As a traveler, oceans were a kind of measuring stick—

If I crossed one by plane, my trip was farther and thus felt more exciting (and hurt my budget that much more).

But, I didn’t know much about that big blue presence that separated me from exotic locations, not really.

So, let’s learn together, shall we?

Taken by M. Hardy via [Public Domain].

Here are answers to some frequently asked questions about oceans:

How many oceans are there?

Historically, there are four oceans, the Pacific Ocean, Atlantic Ocean, Indian Ocean, and the Arctic Ocean. These are the oceans as recognized by most countries, and this is what I was taught via the good ol’ NYC Board of Education.


Today, there are five oceans. Most countries and educational bodies now agree on a 5-ocean model, one that includes the Antarctic Southern Ocean as the fifth one. There is some debate still as to the boundaries of the Southern Ocean. In the US, though, it is the portion below latitude 60° S.

However, again—

Technically speaking, there is only one ocean. The world ocean, or global ocean, is all the oceans combined. This kinda makes sense when you look at a globe or world map, as they’re all connected.

How deep is the ocean?

The average depth of the entire world ocean is 3,688 m (around 12,100 ft, or 2.3 miles). The deepest part is located in the Mariana Trench of the western Pacific Ocean, specifically a spot called Challenger Deep.

Challenger Deep is around 11 km (36,200 ft, or almost 7 mi) down. It is named after the crew of the HMS Challenger.

Here’s the average depth of each ocean separately:

  1. Pacific Ocean – 3,970 m (13,025 ft)
  2. Indian Ocean – 3,741 m (12,274 ft)
  3. Atlantic Ocean – 3,646 m (11,962 ft)
  4. Southern Ocean – 3,270 m (10,728 ft)
  5. Arctic Ocean – 1,205 m (3,953 ft)

How much of the ocean has been explored?

This is a more complicated question, as it could mean three things: exploration of the ocean surface (undiscovered islands and whatnot), the sea floor, or the ocean between the surface and the ocean floor (like what marine life exists there).

Schmidt Ocean Institute says we’ve only mapped 5% of the ocean floor. Given the fact that the ocean is around 71% of the earth’s surface, this means we’ve only mapped about 66% of the world.

Also, what we’ve mapped is usually the parts of the ocean floor nearest the coastlines, as, well, it’s just easier. Scientists have even completely mapped the planet Mercury and just about all of Venus and Mars, but not close to done on our own oceans!

Which ocean is the largest?

The Pacific Ocean is the largest ocean on earth, covering more than 1/3 of the entire surface of the earth.

Here’s a quick breakdown of the oceans by surface size:

  1. Pacific Ocean – 168,123,000 km² (65,144,000 mi²)
  2. Atlantic Ocean – 85,133,000 km² (32,870,000 mi²)
  3. Indian Ocean – 70,560,000 km² (27,243,000 mi²)
  4. Southern Ocean – 21,960,000 km² (8,479,000 mi²)
  5. Arctic Ocean – 15,558,000 km² (6,007,000 mi²)

The world ocean (all of the above combined) is 361,934,000 km² (139,743,000 mi²).

Now, here’s a breakdown of the oceans by water volume:

  1. Pacific Ocean – 669,880,000 km³ (160,713,000 mi³)
  2. Atlantic Ocean – 310,411,000 km³ (74,472,000 mi³)
  3. Indian Ocean – 264,000,000 km³ (63,337,000 mi³)
  4. Southern Ocean – 71,800,000 km³ (17,226,000 mi³)
  5. Arctic Ocean – 18,750,000 km³ (4,498,000 mi³)

The world ocean (all of the above combined) is about 1,335,000,000 km³ (320,284,000 mi³) in cubic water volume.

Where do the Atlantic and Pacific meet?

The Atlantic and Pacific Oceans meet at an imaginary line drawn from Cape Horn in South America straight down to Antarctica.

Cape Horn is the southernmost point of the Tierra del Fuego archipelago in southern Chile, located on Hornos Island.

How much of the earth is ocean?

About 71% of the world is covered by saltwater oceans. Those oceans make up around 97% of the entirety of Earth’s water, according to the National Ocean Service. Less than 1% of all the Earth’s water is fresh.

What is the difference between an ocean and a sea?

In geography, the oceans are the five major bodies of water, while seas are often located where oceans meet land, usually surrounded on most sides by land. A sea is often partially or fully enclosed by land. Depth, area, and marine life also determine which is a sea and which is an ocean.

More Ocean Facts to Ponder

Here are a few more ocean facts to consider:

Filmmaker James Cameron, in 2012, made the first solo sub dive to the Mariana Trench spot Challenger Deep. It took his submarine 2 hours and 36 minutes to sink down to the bottom.

The 8th of June is considered World Oceans Day.

There are underwater lakes and rivers in the ocean! Underwater lakes and rivers form when seawater seeps through salt and increases in density. Since it is denser than the water around it, it flows differently than that other water, so scientists term these as lakes and rivers, just as on land.

Scientists estimate that 80% of Earth’s species live on land, 15% exist in the world ocean, and 5% in freshwater.

The underwater Mid-Ocean Ridge (MOR) is the longest mountain range on Earth. It stretches for around 65,000 km (40,400 mi), and it’s total length is 80,000 km (49,700 mi) long.

Scientists estimate that around 91% of all marine species are yet to be classified or discovered.

Most (70%) of the oxygen in the atmosphere and vital for our breathing is produced by marine and ocean plants, such as plankton and kelp.

So, what did you think? Got any more cool facts about oceans to add? Leave a comment and let’s chat!


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