The descent · 0 m

ABYSS

Below you is eleven kilometres of water. Scroll, and it will take the light apart one colour at a time — and this page has no light of its own. What you see from here down is only what the water lets through.

Nothing here is a mood. The colours on this screen are computed from measured attenuation coefficients for the clearest ocean water, the pressure from the standard oceanographic depth relation, the animals from published depth ranges. Where the sources disagree, this page says so.

Epipelagic · Sunlight zone

Red is the first to go

Water is not clear. It is a filter that happens to be very good at one end of the spectrum and very bad at the other. Pure water absorbs red light at 0.624 per metre and blue light at 0.011 per metre — a difference of about fifty-nine times.

That single ratio is why the sea is blue, why blood looks black on a reef, and why the gauge on the left is already emptying its top bar. At ten metres, less than one part in five hundred of the surface's red light is left.

You are ten metres down. Red still exists — there is simply none of it here to reflect.

Absorption coefficients: Pope & Fry (1997), measured for pure water. The bars use diffuse attenuation for Jerlov Type I — the clearest open ocean — which is higher than pure-water absorption because it includes scattering.

Epipelagic · 60 m

Then orange, then yellow, then green

They leave in order of wavelength, and the order never varies. Orange goes at a few tens of metres, yellow soon after, green holds on into the hundreds. Only the blue-green window around 470–490 nanometres travels far, and everything that lives down here has been shaped by that window.

Watch the swatches, not the bars. Each one is that wavelength as it would actually appear at this depth. By the time they are all the same colour, there is nothing left to see by.

Epipelagic · 200 m

The last depth where a leaf would pay its way

Two hundred metres is where about 1% of the surface light remains. That figure is the definition of the euphotic zone, and it is drawn there for a reason: below one per cent, photosynthesis costs a plant more energy than it returns.

Every forest, every crop, every alga in the ocean lives above this line. Below it, the entire remaining volume of the sea — and it is the overwhelming majority of the habitable space on this planet — runs on what falls from here, or on chemistry with no sun in it at all.

Look at the rail on the left edge. The band you have just crossed is drawn to true scale against the whole water column. It is that thin.

Mesopelagic · Twilight zone

Where most animals make their own light

MBARI spent seventeen years pointing cameras into the water column off Monterey and counting what came past — over 350,000 animals across 240 dives. Of everything they saw, 76% could produce light.

The stranger result is that the fraction barely moved with depth. Between 48% and 77% at every level they sampled, even as the total number of animals collapsed. Bioluminescence is not a deep-sea specialisation. In the open ocean it is simply the normal condition.

Mesopelagic · 700 m

A light that makes you invisible

There is still a faint blue glow from above here, and against it every body is a silhouette. So the hatchetfish carries rows of lights along its belly and runs them at the brightness of the water overhead. Seen from below, its shadow simply is not there.

It is a closed loop: photophores angled back toward the eye let the fish measure its own output against the ambient and correct in real time. The bobtail squid solves the same problem with a farmed colony of Aliivibrio fischeri, held at about a third of the intensity of the moonlight above it.

Bathypelagic · Midnight zone

From here down, every photon was made by something alive

One thousand metres. No instrument aboard a submersible can detect sunlight at this depth. The bars on the gauge are empty, and they will stay empty for the remaining ten kilometres.

This page changes its rule here, and it is worth being plain about it. Held strictly to the physics, the screen would now be black and you would read nothing. So the palette switches to the only light that still exists down here — the blue-green of living things, around 480 nanometres. That is not a cheat. It is the actual lighting condition at this depth.

Everything you can see for the rest of this descent is being lit by an animal.

Bathypelagic · 2,000 m

The jellyfish that screams for help

Grabbed by a predator, Atolla wyvillei does not flee into the dark. It lights a ring of blue that chases around the rim of its bell — a signal visible for tens of metres in every direction, advertising the position of whatever is currently eating it. The point is to attract something bigger.

In 2012 Edith Widder built a plastic imitation of that ring, called it the e-jelly, and lowered it into the dark with a low-light camera beside it. It brought in the first footage ever taken of a living giant squid.

Bathypelagic · 2,500 m

Life that never needed the sun

In February 1977 the submersible Alvin made its 713th dive, onto a spreading ridge north of the Galápagos, and found warm water shimmering out of the basalt with a crowd of animals around it. Nobody had predicted a dense community with no photosynthesis anywhere beneath it.

Riftia pachyptila grows to three metres there and has no mouth, no gut and no anus. Inside it is an organ packed with about a billion bacteria per gram, running this reaction:

CO₂ + 4 H₂S + O₂ CH₂O + 4 S + 3 H₂O

Hydrogen sulphide is lethal to nearly everything, and the worm's blood carries it safely by binding it with zinc. In return the bacteria feed the worm. It puts on a metre and a half in two years — the fastest growth known for any seafloor invertebrate.

Bathypelagic · 3,800 m

Something familiar, at a depth that is not

The bow of the Titanic sits at roughly this depth, on a plain of pale sediment, being slowly eaten by iron-oxidising bacteria. The pressure here is around 380 times what you are standing in.

The mean depth of the whole world ocean is 3,682 metres. You passed it a moment ago. Everything above this line — every reef, every fishery, every shipping lane, every place a human being has ever swum — is the shallow part.

Abyssopelagic · The abyss

A whale falls, and a town appears

In 1987 Craig Smith's team put Alvin down in the Santa Catalina Basin, at 1,240 metres, and landed by accident on a whale skeleton. What they found on it was a community nobody knew existed — and the same thing happens all the way down to the depth you are at now.

