Water always finds its level, so oceans can’t curve.
Quick reality-check: “Level” means perpendicular to gravity, not “perfectly flat.” Over Earth’s 12,742-km diameter the surface curves only about 8 inches per mile²—too small to notice locally, but obvious from aircraft, satellites and the 400 km-high ISS, whose crews have taken millions of photos of the curved blue limb.
Why is this claim made?
The claim arises from a misunderstanding of the word “level.” In geodesy, "level" refers to a surface perpendicular to gravity at every point, not a perfectly flat plane. Flat-Earth proponents assume level means flat, leading to the mistaken belief that oceans cannot curve.
Why the claim doesn’t work
Earth’s immense size means its curvature is imperceptible over short distances. Surveyors and engineers account for this curvature in large-scale projects. Satellite and ISS imagery, as well as long-range laser and builder’s line experiments, show the drop over distance.
Evidence against the claim
- Photos from the ISS and high-altitude aircraft clearly show the curved limb of Earth.
- Laser and builder’s line experiments across lakes show the surface drops away by about 8 inches per mile².
- Surveying and geodetic measurements routinely account for Earth’s curvature.
Try it yourself: Stretch a taut builder’s line across a long lake at dusk; shine a laser just skimming the water at one end. A calibrated surveying pole at the other end will show the beam sitting above the surface, revealing the gentle drop.
Summary
The claim confuses “level” with “flat.” Earth’s curvature is subtle but measurable and visible with the right tools and vantage points. Modern geodesy, satellite imagery, and simple experiments all confirm that oceans do curve to conform to Earth’s spherical shape.
Links to additional resources