Earth, scaled to the size of a billiard ball, would present a surface that meets or exceeds standard manufacturing smoothness. Planetary radius dwarfs the vertical range between the deepest ocean trenches and the highest mountain peaks. Relief becomes a minor deviation from a nearly perfect sphere.
At real scale, the Mariana Trench reaches several thousand meters below sea level, while Mount Everest rises several thousand meters above it. In geophysical terms, both are small perturbations relative to Earth’s mean radius. The ratio of maximum elevation change to planetary radius is far below the threshold that a human fingertip could detect on a billiard ball.
This extreme smoothness reflects isostasy and long-term erosion, which redistribute rock and sediment through plate tectonics and hydrological cycles. Crustal deformation, subduction, and seafloor spreading constantly work to limit vertical extremes. The result is a planet that hosts the deepest known oceans and tallest continental peaks, yet still qualifies as an almost ideal sphere when judged by precision engineering standards.