Scavengers strip the soft tissue at up to 60 kilograms a day. Then bone-eating worms and crustaceans move in. Then, for something like fifty to a hundred years, sulphate-reducing bacteria work through the fats locked inside the bones and produce hydrogen sulphide — and the same chemosynthetic animals that live at vents colonise the carcass.

The carbon arrives about two thousand times faster than it would as marine snow. One thirty-tonne whale delivers what a hundred square metres of seafloor would otherwise receive in a millennium.

Hadopelagic · The hadal zone

Named after the underworld, in 1956

Below six kilometres the seafloor is no longer a plain but a set of trenches, and they are not connected to one another. Each is an island of extreme pressure with its own fauna. Anton Bruun named the zone after Hades.

There is a theoretical floor for fish. Cells at depth need osmolytes to keep their proteins from being crushed out of shape, and the concentration of the one fish use — TMAO — cannot rise past the point where it makes the blood saltier than seawater. Run the numbers and you get a limit near 8,200 metres.

In August 2022 a camera filmed a snailfish at 8,336 metres.

It has not been assigned to a species. A related fish was caught days later at 8,022 metres in the Japan Trench, and that one has a name — but the deeper individual, the record holder, is still just Pseudoliparis sp.

Hadopelagic · 8,848 m

Everest, upside down, does not reach

Take the mountain from sea level to summit and stand it on the floor of the Challenger Deep. The peak — the place where the air is too thin to keep you conscious, where people leave bodies because they cannot be carried down — finishes 2,087 metres below the surface.

You would still have to swim the height of six Burj Khalifas to get out.

Challenger Deep · 10,935 m

The bottom, and what is on it

The deepest point measured on Earth is 10,935 metres, give or take six, established by pressure transects during crewed dives in 2019 and 2020. Earlier figures ran from 8,184 metres in 1875 to a 1957 reading of 11,034 metres that turned out to be an outlier. Depth is not a fact you look up; it is a measurement with a method attached.

At 10,898 metres, in a Japanese database of deep-sea debris compiled from five thousand dives, there is a photograph of a plastic bag.

Of amphipods collected from six trenches, 72% had plastic inside them. In the Mariana Trench it was every single one.

The same animals carry PCBs and flame retardants at concentrations up to fifty times those found in crabs from the most polluted rivers in China. There is no industry down here. It arrived by falling.

Looking back up

Almost none of this has been looked at

As of April 2026, 28.7% of the seafloor has been mapped at modern resolution — about 104 million square kilometres, and five million of them added in the last year alone.

Mapped is not seen. Counting every crewed and robotic dive since 1958, the area of deep seafloor that a human being has actually laid eyes on is under one thousandth of one per cent. Roughly the size of Rhode Island. Five countries account for 97% of it.

In 1979 a company dragged a test collector across the Pacific abyssal plain. In 2023 someone went back. The tracks were still there — one to three metres wide, up to eighty centimetres deep, forty-four years on. At that depth the sediment settles at a millimetre or so per century.

Commercial mining has not started. In March 2026 the International Seabed Authority again failed to agree a mining code, forty states now back a moratorium, and a parallel licensing route has opened outside the treaty.

Colophon

How this was computed

One number drives this page. Scroll position becomes a depth; everything else is a function of it. No framework, no external requests, no analytics.

Light

Beer–Lambert, I(d) = I₀ · e^−Kd·d, evaluated at six wavelengths with diffuse attenuation coefficients for Jerlov Type I water. Each band's swatch is that wavelength rendered at its remaining intensity; the page's own accent colour is the sum of all six.

Pressure

Saunders (1981), inverted. Seawater compresses as it deepens, so the familiar ρgh with surface density underestimates the bottom by about 2.5%. You will often see 1,086 atmospheres quoted for the Challenger Deep; accounting for compression gives closer to 1,115.

Temperature

A representative western Pacific profile, pinned at the ends to in-situ measurements in the trench. The rise below six kilometres is real — adiabatic compression warms the water by about a degree on the way to the bottom, even though its potential temperature keeps falling.

The scale is not linear

If it were, the two hundred metres where all of the optics happen would be 1.8% of this page. The scroll is stretched near the surface and compressed below. The rail on the left edge is drawn to true scale so you can see exactly how much stretching is going on.

What is not known

Several numbers on this page are disputed by their own sources, and those are flagged where they appear. Seven of the animals in the codex have no established common name in Korean, Japanese or Chinese; rather than invent one, those entries show the scientific name. Vanishing depths per colour vary by an order of magnitude with water clarity.

• OpticsPope & Fry, Applied Optics 36 (1997). Jerlov, Marine Optics (1976).
• PressureSaunders, J. Phys. Oceanogr. 11 (1981).
• DepthChallenger Deep 10,935 ± 6 m — Deep-Sea Research I (2021), from crewed pressure transects.
• BioluminescenceMartini & Haddock, Scientific Reports 7:45750 (2017).
• Deepest fish8,336 m, Izu-Ogasawara Trench, 2022. Theoretical limit: Yancey et al., PNAS (2014).
• PlasticChiba et al., Marine Policy (2018). Jamieson et al., Royal Society Open Science (2019).
• MappingSeabed 2030 (April 2026). Bell et al., Science Advances (2025).
• MiningNature (2025), on the 1979 test tracks revisited in 2023.
• AnimalsFishBase, WoRMS, MBARI and the primary descriptions linked from each codex entry.

Built without a framework. Every byte — fonts, code, illustration — is in the file you are reading. Nothing is fetched.