With oceans making up almost 71 per cent of the Earth’s surface, scientists have been investigating the big blue for centuries. But their work is far from done: our seas are so large and deep that they're still being explored today.
In many ways, we know more about the surface of Mars than we do about our oceans, with many underwater mysteries still unsolved. We don't even know, for instance, what some seabeds actually look like.
What’s more, there are some truly weird, wonderful, and horrifying deep sea creatures that live in the dark recesses of the sea (including the ever-popular blobfish).
Just how deep is the ocean? Read on below to find out everything there is to know about the depth of the sea, how it got so deep, and much much more.
How deep is the ocean?
At 10,935m (35,876 feet) in depth, the Challenger Deep, found at the south end of the Mariana Trench is the deepest point in Earth's oceans. The point is in the Pacific Ocean, east of the Philippines.
Challenger Deep is deeper than Mount Everest (8,849m) is tall, alongside the tallest mountain on Earth, Mauna Kea, which is itself partly submerged underwater. Challenger is also28 times deeper than the Empire State Building is tall.
The ocean's deepest point is named after the HMS Challenger, whose crew first sounded the depths of the trench in 1875.
The exact depth of the Challenge Deep was discovered in 2021 thanks to remote-operated submersible vehicles.
On average, the ocean is around 3.7km deep (3,688m to be exact), according to the USNational Oceanic and Atmospheric Administration (NOAA).
Why are oceans so deep?
Oceans are as deep as they are because of subduction. This is where two of Earth's two tectonic plates meet, with one sliding beneath the other. These two converging tectonic plates create deep trenches and troughs in the ocean.
According to Planetary Science Letters, The Challenger Deep's great depth “is a consequence of the unusual regional tectonics". Depths as extreme as those found in the Challenger Deep make up the so-called Hadal Zone. This zone of deepness consists of depths between 6,000-11,000 meters.
How deep in the ocean have humans explored?
The extreme pressure at the bottom of the deepest parts of the ocean makes it monumentally difficult to explore and study. However, with the use of manned submersibles and remotely operated vehicles, we have managed to explore incredible depths.
Humans have reached the bottom of the Challenger Deep a number of times, meaning humans have explored the deepest point of the ocean. This was first achieved in 1960 by Jacques Piccard and Don Walsh.
Astronaut Kathryn Sullivan and adventurer Vanessa O’Brien became the first women to reach the bottom of the Challenger Deep in 2020. Due to this expedition, we now know that its surface is not flat, as once thought, but gently sloping. In total, the dive took 11 hours to complete.
What creatures are in the ocean's depths?
The hadal environment (the darkest depths of the ocean, 6,000-11,000m) is home to some weird and wonderful life forms.
There are specialised fish, gastropods, and other metazoan organisms living down there that are able to cope with the obscene level of pressure, total lack of light, and extreme temperatures. Read more about deep sea creatures.
At the deepest point of the ocean floor, scientists have found the likes of sea cucumbers, scale worms, polychaete worms, shrimp, and microorganisms.
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