killer whale, the team behind "blue planet" 2 has gone to extreme to never before seen angle to see oscrcarritorial sharks. >> it's the awe-inspiring new series taking a deep dive into parts unknown. "blue planet 2" were able to explore the world beneath the ocean's surface like never before. new environments discovered. an under water lake of toxic brian and sulfur surrounded by flourishing eco system. >> the cure for cancer could lie here. in this b rine. >> what's different about this series. >> we've really tried to tell unbelievably surprising and new stories from the ocean. the ocean is such a giant, giant part of our planet is really unexplored. >> they spent four years on the project. >> we spent unprecedented 6,000 hours under water so never seen before behaviors and on top of that another thousand hours in deep sea submersibles exploring new worlds in the ocean's deep abyss. >> what was your favorite part. >> the day we filmed this volcanoe. went down to see something we weren't sure what we were going to see. it's like i went to another planet that day. and came back to earth to