Continentality and the gravitational field of the Earth

Satellite observations provide some information about zonal harmonics J2, J3, … J6 of the gravitational field. For a hydrostatic earth (all surfaces of equal density are level), odd harmonics vanish and even harmonics can be computed from precession and geophysical data. We have compared the nonhydrostatic (observed minus hydrostatic) harmonics with those calculated for the known distribution of continents and some reasonable assumptions about density in the crust. The two sets of values do not agree, and this raises the possibility that density variations in the mantle, perhaps unrelated to the distribution of continents, are the important factor in determining the gravitational coefficients of low order.