Oceans cover nearly three quarters of our planet, but very little of what lies under the water’s surface is explored or well understood. Here are a few fascinating facts about this vital ecosystem that will make you appreciate our blue planet even more.

Woman swimming in the ocean, shot from above
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1. There’s really only one ocean, not seven

While ancient and modern cultures divided and named the seas of the known world, there’s technically only one global ocean.

The Arctic, Atlantic, Pacific, Indian and Southern basins all exchange water via currents that move around the entire Earth.

This means that changes in one region can affect the others.

Coral reef surrounded by brightly colored fish
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2. Most of Earth’s life is aquatic

Scientists estimate that up to 80% of the planet’s life is found under the surface of the ocean.

But we only know a small fraction of that mind-boggling biodiversity.

According to the World Register of Marine Species, there are about 250,000 accepted marine species. But that number that may represent less than 10% of the species that exist —  new marine life is being discovered everyday.

Hydrothermal vents on the ocean floor
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3. The hottest water is at the bottom of the ocean

Amid the chilly depths, hydrothermal vents release water heated up to a scalding 750º Fahrenheit (400º Celsius).

These deep-ocean hot springs are surrounded by chemically distinct ecosystems where exotic microbial communities have evolved. These communities thrive despite the high temperatures, the crushing pressure of the water and the absolute darkness.

Microscopic image of calcareous phytoplankton
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4. The sea produces most of our oxygen

Trees usually get most of the credit.

But the truth is that the majority of the oxygen in our atmosphere comes from marine plants.

Phytoplankton — tiny photosynthetic organisms that live in the sea — alone are responsible for half of the oxygen on Earth.

That's more than all the world’s tropical rainforests put together.

Humpback whale playfully swimming underwater in clear blue ocean
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5. The ocean bottom is a very noisy place

We may imagine the deep ocean as a silent space, yet scientists who’ve listened in say there’s almost constant noise. Because water particles are much more densely packed than air, sound travels faster and farther. The deep-sea cacophony includes the rumble of faraway earthquakes, melodies from moaning whales, snapping shrimp and wave-churning typhoons. In recent years, human-made sounds are increasing and negatively affecting marine animals worldwide.

Beautiful coastal scenery in Iceland
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6. The planet’s longest mountain chain is underwater

The largest geological feature on Earth is the Mid-Ocean Ridge, a continuous range of underwater volcanoes that stretches around the globe for 40,389 miles — nearly 10 times longer than the Andes.

Iceland, formed when volcanoes erupted millions of years ago, is one of the few places where you can stay dry while standing atop the ridge.

Aerial shot of glacier in Torres Del Paine National Park, Chile
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7. If the world’s ice melted, the sea level would rise 21 stories

The National Snow & Ice Data Center estimates that, if all the world’s ice sheets, ice caps and glaciers melted, the sea level would rise 230 feet – roughly the height of a 21-story building. Currently, ice melt and thermal expansion are causing sea levels to climb at a yearly rate of about one-eighth of an inch (3.2 mm) — a pace that continues to accelerate.