How Deep is Challenger Deep?

Deep below the coasts of the Pacific ocean, the tectonic plates of Earth's crust grow, spread, compress, drift, and otherwise grind against their neighbors.

The Pacific Plate is the largest of these fractious rock shells, floating atop a roiling sphere of magma.

Along its eastern edge, the Pacific Plate is slowly spreading away from, or sliding along, its neighbors. Much of the western edge, some of the oldest material of Earth's crust, and is therefore comparatively dense and cool, is colliding with its neighbors under interminable force, subducting below neighboring plates.

This plunging of the Pacific Plate beneath the younger and lighter Mariana Plate has formed a deep crescent-shaped wrinkle at their meeting.

The Mariana Trench is a 2,550 kilometer (1,580 miles) long groove that plunges to the greatest depths on Earth.

The Mariana Trench runs parallel to an archipelago, the Mariana Islands. The islands, the highest portion of the younger and lighter plate, were formed as a geologic counterpoint to the collision of plates, arcing upward through friction and volcanic uprise.

At the southern end of the Mariana Trench lies a relatively small slot of exquisite depth: Challenger Deep.

Challenger Deep plunges to 10,924 meters (35,840 feet; 6.788 miles).

In 1873 the HMS Challenger embarked on an eastward circumnavigation of Earth. Aboard were John Young Buchanan and John Murray, pioneers in the relatively new field of oceanography.

Two years into the scientific expedition, Challenger attempted to make landfall at the island of Guam, but was blown west of their destination. The team took the opportunity to make "soundings" (lowering a weighted rope to determine the depth of the sea-floor) along this unplanned track and chanced upon the erratic depth of the Mariana Trench, only fifteen miles from what is now known as Challenger Deep.

In 1960, the Trieste, a small free-diving submersible craft with a buoyancy tank and small spherical pressurized vessel crewed by Jacques Piccard (who designed the craft) and Don Walsh made the first crewed descent to Challenger Deep.

The descent took nearly five hours though only twenty minutes were spent at the bottom due to concern over a crack that developed in the window.

Imagine sitting in a boat directly over Challenger Deep, and a hole opens up. An impossible shaft all the way down to the bottom. Now imagine you are a skydiver, but instead of jumping from a plane, you jump from the boat and begin your free-fall plummet to the bottom.

Your speed would rapidly increase until you were about 450 meters (1,476 feet) down at which time you would hit terminal velocity and hold steady at a screaming 195 kilometers per hour (122 miles per hour).

You would continue to rocket toward the bottom of Challenger Deep for the longest three and-a-half minutes of your life. This is enough time to listen to the entirety of the Beatles' Across the Universe, and still have four seconds remaining to pull your chute and land safely.

But of course there is no shaft of open air exposing Challenger Deep to the surface. Instead, consider swimming.

Not just any sort of swimming, though. Consider the extremely dangerous world of competitive no-limits free-diving.

Divers hold their breath and plunge to enormous depths and resurface, vying for the title of deepest. The current world record for a no-limits free-dive is held by Herbert Nitsch at a lung-macerating 253 meters...

...which, in the context of Challenger Deep there at the bottom, looks like that little blip at the top.

Upon ascent from this record depth, Nitsch experienced several strokes due to decompression and required an immediate medical evacuation and extensive rehabilitation.

This perilous record-setting depth to the edge of humanity's capacity to survive would have to be spanned another 49 times to reach the bottom.

The weight of an ocean at Challenger Deep squeezes from all directions exerting a pressure more than 1,071 times of that felt at sea-level.

A one-liter bottle of air carried to Challenger Deep would be crushed to the volume of a pea.

A deep breath would be compressed to the volume of five peas. Nearly nothing.

Speaking of breath and pressure, one of the greatest travails of summiting Mt. Everest, the world's highest peak, is that the atmosphere, and oxygen levels, at that elevation are dangerously low. It may take weeks of acclimation for a climber to adapt to the rarefied air.

But even if Everest were placed at Challenger Deep, it would still lie under more than two kilometers (1.2 miles) of water and be shrouded in absolute darkness.

In fact, sunlight capable of supporting photosynthesis only penetrates to the line marked above.

This topmost 200 meters, or euphotic zone, is home to microscopic phytoplankton responsible for producing half of Earth's oxygen. Every other breath we take comes from the light-bathed microscopic organisms here.

Beyond 1,000 meters, however, absolutely no sunlight penetrates. Save for the rare bio-luminescent pulse of sea life, a descent through the vast majority of water above Challenger Deep is one of utter darkness.

Its scale can be dizzying when beheld from the rim. The Grand Canyon, at 1,857 meters (6,093 feet; over one mile), is so deep that it has a different climate at the bottom.

Were we to scoop out the Grand Canyon and use it as an impossibly convenient unit of reference...

...it would sink this deeply below the surface of the sea.

Were it Grand Canyons all the way down, we'd need six of them.

Here is the Burj Khalifa, the world's tallest building at 830 meters (2,772 feet) nestled charmingly within the Grand Canyon.

It would take over 13 Burj Khalifas to reach the ground floor of Challenger Deep.

The ground floor of the sea is a precipice-strewn hotbed of geologic activity. Mountains and canyons dwarf those found on dry land.

The rim of the Mariana Trench, the chasm where Challenger Deep is found, sits at about six kilometers under sea level.

Six kilometers is already exceedingly deep.

In fact, only the most precipitous trenches and depressions plunge to such depths. Here is what remains of Earth's oceans when drained six kilometers.

Were we to stand at the edge of this new Mariana Sea, Challenger Deep would still be 4,924 meters deep—nearly five kilometers, or three miles.