We’ll ship them back to the manufacturer and get them tested because they’re just giving us gibberish. And every single time the manufacturer came back: ‘They’re working. They’re calibrated.’”

Sweetwater ignored the readings because he'd only been taught that you can only get oxygen from photosynthesis, according to the BBC.

“Eventually, I realized that for years I’d been ignoring this potentially huge discovery,” Sweetman told BBC News.

What produces the ocean's oxygen?

Around half of the Earth's oxygen comes from the ocean, states the National Oceanic and Atmospheric Administration, NOAA.

Scientists attributed the production to the following:

• Oceanic plankton
• Drifting plants
• Algae
• Some bacteria

All the organisms listed are capable of photosynthesis, thus creating oxygen. But they wouldn't be able to do that so deep underwater.

Mining companies want to collect oxygen-producing modules

The modules, which form over millions of years, are made of ingredients needed to create batteries: lithium, cobalt and copper, according to the BBC. And mining companies are interested in collecting them.

However, Sweetman's new study raises concerns about the risks involved in collecting these deep-sea minerals.