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Explore the Ocean

What we know, how we know it, and what we have never seen.

A short tour, written the way the exhibits would be: every figure links to its source, and we keep the qualifiers that make it true. The Research page lists each source's date (or says it is undated).

The big picture

One ocean, mostly deep, mostly unseen.

71%

The ocean covers about 71 percent of Earth's surface and holds about 97 percent of its water.Source: NOAA, The Ocean (undated)

Source undated · checked 18 October 2026

3,682 m

The average depth of the ocean is about 3,682 meters (12,080 feet), an estimate calculated in 2010 by NOAA and Woods Hole scientists using satellite measurements.Source: NOAA, How deep is the ocean? (undated)Source: NOAA OE, How deep is the ocean? (undated)

Source undated · checked 18 October 2026

≈ 11,000 m

The deepest known point, Challenger Deep in the Mariana Trench, is nearly 11,000 meters down; NOAA gives about 10,935 meters (35,876 feet).Source: NOAA, How deep is the ocean? (undated)

Source undated · checked 18 October 2026

28.7%

As of April 2026, 28.7 percent of the global seafloor had been mapped in high resolution with modern sonar.Source: Seabed 2030, Global seabed mapping reaches new milestone as five million square kilometres added in a year (20 April 2026)Source: NOAA, How much of the ocean has been explored? (April 2026)

As of 20 April 2026

< 0.001%

People have directly seen, with cameras, robots or crewed submersibles, less than 0.001 percent of the deep seafloor, an area roughly the size of Rhode Island.Source: NOAA, How much of the ocean has been explored? (April 2026)Source: Bell et al. 2025, How little we've seen: A visual coverage estimate of the deep seafloor (7 May 2025)

As of 2025–2026

≈ 250,000

About 250,000 marine species have been formally named and accepted; estimates of how many exist in total vary widely.Source: WoRMS, 250,000 accepted marine species (13 May 2026)

As of 13 May 2026

Interactive preview

Light fades. Pressure climbs.

The ocean is divided into zones by depth and light. Pick any depth to see where you are.

Ocean depth zones from the surface to 11,000 meters, with a marker at 200 meters0 m200 m1,000 m4,000 m6,000 mAverageChallenger Deep

200 m(656 ft)

Zone
Twilight zone
Faint blue light, too dim for photosynthesis.
Pressure (approximate)
About 21 atmospheres
Roughly one more atmosphere for every 10 meters of seawater, on top of the one atmosphere of air at the surface.
  • Average ocean depth: about 3,682 m
  • Challenger Deep, the deepest known point: ≈ 11,000 m

Zone boundaries follow NOAA and are conventions, not sharp lines.Source: NOAA 1, Layers of the Ocean (undated)Source: NOAA 2, How deep is the ocean? (undated)Source: NOAA 3, How does pressure change with ocean depth? (undated)

Measured, predicted, filled in, seen

How do we know how deep it is?

A seafloor map looks complete, but it is usually stitched together from very different kinds of information. Try each one.

Illustrative schematic · Not real data

Illustrative seafloor cross-sectionA schematic, not real data: a slice of ocean from the surface to a seafloor with a small ridge and a tall seamount, comparing how much of it each method reveals. A satellite above sees only a smooth, approximate profile; two ships send fans of sonar down and measure detail beneath their tracks, labelled ship track; a dotted estimate fills the gap between the tracks; two small robots light up tiny patches of the floor.

Satellites measure tiny bumps in the sea surface caused by the pull of large seafloor features, and depth is predicted from them. It covers the whole ocean, but coarsely: smaller features vanish and big ones can be the wrong height.Source: NOAA, Seafloor Mapping (explainer) (undated)Source: NOAA OE, Seamount in the Jarvis Unit, PRIMNM (EX1705 background image) (2017)

Seamounts rendered in color from sonar data, rising above a dark wireframe grid showing the shape those same seamounts were predicted to have from satellite data
Predicted seafloor versus measured seafloor. Seamounts near Wake Island, mapped by NOAA Ship Okeanos Explorer in 2016. The wireframe is the satellite prediction; the color is what sonar measured. Credit: NOAA Ocean Exploration.

Satellite-derived maps cover the whole seafloor, but only coarsely: NOAA gives their resolution as about 1.5 kilometers (about a mile), so smaller features such as volcanic craters and shipwrecks can be missed.Source: NOAA, Seafloor Mapping (explainer) (undated)

On a 2017 NOAA survey in the Pacific Remote Islands Marine National Monument, sonar found a seamount whose height differed by about 1,700 meters from what satellite data had predicted.Source: NOAA OE, Seamount in the Jarvis Unit, PRIMNM (EX1705 background image) (2017)

Global grids such as GEBCO record, cell by cell, what each depth is based on: for example, a direct measurement, a prediction from satellite gravity, or computer interpolation.Source: GEBCO, GEBCO Type Identifier (TID) Grid (undated)

Ocean and climate

The ocean is doing a lot of work.

