About 71% of the Earth is covered by oceans. That equates to about 320.3 billion cubic miles of water. That's a lot of water. So it's not surprising that the oceans hide countless mysteries and wonders. Some of them are more amazing than others.

10. City of Alexandria

One of the greatest cities of antiquity was Alexandria, the famous metropolis founded by Alexander the Great himself. It was the third largest city in Egypt and was founded in 331 BC. It was home to the legendary Lighthouse of Alexandria and for more than 1,000 years was one of the greatest cities in the world, even though it was plundered in 641 AD. Then, like almost anything with such a history, its time essentially came to an end. Much of Alexandria's harbor disappeared into the sea for generations and has not been rediscovered for many years.

In the 1990s, divers began excavating the area and found amazing structures underwater, as well as incredible statues and artifacts. This included what may have been the royal residence of Cleopatra herself.

9. Plutonium

Make a list of things you may not want to just look for, the plutonium has to be in there somewhere. Plutonium is one of the most radioactive substances in the universe, and it emits dangerous alpha radiation. Outside of your body, relatively speaking, alpha radiation is not actually that dangerous. However, if you inhale it, the damage it causes inside your body can be catastrophic. It can cause chromosomal damage up to 1,000 times worse than other types of radiation. Given the potential harm, you need to make sure you know where the plutonium is and keep it secret. But that's hard to do when it's at the bottom of the ocean. Almost all of the plutonium you've heard of is man-made. It's a form of nuclear waste. But the plutonium in the ocean was probably formed when a star exploded and launched that material into space. It probably crashed on Earth millions of years ago and sank into the sediments of the ocean floor.

Plutonium born in a star is a rare treat for scientists. Natural elements like this unlock the keys to the universe in a variety of ways. We know that hydrogen and helium were formed when the universe was formed, but something like plutonium is almost unheard of.

8. Worm Highway

When and where life developed and evolved has always been a matter of interest to scientists, and it has been difficult to piece together. Figuring out what happened hundreds of millions of years ago is no easy task when all you have to do is go through rock samples. That's what makes the discovery of a series of worm tunnels so interesting. Researchers in Canada have discovered a very small tunnel in the rock that they have decided to call a superhighway that dates back to a time before dinosaurs appeared. The small tunnels were preserved in the rock, suggesting a bustling seafloor for the past 270 million years.

Although located at the bottom of a dark ocean, the fossils reveal a network of small tunnels, some as small as 0.5 mm in diameter, once home to worms that were busy living and being hunted by predators in the ocean. The depths of the ancient ocean that covers the area. Before this discovery, the idea of life existing in that place and at that time, especially with this diversity, was almost unheard of.

7. Ice Fingers of Death

Death Ice Fingers, which is the name of a Nordic death metal band, is not necessarily harmless if unusual natural phenomena. Nevertheless, with a name like that, there is no doubt that they are very interesting, albeit very rare. So what are death ice fingers? It's an underwater icicle.

Dead ice fingers are rarely observed because they do not last long. They are located in polar water beneath the ice and form long, curved columns of flowing ice. Because sea ice is made from salt water, the salt is squeezed out when fresh water freezes and forms channels in the ice. Sometimes, extremely salty unfrozen water remains in the ice and flows all the way to the ocean below. When it drains into the ocean, it sinks because its salt content is much higher than that of the surrounding seawater. But it is also well below freezing. As it sinks, the relative fresh water it encounters on its way down freezes when the two waters come into contact with each other.

It is possible for icicles to grow from the surface ice all the way to the bottom of the sea and then spread out from there. However, they are short-lived, as changing currents and temperatures can quickly destroy them.

6. Atlantis Japan

If you have never heard of the Monument of Wakana, you are not alone. Sometimes referred to as Atlantis, Japan. This site near the Ryukyu Islands in Japan has been a controversial discovery for many years.

Some believe the site shows evidence of an ancient civilization, perhaps even the lost continent of Mu. Initial speculation claimed that the pyramids found at the site could be 10,000 years old, a figure that was later revised to 2,000 or 3,000 years. Nonetheless, this would be a remarkable find, as pyramids of any type off the coast of Japan are certainly unprecedented. The problem is that perhaps they still are. One of the biggest mysteries surrounding the Monument of Nahuku is whether it is anything at all. Although the centerpiece of interest looks like a beautifully carved stepped pyramid, there is also plenty of evidence to suggest that it is simply a natural phenomenon. As you may know, certain types of stones can form angles in platforms and plates that make them appear to be carved into the corners. This has been observed in many other parts of the world. Some researchers believe this is the case with the sandstone in that country.

The biggest problem is that few people are interested in studying one way or the other, and the government has decided that the site doesn't make any sense.

