For example, in the Earth's crust there is a limit to the total weight that each point on the Earth's surface should support. In mathematical terms, this concept of balance is defined by the “compensation depth” which is approximately 70 miles below the Earth's surface. In short, for the Earth's crust to maintain the same mass and pressure, there must be the same amount of mass everywhere. Isostacy controls the local and regional elevation levels of continents and the ocean floor in congruence with the total weight that the underlying rocks can support. This phenomenon and the behavior exhibited by the plates are often compared to an iceberg floating in the sea in which the greatest mass is immersed. Additionally, gravity plays an important role in understanding the amount of pressure the surface must experience for such movements to occur. For example, when gravity pulls the Earth down, the plates begin to move causing isostacy to create balance across the planet. For years, scientists have tried to explain why this phenomenon occurs in relation to the thickness of the earth, gravity and the density of the soil. Only scientists John Fillmore Hayford and John William Bowie had a concrete understanding of isostacy and its processes. Hayford and Bowie “were able to demonstrate that gravity anomalies are directly related to topographic features. This essentially validated the idea of ​​isostasy, and Hayford and Bowie further established the concept of the depth of isostatic compensation. Both gentlemen published books on isostasy and geodesy. Hayford was the first to estimate the depth of isostatic compensation and to establish that the Earth has an oblate spherical shape (an arcuate or ellipsoidal sphere) rather than a true sphere. (edited by Encyclopedia Britannica,