A Vast Unknown
About 70 percent of the Earth's surface is covered with water, yet the oceans largely remain a mystery for scientists.
More is known about the moon's surface than the depths of the ocean. In fact, 12 people have stepped foot on the moon, but only three have been to the Mariana Trench — the deepest part of the ocean, at roughly 7 miles (11 kilometers) deep.
In celebration of World Oceans Day (June 8), here are a few of the most bizarre discoveries from the planet's oceans.
Mysterious life lurks there
Though 94 percent of life on Earth is aquatic, about two-thirds of all marine life remains unidentified. New species are constantly being discovered, raising more questions about marine life.
This year, the SUNY College of Environmental Science and Forestry's (ESF) annual list of the Top 10 New Species included a striking red species of sea dragon that remained undiscovered despite living in shallow waters off the western coast of Australia.
Spooky sounds from the deep
It's not just the flora and fauna of the oceans that remain mysterious to scientists; there are a handful of sounds from the depths of the oceans that scientists cannot explain with any certainty.
"The Bloop" may be the most famous underwater sound, captured in 1997 by hydrophones set out by the National Oceanic and Atmospheric Administration (NOAA). It is one of the loudest ocean sounds ever recorded, and while the noise is consistent with an underwater ice quake — a large iceberg fracturing — no one knows for sure what made the sound. [Listen to 6 Spooky Sounds from the Deep Sea]
Because the Bloop mimics marine animal sounds, many people have jokingly linked the noise to Cthulhu, a fictional part-octopus monster created by sci-fi writer H.P. Lovecraft in 1928. The Bloop's volume is too great to be made by any sea creatures known to science, but there are innumerable creatures still unknown.
Underwater lakes and rivers
Oceans have lakes, and rivers, that exist underwater. How?
When seawater seeps through thick layers of salt, the salt dissolves and forms depressions in the seafloor. NOAA explains that dissolved salt also makes the water in that area denser, and as such, it will settle into the depressions. These underwater lakes and rivers, also known as brine pools, are similar to their land-based counterparts — they have shorelines, and even waves.
There are even waterfalls in the ocean.
Technically, the Earth's largest known waterfall lies between Greenland and Iceland — underwater. In an article for Conde Nast Traveler, Jeopardy champ Ken Jennings wrote about the Denmark Strait cataract, an underwater waterfall with 175 million cubic feet (5.0 million cubic meters) of water dropping a whopping 11,500 feet (3,505 m).
The waterfall is formed by the temperature difference between the water on each side of the Denmark Strait. When the colder, denser water from the East meets the warmer, lighter water from the West, the cold water flows down and underneath the warm water.
The Denmark Strait cataract is more than three times the height of Angel Falls in Venezuela, which is considered Earth's highest aboveground uninterrupted waterfall. The Denmark Straight cataract carries almost 2,000 times the amount of water of Niagara Falls at peak flow, according to Jennings.
Corals wear sunscreen
Warmer oceans, more acidic waters, pollution and human interference are threatening marine life across the globe, scientists say.
Coral reefs contain some of the most delicate ocean residents. Yet coral has a way to naturally protect itself: "sunscreen." Over millions of years, corals in Australia's Great Barrier Reef developed protective barriers that help them survive in the sun, according to a statement by the Commonwealth Scientific and Industrial Research Organisation (CSIRO).
Scientists are already working to mimic the corals' natural sun protection. CSIRO scientists have worked with skin care company Larissa Bright Australia to create UVA/UVB sunscreen filters inspired by the corals' sunscreen code, the CSIRO statement noted.
The oceans are rich with more than just marine life.
Dissolved gold can be found in the water of all oceans, according to NOAA's National Ocean Service. But although the oceans hold nearly 20 million tons (18 million metric tons) of gold, it is so dilute that its concentration is on the order of parts per trillion.
There is, however, undissolved gold in and on the seafloor. Mining for this gold — located at least a mile or two underwater and encased in rock — may not be worthwhile, as there currently isn’t a cost-effective way to mine or extract gold from the ocean. NOAA estimates that if all of the gold were extracted from the world's oceans, each person on Earth could have 9 lbs. (4 kilograms) of the precious metal.
Historical artifacts abound
More historical artifacts lie in the ocean than in all of the world's museums combined, according to National Geographic.
Whether it's a Viking sundial used for navigation or a jadeite gift to ancient gods, a lot of the world's history can be found at the bottom of the seas. That's not to mention the vast number of shipwrecks lying on the ocean floor; one estimate by James Delgado, director of NOAA's Maritime Heritage Program, puts the number at 1 million, with the majority of the wrecks still undiscovered, according to an article in Popular Mechanics.
The ocean holds many secrets about human history and the planet's origins, scientists say.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.