How deep is the ocean?

The average depth is about 3.7 km. The deepest known point, the Challenger Deep in the Mariana Trench, is roughly 10,900–11,000 m deep, with figures varying slightly between surveys.

Why is the ocean blue?

Water absorbs red, orange and yellow light more strongly than blue, so blue light travels furthest and is scattered back to our eyes. Plankton, sediment and reflections of the sky can shift the colour towards green, grey or brown.

An underwater mountain, usually an extinct volcano, that rises from the seafloor without reaching the surface. Currents flowing around seamounts can bring up nutrients, making them hotspots for fish, sharks, turtles and whales.

How much of the ocean floor has been mapped?

The whole seafloor has been mapped at low resolution using satellites, but the Seabed 2030 project reported that only about a quarter had been mapped in detail by sonar in the early 2020s. The figure is rising each year.

Can I dive in the ocean in 3D in the app?

Yes. You start floating on the surface of the open Pacific and can dive down onto a seamount topped with a coral reef, swimming among fish schools, turtles, rays and whales in interactive 3D.

Blue water, sunken mountains and the dark depths below

Ocean & underwater

3D landscape · Open Pacific, over a seamount

Land here and explore →

The ocean covers about 71% of Earth's surface and holds roughly 97% of its water. Its average depth is around 3.7 km, and its deepest trenches reach almost 11 km below the waves. Sunlight fades within a few hundred metres, so most of the ocean's volume is permanently dark, cold and under immense pressure. In this app you can float on the surface of the open Pacific and then dive down onto a seamount whose summit is capped with a coral reef, past schools of fish, turtles, rays and whales.

The ocean drives Earth's weather and climate, absorbs much of the heat and carbon dioxide released by human activity, and its tiny drifting plants produce a large share of the oxygen we breathe. It is home to the largest animals that have ever lived. It is also under growing pressure from warming, acidification, overfishing and plastic pollution.

Key facts

Model setting: Open Pacific seamountA reef-capped underwater mountain far from land
Surface covered: About 71% of EarthThe Pacific alone covers roughly a third of the planet
Share of Earth's water: About 97%Almost all of it salty
Average depth: About 3.7 kmNOAA-cited estimate of roughly 3,682 m
Deepest point: Challenger DeepMariana Trench, roughly 10,900–11,000 m deep; estimates vary
Sunlight zone: Top ≈ 200 mWhere almost all photosynthesis takes place
Largest animal: Blue whaleUp to about 30 m long, the biggest animal known to have lived
Longest mountain range: Mid-ocean ridgeRoughly 65,000 km, almost all of it underwater
Seafloor mapped in detail: Roughly a quarterAs reported by Seabed 2030 in the early 2020s

The ocean's light zones

Oceanographers divide the open ocean into layers according to how much light reaches them. The sunlight zone, or epipelagic, runs from the surface to about 200 m. It is the only layer with enough light for photosynthesis, so it supports almost all ocean plant life and most familiar sea creatures. Below it lies the twilight zone, or mesopelagic, from about 200 to 1,000 m, where a faint blue glow still filters down by day but is far too weak for plants to grow.

Beneath 1,000 m begins the midnight zone, or bathypelagic, where no sunlight reaches at all and the only light comes from living things. Below about 4,000 m is the abyssal zone, cold and close to freezing, stretching across the vast flat plains of the deep seafloor. The deepest layer, the hadal zone, lies below about 6,000 m and exists only in trenches. Pressure rises by roughly one atmosphere for every 10 m of depth, so at the bottom of the deepest trench it is more than a thousand times greater than at the surface.

Living light

Most animals in the deep water column can make their own light, a talent called bioluminescence. They use it to find mates, lure prey and hide. One study off California found roughly three-quarters of the animals it observed were bioluminescent.

Why the sea is blue

Water is not perfectly clear. It absorbs the red, orange and yellow parts of sunlight more strongly than blue, while blue light travels furthest and is scattered back towards our eyes. In clear open ocean with little plankton or sediment, that gives the sea its deep blue colour. Coastal water often looks green or brown because of plankton and silt.

Divers notice this filtering quickly. Red fades within the first ten metres or so, followed by orange and yellow, so a red fish can look grey or black only a short way down. By a few tens of metres the world turns blue-green, and in very clear water faint blue light can be detected down to around 1,000 m. This is why many deep-sea animals are red or black: without red light, they are effectively invisible.

Seamounts: oases in the open ocean

Seamounts are underwater mountains, most of them extinct volcanoes, that rise high above the surrounding seafloor without breaking the surface. Estimates of how many exist vary widely: there may be tens of thousands taller than 1,000 m, and far more smaller ones. Flat-topped ones, called guyots, were planed off by waves before they sank. In warm, shallow water, a seamount's summit can be capped by a coral reef, as in the 3D scene in this app.

