Empirical Earth · Shape, Curvature & the Horizon

The abyssal plains are the smoothest on Earth — and still curved

The claim

“The abyssal plains are the flattest places on Earth, so the sea floor is flat.”

What is measured

Abyssal plains have slopes below 1:1000 (under about 1 m per km). They are extraordinarily smooth, and they follow the curved geoid. Smooth is not the same as flat-plane.

What would show this is wrong

an abyssal plain shown to be a true flat plane (zero curvature) over its full thousands-of-km width, rather than just low-slope at every local patch.

Sources

  1. Refraction, Snell's law & refractive index of air/water. Standard optics; refractive index of air via the Ciddor/Edlén equations. E. Hecht, Optics ; NIST refractive-index references. Snell's link
  2. The geoid and “level” as an equipotential surface. Still water settles onto a surface of constant gravitational potential — the curved geoid. NOAA / NGS. NOAA: geodesy / geoid link
  3. Abyssal plains — the smoothest, lowest-relief large surfaces on Earth (slope < 1:1000). Sediment-blanketed deep-ocean floor at 3,000–6,000 m; smooth locally, conforming to the curved geoid. link
  4. The geoid undulates by ~±100 m. Mean sea level follows the geoid, an equipotential of Earth’s gravity that departs from a smooth reference ellipsoid by up to about ±100 m because mass is une link
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