the Mariana Trench in Western Pacific Ocean dropping to 11,035 meters below mean sea level ( Oceanclopedia: Mariana Trench ). Additionally, the Earth is slightly oblate ( Cox-240 ) due to the centrifugal force (see below). Equatorial radius: 6378.136 km Polar radius: 6356.753 km 6378.136-6356.753 = approx 21 km The Earth