'Blue Planet II' producers discovered life where we didn’t know it could exist — here's what that was like

While the "Blue Planet II" team was exploring the Mariana Trench, they managed to film an ethereal snailfish approximately 5,000 meters underwater.
No one knew before then that creatures as complex as fish could live in water that deep, surrounded by so much pressure.
"The deep is always going to surprise us," said the episode's producer.

The most otherworldly and alien parts of the ocean are in the depths — the Mariana Trench could easily bury Mount Everest.

There's no light when you get into the hadal zone, the deepest part of the ocean. And as narrator Sir David Attenborough says in "The Deep," episode two of the BBC natural history documentary series "Blue Planet II," the pressure at the bottom is equivalent to the force of having 50 jumbo jets stacked on top of one another. Several sea slugs and starfish are somehow able to withstand the pressure, but few creatures can survive down there.

But as the "Blue Planet II" team was filming the episode, they discovered something they'd never expected to see: a fish. Using a remote camera, they captured footage of an ethereal snailfish, a translucent creature slowly swimming through the deep water.

"It's extraordinary" that such a complex animal could exist down there, Orla Doherty, the producer of the episode, told Business Insider. "I feel like we've pushed the boundary of what we know about the ocean just that little bit more."

While filming the series, the team spent more than 6,000 hours underwater over four years, visiting 39 countries on 125 expeditions. At least 12 of the discoveries made throughout the filming are being written up in new academic papers.

"As filmmakers, it has been unbelievably exciting to make these films in collaboration and true unity with the scientists who can unlock the secrets to this magical world," said Doherty.

They captured the footage of the snailfish at approximately 8,000 meters down, almost five miles underwater. It was the deepest a fish had been spotted until another team filmed a Mariana snailfish just recently 8,178 meters deep.

According to Doherty, there are probably many more surprises awaiting us down below.

"The deep is the final frontier for discovery here on this planet and there's stuff going on down there that makes you believe you've gone to another planet," she said. "The deep is always going to surprise us."

"Blue Planet II" airs on Saturdays at 9 pm ET on BBC America.