1. About two-thirds of all marine life remain unidentified. Most are probably tiny ocean bugs or whatever. 2. No one knows what made this sound. pmel.noaa.gov While the most famous mystery underwater sound — the Bloop — is consistent with (read: probably) some underwater icequake or another, no one knows for sure what made this sound, nicknamed Julia. So it might be Cthulhu. You don't know. 3. There are probably halibut bigger than this, which broke world records at 515 pounds. i.imgur.com Caught by a German dude in Norway. 4. We might not have identified eight whale and dolphin species. tampabay.com Source. 5. About 90% of the ocean is still unmapped. libero-magazin.de And it could take 125 years to get that done. (Source.) 6. Because 95% of it we haven't explored, meaning there COULD be mermaids. bestdivingingreece.com You don't know! Stop pretending like you know! (Source.) 7. Mysterious rivers and lakes exist underwater, with creatures found nowhere else. tumblr.com Some of these brine-filled rivers and lakes have mussels living around them, and some don't. Why don't some have mussels? Why? (Brine is super salty and way more dense than water, so it sinks and forms these pools and streams. SCIENCE.) 8. There are likely more new deep-sea shark species than even this fishing expedition turned up with last year. Behold: the ghost shark. 9. How much fish would a fishery fish if a fishery could fish deep-sea marine habitats? lunar.thegamez.net We're not really sure how deep-sea fishing affects the ecosystem due to a lack of data. So maybe we'll be eating ghost shark in 50 years because it tastes like rainbows, or maybe catching a lot of ghost shark would be super bad for the ocean. 10. Somebody just south of New Zealand caught this 39-foot-long Colossal Squid, but we don't know a lot about it. fish.govt.nz It's sort of hard to observe something that dives up to 6,500 feet below the surface. 11. In the Triassic period, the Kraken may have eaten bus-sized Ichthyosaurs. i.livescience.com Yes, a giant, murderous squid-like creature is the supsect behind a pile of Ichthyosaur bones found in the Nevada desert. And -- to add a dose of CREEPY -- the bones look like they were ARRANGED. The Kraken either drowned or broke the necks of its victims, and then PLACED them in an alternating double-line pattern like suckers on a tentacle.In summation: scientists hypothesize that a giant sea monster killed other giant sea monsters and made self-portraits with their lifeless bodies. 12. We know about seven underwater waterfalls, but there could be more. blog.makemytrip.com In the sea between Greenland and Iceland, where some frigid water mixes with less frigid water, lies what is technically Earth's largest known waterfall: 175 million cubic feet of water per second (2,000x Niagra Falls) dropping 11,500 feet (3x the height of Venezuela's Angel Falls, above). (Source). 13. It's also unclear how many valuable minerals are hiding out in the water. wpmedia.business.financialpost.com There's gold in them submarine hills, y'all. 14. Off the coast of Cuba, some researchers discovered a possible lost city..? It could be nature playing tricks, or it could be that long-lost Mayan city that disappeared under the waves. CoughATLANTIScough. 15. And no one's entirely sure what this rock structure is doing here. media.gizmodo.co.uk Aliens. 16. But the biggest unknown is how to go about studying the ocean, when most of it doesn't really want to be found. We need a bunch of submarines that can take some serious pressure and shit. 17. Respect the sea, guys. Tap to play or pause GIF Tap to play or pause GIF Tap to play or pause GIF Tap to play or pause GIF tumblr.com Because we don't know what's in it.