By Lesley Barker • Updated Mar 24, 2022
When a satellite or rocket captures an image of the planet, it shows the Earth’s surface—or crust—where we live, travel, and interact with land and water. This layer contains the highest peaks and the deepest ocean basins.
Measuring from the North Pole to the South Pole gives a meridional length of 7,899.83 miles. A straight‑line diameter across the equator is 7,926.41 miles, while the equatorial circumference is 24,901.55 miles.
The crust is divided into continental and oceanic sections. Continental crust, largely granite, averages 25 miles thick. Oceanic crust, composed mainly of basalt, averages 5 miles. The surface rocks belong to the three major categories: igneous, sedimentary, and metamorphic.
Mount Everest tops the Earth’s surface at 29,028 feet above sea level. The Mariana Trench dips 36,198 feet below sea level, representing the planet’s deepest point.
Below the crust lie the mantle, outer core, and inner core. The mantle is 1,400 miles thick; the outer core, a molten mix of iron, nickel, and other metals, extends another 1,400 miles. The solid inner core, 800 miles thick, consists mainly of iron and nickel with about 10% sulfur.
The boundary between crust and mantle, known as the Mohorovičić Discontinuity (Moho), is crucial in understanding tectonic and volcanic activity. Geologists employ satellite imagery, sonar, and seismic data to map and monitor the surface and its dynamic changes.
