Only four species, the great white shark, tiger shark, bull shark, and the oceanic whitetip shark, are known to occasionally attack humans, yet even when humans swim alongside these fearsome-looking behemoths they rarely attack.
The tiny Australian box jellyfish is considered the most venomous animal in the sea—their sting can cause cardiac arrest, paralysis or death in humans in just a few minutes.
Killer Whales
But the true ruler of the sea is the killer whale. Killer whales are apex predators, which means they have no natural predators. They hunt in packs, much like wolves, which are also at the top of their food chain.
Jellyfish There's a place where you can swim with jellyfish without fear of being stung. It's appropriately called Jellyfish Lake and it's located in the Rock Islands of Palau. Here, the jellyfish have lost their stingers somewhere over the last 12,000 years, making it perfectly safe to jump in for a dip.
While thousands of climbers have successfully scaled Mount Everest, the highest point on Earth, only two people have descended to the planet's deepest point, the Challenger Deep in the Pacific Ocean's Mariana Trench.
The pressure from the water would push in on the person's body, causing any space that's filled with air to collapse. (The air would be compressed.) So, the lungs would collapse. At the same time, the pressure from the water would push water into the mouth, filling the lungs back up again with water instead of air.
But reaching the lowest part of the ocean? Only three people have ever done that, and one was a U.S. Navy submariner. In the Pacific Ocean, somewhere between Guam and the Philippines, lies the Marianas Trench, also known as the Mariana Trench.
Vescovo's trip to the Challenger Deep, at the southern end of the Pacific Ocean's Mariana Trench, back in May, was said to be the deepest manned sea dive ever recorded, at 10,927 meters (35,853 feet).
Hidden inside the Earth—within the first several hundred kilometers below the crust—there is another ocean. It is, most likely, the largest ocean in the world. This water is not sloshing around in a big pool.
More than 80 percent of the ocean has never been mapped, explored, or even seen by humans. A far greater percentage of the surfaces of the moon and the planet Mars has been mapped and studied than of our own ocean floor. Although there is much more to learn, oceanographers have already made some amazing discoveries.
But is anyone, apart from submarine crews, living under water now? The answer is - Yes: the aquanauts.
The Bajau Laut have been sea nomads for centuries. In the waters they call home around the Philippines, Malaysia, and Indonesia, they dive to incredible depths for pearls and for food, living off the sea like no other community on earth. They are among the world's best freedivers.
The stateless Bajau people, also known as 'sea nomads,' have literally lived at sea for over 1,000 years. For most of us, kicking back in a stilted chalet by the sea makes for picture-perfect holidays. But try living that way every day. For the stateless Bajau, living on the water is just daily routine.
Assuming you're in warm waters and wearing a wetsuit and life vest, you could potentially survive for as many as three to five days, at which point you'll most likely succumb to dehydration. That is, unless a shark gets you first.
In fact, most of the waters remain unexplored, uncharted and unseen by our eyes. It might be shocking to find out, but only 5% of the ocean has been explored and charted by humans. The rest, especially its depths, are still unknown.
The deepest part of the ocean is called the Challenger Deep and is located beneath the western Pacific Ocean in the southern end of the Mariana Trench, which runs several hundred kilometers southwest of the U.S. territorial island of Guam. Challenger Deep is approximately 10,935 meters (35,876 feet) deep.
Geologists know that there are two kinds of "lost cities" underwater: those that were made by humans, and those that weren't. The latter turns out to be the case for one such city, discovered by tourists diving off the Greek island of Zakynthos in 2014.
Paul Watson: The reality is that if the ocean dies, we die – because the ocean provides all of those things which make it possible for us to live on the planet. Over 70% of the oxygen is actually produced by phytoplankton in the ocean, and since the 1950 there's been a 40% diminishment in phytoplankton population.
Drinking seawater can be deadly to humans.
Seawater contains salt. When humans drink seawater, their cells are thus taking in water and salt. While humans can safely ingest small amounts of salt, the salt content in seawater is much higher than what can be processed by the human body.
The three most common organisms at the bottom of the Mariana Trench are xenophyophores, amphipods and small sea cucumbers (holothurians), Gallo said. "These are some of the deepest holothurians ever observed, and they were relatively abundant," Gallo said.
Although the only cities currently underwater are those that were submerged over time, plans for underwater cities of the future are already being considered. These plans are not as far-fetched as they sound, and some underwater restaurants and resorts already exist around the world.
Features of the ocean include the continental shelf, slope, and rise. The ocean floor is called the abyssal plain. Below the ocean floor, there are a few small deeper areas called ocean trenches. Features rising up from the ocean floor include seamounts, volcanic islands and the mid-oceanic ridges and rises.
Several mountains in Himalayan country Bhutan are believed to be unconquered, namely the world's largest unclimbed mountain: Gangkhar Puensum. Unexplored areas around the world also include small islands, such as Pitcairn Island off of New Zealand, and Palmerston Island in the South Pacific.