Seamounts are often biological hotspots. As currents flow around and over them, they can stir up nutrient-rich water from below and trap swirls of water above their peaks, feeding plankton and the animals that eat it. Tuna, sharks, rays, turtles and whales gather around them. That richness has also made some seamounts targets for intensive deep-water fishing.

Currents and upwelling

Surface currents are driven mainly by wind and steered by Earth's rotation. They form great circular gyres in each ocean basin, with fast currents such as the Gulf Stream carrying warm water towards the poles. Deeper down, differences in temperature and saltiness drive a slower worldwide circulation, sometimes called the global conveyor belt. Cold, salty water sinks near the poles and spreads through the deep ocean, and a single parcel of water may take around a thousand years to complete the circuit.

Upwelling happens where winds push surface water away from a coast or apart in the open sea, and colder water rises from below to replace it. That deep water is rich in nutrients, so upwelling zones off Peru, California, north-west and south-west Africa support enormous blooms of plankton and some of the world's most productive fisheries.

From plankton to whales

The ocean's food web rests on plankton, drifting organisms that range from microscopic algae to jellyfish. Phytoplankton, the plant-like plankton, make food from sunlight and are thought to produce roughly half of the oxygen made on Earth. Zooplankton graze on them, and every night vast numbers of small animals rise from the twilight zone to feed near the surface before sinking again at dawn, often described as the largest migration on the planet. A steady fall of dead plankton, faecal pellets and mucus, known as marine snow, drifts down into the depths, feeding deep-sea life and carrying carbon downwards.

At the other end of the scale are the ocean giants. The blue whale, up to about 30 m long, is the largest animal known to have existed, yet it feeds mainly on tiny krill. The whale shark, the largest fish, is also a gentle filter feeder. Sperm whales dive deeper than 1,000 m to hunt squid, and a Cuvier's beaked whale has been recorded diving to nearly 3,000 m. A sunken whale carcass can feed deep-sea scavengers for years.

The deepest places and an ocean under pressure

The deepest known point is the Challenger Deep in the Mariana Trench in the western Pacific, roughly 10,900–11,000 m down; different surveys give slightly different figures. Mount Everest could sit inside it with about 2 km of water to spare. It was first reached in 1960 by Jacques Piccard and Don Walsh in the bathyscaphe Trieste. Our knowledge of the seafloor as a whole is also limited: the entire ocean has been mapped roughly from space, but the international Seabed 2030 project reported only about a quarter mapped in detail by ship-based sonar in the early 2020s.

The ocean faces several threats at once. It has absorbed more than 90% of the extra heat trapped by greenhouse gases, driving marine heatwaves and coral bleaching. It has also taken up roughly a quarter to a third of the carbon dioxide released by human activity, making seawater more acidic and harder for corals, shellfish and some plankton to build their shells and skeletons. Overfishing has depleted many stocks, with UN figures suggesting more than a third are fished unsustainably, and millions of tonnes of plastic enter the sea each year. Protected areas, better fisheries management and cutting emissions all help.

Surprising facts about Ocean & underwater

More than half of the oxygen produced on Earth is thought to come from the ocean, mostly from microscopic phytoplankton.
Mount Everest would fit inside the Challenger Deep with roughly 2 km of water still above its summit.
Earth's longest mountain range, the mid-ocean ridge, runs for about 65,000 km and is almost entirely underwater.
Measured from its base on the seafloor, Hawaii's Mauna Kea is taller than Mount Everest.
Red light disappears so quickly underwater that many deep-sea animals are red, which makes them effectively invisible.
Every night, vast numbers of small sea creatures swim hundreds of metres up to the surface to feed, then sink back down at dawn.

Frequently asked questions

How deep is the ocean?: The average depth is about 3.7 km. The deepest known point, the Challenger Deep in the Mariana Trench, is roughly 10,900–11,000 m deep, with figures varying slightly between surveys.
Why is the ocean blue?: Water absorbs red, orange and yellow light more strongly than blue, so blue light travels furthest and is scattered back to our eyes. Plankton, sediment and reflections of the sky can shift the colour towards green, grey or brown.
What is a seamount?: An underwater mountain, usually an extinct volcano, that rises from the seafloor without reaching the surface. Currents flowing around seamounts can bring up nutrients, making them hotspots for fish, sharks, turtles and whales.
How much of the ocean floor has been mapped?: The whole seafloor has been mapped at low resolution using satellites, but the Seabed 2030 project reported that only about a quarter had been mapped in detail by sonar in the early 2020s. The figure is rising each year.
Can I dive in the ocean in 3D in the app?: Yes. You start floating on the surface of the open Pacific and can dive down onto a seamount topped with a coral reef, swimming among fish schools, turtles, rays and whales in interactive 3D.

Keep exploring

The landscapes in Ember’s Universe are procedural 3D scenes modelled on real places. The landforms, plants and light follow the real thing, but the details are generated, not mapped.

Sources