“How inappropriate to call this planet Earth when it is quite clearly Ocean.” –Arthur C. Clarke

It’s a profound thing to consider: 70 percent of the the planet’s surface is covered in the continuous body of saltwater known as the ocean. What we know of as “earth” is really just the tall spots that the ocean can’t subsume. (Yet.) We think the continents are king, but they are just islands in a much greater habitat.

While the ocean dominates the planet, humankind is doing a pretty good job of messing things up for it. Overfishing, climate change, and reckless pollution are wreaking havoc on the ocean’s organisms. Thankfully, the sea is so deep and so vast – and we seem for fixated on exploring above than below – that at least some of its deepest parts may be spared our folly. And also thankfully, the ocean is starting to get some attention. If there has been one big story about the environment this year, it has been the enormity and devastation of plastic pollution in the ocean. With whole countries dedicated to getting rid of single-use plastics, hopefully we can stop this train before it crashes.

In the meantime, getting to know the ocean is a great way to start feeling more invested in protecting her. So without further ado, some facts:

1. There are many parts to the whole
The World Ocean is also collectively referred to “the sea,” but geographers divvy it up into four major parts: the Pacific, Atlantic, Indian, and Arctic. Smaller regions are referred to as bays, gulfs, and seas. Think of the Bay of Bengal, the Gulf of Mexico, and the Sea of Cortez. While the International Hydrographic Organization lists over 70 distinct bodies of water called seas, the Caspian Sea (and the Great Salt Lake) are saltwater bodies that stand apart from the world’s oceans.

2. It has a lot of water!
Not to state the obvious or anything, but we’re talking a lot of water. The ocean contains some 320 million cubic miles (1.35 billion cubic kilometers) of water; or around 97 percent of Earth’s water supply. Unfortunately for thirsty people everywhere, that water is about 3.5 percent salt. Though that is good news for the ocean because it means we’re not trying to steal it all.

3. It is really, really, really deep
Like, really. Almost half of the ocean is more than 9,800 feet (3,000 meters) deep. The lowest spot in the ocean, and thus the planet, is the Mariana Trench in the western Pacific Ocean. It reaches down about 36,200 feet, nearly 7 miles, below sea level.

4. It contains the longest mountain chain in the world
The Mid-Oceanic Ridge is a mountain chain that wraps around the globe for a stunning 40,390 miles (65,000 kilometers). NOAA points out this profound nugget: “Like the rest of the deep-ocean floor, we have explored less of the mountains of the Mid-Ocean Ridge system than the surface of Venus, Mars, or the dark side of the Moon.”

5. It is home to the world’s largest living structure
The glorious Great Barrier Reef stretches for more than 1,400 miles off Australia’s northeastern coast; it is one of the seven wonders of the natural world, and no wonder, so to speak. It is larger than the Great Wall of China and the only living thing on Earth that can be seen from space. Hopefully, we humans will get our act together and do something about climate change because it is quickly wiping this wonderful structure out.

6. It has its own lakes and rivers
Of course it does, because it’s the ocean and can do whatever it wants. NOAA explains that lakes and rivers form deep in the sea when seawater seeps up through thick layers of salt, which are present beneath the seafloor. “As the water seeps up, it dissolves the salt layer, causing it to collapse and form depressions. The dissolved salt makes the water denser, and because it is denser than the water around it, it will settle into the depressions, forming a river or lake.” They can be small or large, sometimes as long as a few miles – and just like our rivers and lakes, they have shorelines and even waves. You can see images in the video below.

7. It’s a life saver … or giver
About 70 percent of the oxygen we breathe is produced by the oceans. Thanks, oceans!

8. It has its own waterfalls
Because mermaids like water features too. The planet’s largest known waterfall is underwater in a stretch of ocean between Greenland and Iceland. How does that work? Known as the Denmark Strait cataract, the underwater waterfall has a jaw-dropping drop of 11,500 feet (3,505 meters) with a volume of 175 million cubic feet (5.0 million cubic meters) of water. The phenomenon occurs because of the meeting of colder water and warmer water from either side of the strait. “When the colder, denser water from the East meets the warmer, lighter water from the West,” explains LiveScience, “the cold water flows down and underneath the warm water.”

9. It holds the world’s greatest collection of historical artifacts
The ocean plays host to a million shipwrecks, says director of NOAA’s Maritime Heritage Program, James Delgado. National Geographic reports that more historical artifacts make their watery home in the ocean than in all of the world’s museums combined.

10. It’s swimming with mysterious things
Scientists estimate that we have only classified 9 percent of the ocean’s species. You think octopuses are weird? They may be some of the more normal characters down there.

11. And we barely know it all
We know more about the moon’s surface than we do about the depths of the ocean. Consider this: 12 people have stepped foot on the moon … but only three have been to the Mariana Trench.

And now for a Public Service Announcement:

VIDEO: The blanket of trash on a creek that flows between the makeshift homes of a Manila slum is so dense it appears one could walk across it like a paved street pic.twitter.com/bdkH0LFcPJ

— AFP news agency (@AFP) June 5, 2018

Sources: National Geographic, NOAA, LiveScience.

This updated article was originally published in 2018.