All of Earth's water in a single sphere (2019)

Visualization, Scale, and Intuition

• Many find the spheres visually striking but hard to intuit; the 860‑mile water sphere looks “small” next to Earth despite reaching far into space.
• Several note that oceans are just a very thin film on a large rock: average ocean depth (~few km) vs Earth’s ~12,700 km diameter.
• Some argue the graphic is inherently misleading because it compares volume to planetary volume; others say it effectively conveys the thinness and preciousness of Earth’s water.
• Suggestions include overlaying “equivalent depth” over the U.S., using cubes instead of spheres, or comparing to “accessible crust” volume rather than the whole planet.

Freshwater vs Total Water

• The smallest sphere (lakes and rivers) and the medium sphere (all liquid freshwater including groundwater and swamps) are highlighted as surprisingly small.
• Back‑of‑envelope calculations show large per‑person allocations if all freshwater were evenly divided, but commenters stress distribution, accessibility, and pollution matter more.

Water in the Mantle and Definitions of “Water”

• Multiple comments note newer research suggesting the mantle may contain as much H₂O (bound in minerals) as all oceans combined.
• The USGS numbers are based on a 1993 source and exclude this mantle water.
• Debate over whether mantle H₂O should “count” as water: some say it’s hydroxyl in minerals, effectively inaccessible; others still see it as part of Earth’s total water inventory.

Physics, Shapes, and Math Pedantry

• Discussion on whether a Ceres‑sized water sphere would stay intact in space: gravity would form a sphere, but stability depends on temperature (freezing vs boiling/sublimation).
• Repeated riffs on how humans misjudge curved volumes; spheres and small radius changes drastically affect volume.
• Lengthy side thread on “polynomial vs exponential” growth and the colloquial misuse of “exponential.”

Comparisons and Thought Experiments

• Comparisons to Ceres, icy moons (Europa, Ganymede), and Jupiter’s liquid hydrogen “ocean.”
• Speculation about crashing Ceres or Europa into Mars to terraform it, with pushback on catastrophic side effects and timescales.
• Related analogies: all mined gold as a ~22 m cube, all humans as a ~1 km “meat sphere,” atmosphere as a sphere comparable in size to the freshwater one.