91%

Ocean warming accounted for 91 percent of the heating in the climate system between 1971 and 2018.Source: IPCC, AR6 Working Group I, Summary for Policymakers (2021)

As of 2021

≈ 29%

Over 2015–2024 the ocean absorbed about 29 percent of the carbon dioxide released by human activities.Source: GCB 2025, The Global Carbon Budget FAQs 2025 (November 2025)

As of November 2025

−0.1 pH

Average surface-ocean pH has dropped by about 0.1 units since the Industrial Revolution, about a 30 percent increase in acidity. Seawater is still basic, not acidic.Source: NOAA, A primer on pH (undated)

Source undated · checked 18 October 2026

≥ 50%

The ocean produces at least half of Earth's oxygen, and marine life uses roughly the same amount.Source: NOAA, How much oxygen comes from the ocean? (undated)

Source undated · checked 18 October 2026

Life without sunlight

Discoveries that changed biology.

In 1977 scientists diving in the submersible Alvin on the Galápagos Rift, in the eastern Pacific, found springs of warm water on the seafloor surrounded by communities of animals living without sunlight.Source: WHOI, The Discovery of Hydrothermal Vents: 1977 (undated)

These NOAA photographs show deep-sea coral, methane hydrate and mineral nodules. Each caption follows NOAA's own identification; nothing is invented.

A tall pale hydrothermal chimney rising from the seafloor into dark blue water, with black smoke pouring from its upper part
Black smoker chimney. A vent field on the Mariana back-arc spreading center, western Pacific. Credit: NOAA Ocean Exploration.
A pale fan-shaped deep-sea coral colony on dark rock, its branches densely lined with small pink brittle stars
Coral colony with brittle stars. Callogorgia delta colonized by brittle stars (Ophiuroidea). Credit: NOAA Ocean Exploration.
A meter-wide mass of white ice-like methane hydrate beneath a carbonate ledge, surrounded by tubeworms, clams and anemones
Methane hydrate under a carbonate ledge. Seascape Alaska 3 expedition, Dive 04. Credit: NOAA Ocean Exploration.
A seafloor plain densely covered in dark potato-sized polymetallic nodules
Polymetallic nodules. 2026 American Samoa expedition, Dive 04, about 5,140 m. Credit: NOAA Ocean Exploration.

River to ocean

From Bethlehem to the Atlantic.

The watershed outside the door would be the starting point. Follow the water.

  1. PoconosLehigh River headwaters
  2. BethlehemMonocacy Creek meets the Lehigh
  3. EastonThe Lehigh joins the Delaware
  4. TrentonHead of tide: the estuary begins
  5. PhiladelphiaTidal river and port
  6. Delaware BayFresh and salt water mix
  7. Atlantic OceanBetween Cape May and Cape Henlopen
103 mi
The Lehigh River runs about 103 miles from the Poconos to Easton, where it joins the Delaware River.Source: PA DCNR, Lehigh Gorge State Park (Lehigh River, 103 miles to Easton) (undated)
Source undated · checked 18 October 2026
1,359 sq mi
At the USGS gauge at Glendon, just above its mouth, the Lehigh drains about 1,359 square miles.Source: USGS, Water-data report, station 01454700, Lehigh River at Glendon, PA (Water Year 1999)
As of Water Year 1999
13,539 sq mi
The Delaware River Basin covers 13,539 square miles across Pennsylvania, New Jersey, New York and Delaware.Source: DRBC, 2008 Annual Report (basin area by state) (2008)
As of 2008
14.2 million
About 14.2 million people rely on water from the Delaware River Basin.Source: DRBC, Delaware River Basin population update (8 February 2023)
As of 2020 data (published 2023)

Diagram, not a map; stops are in order but not to scale. Estuary extent (Trenton to the bay mouth):Source: PDE, About Us (undated)

Ocean worlds

Oceans beyond Earth?

Several moons may hide oceans under ice. The careful word is “may”: these oceans are inferred, not seen, and no life has been found.

Earth seen from space, centered on the Pacific Ocean, which fills almost the entire visible hemisphere
Earth, Pacific hemisphere. NASA Blue Marble (2002), orthographic projection at 160°W. Credit: NASA.