5 feet

For nearly 15 years, Canada's West Coast has been plagued by one of the most morbid problems imaginable. Feet are constantly washing up from the sea. Intermittent human feet, always wearing shoes, appear on beaches up and down the coast. This has happened a dozen times, and not a single foot has appeared in pairs.

Some parts of the human body are easier to identify than others, but the feet are not particularly easy to determine. This has always been the case, especially when no one has been reported missing. After a few occurrences, rumors began to swirl like an ocean full of feet, and there was concern that there might be a serial killer out there chopping off feet and throwing them into the water. After much research and investigation, law enforcement was able to determine that 3 of the 4.5 meters had been washed away. We've said before that no matching pairs appeared, but that doesn't mean there weren't matching pairs after all. In fact, a pair of feet were found five years apart. The same one was found only after a long time.

So what happened? Accident. All of the identified parts belonged to people known to have died in the accident. The body fell into the water because a person's ankle is a relatively weak part that separates from the whole. And because it is in a shoe, it remains relatively safe from marine predators and other factors that could cause disintegration. Instead, they simply churn in the currents, sometimes for years, until they reach shore. the boot found in 2009 belonged to a man who disappeared in 1985.

4. Submarine rivers

In most cases, the river is not that magical. Sure, there have to be the longest rivers in the world, or even the oldest ones. But they are still rivers. We've all seen a river. But have you ever seen one at the bottom of the ocean? Because there are many of them, and they're pretty amazing.

The idea of a river in the ocean sounds a bit strange. Off the coast of California, you'll find the Monterey Canyon. A 320 km long river curves and meanders like any surface river, with huge samples crossing the sea floor. The Black Sea underwater river flows at a speed of about 6.4 kilometers per hour and stretches for 59 kilometers. Submarine rivers remain relatively unknown and generally understudied. They did not really exist until the 1980s. You can imagine it's hard to pick them out because they're just water that flows through more water. But they do flow like surface rivers and cut the same geological patterns in the submerged rock as surface rivers.

Rivers begin as sediment flows, such as avalanches and mudslides, but are able to move large amounts of sediment in a relatively short period of time at incredible speeds.

3. 9000 years of hunting the blind

Is this a fraud because it is not technically an ocean? Maybe, but it's still cool. Deep in the icy waters of Lake Huron, scientists have found evidence of humans hunting the blind 9,000 years ago. Artifacts and man-made stone structures have been found preserved in the pristine waters, proving that the world looked much different in one era than it does today. Back then, there was a land bridge in that part of the world because the lake level was hundreds of feet lower than it is today. And because the bridge was a relatively narrow path, it was an ideal place to hunt animals migrating from the north.

Archaeologists have discovered stone threads that could have been used to hold animals in captivity. In the wild, animals like caribou are naturally reluctant to cross anything if they don't have to. Even making a small stone wall, they would walk around it rather than over it.

These stone walls lead to the camp, where old tools, etc. were found. Things were so well preserved that there were still coals in the fire ring.

2. The Great Pacific Garbage Patch

Most of us have heard of marine litter belts before, but understanding their scale is another matter entirely. The effort to eliminate single-use plastics is directly related to the trash in our oceans, and we need to do something about it. Unfortunately, it's an uphill battle, as witnessed by the ridicule and strong opposition when people tried to trade plastic straws for paper a few years ago. You'd think people's livelihoods were being taken away from them.

So why is it such a big deal? The Great Pacific Garbage Patch is the largest of the five large garbage dumps at sea, covering 1.6 million square kilometers. It's twice the size of Texas and is made almost entirely of discarded plastic. How much plastic? About 1.8 trillion pieces weighing about 800,000 tons. Both of these figures are concentrated in the densest part of the patch, which means it is probably much higher in both.

Most of the plastics in the picture are so-called microplastics, tiny beads of plastic that are barely visible to the naked eye. However, some pieces are so large that they are dangerous to marine life in terms of simply trapping them, for example in nets. But smaller fragments are also dangerous because they are ingested by fish and then by humans.

1. The earliest life on Earth

Of all the things found in the ocean, few are as remarkable as some of the extremely old, tiny fossils found in Quebec, Canada. These fossils appear to be the oldest evidence of life found on Earth.

Fossils unearthed in iron-bearing sedimentary rocks show that they were once around hydrothermal vents dating back much further than you think anyone has ever found life before. Remember, humans didn't appear until about 300,000 years ago. Dinosaurs didn't appear until about 230 million years ago. But these fossils go back 3.7 to 4.2 billion years. The entire planet is only about 4.5 billion years old.

Life is by no means complex, and this is just the fossilized remains of microbial life, but the age suggests that the Earth got the biosphere rolling relatively quickly.