1. The problem statement, all variables and given/known data "Estimate the mass of water in all the World’s oceans." 2. Relevant equations I know the following: Two-thirds of the earth is sea. The density of seawater is 1025 kg/m3. Radius of the earth = 6.3*106m. 3. The attempt at a solution Let's assume that the earth's crust is a spherical shell that has a thickness of 0.001 times the radius of the earth. So, the volume of the crust = (4[tex]\pi[/tex]r2)(router-rinner) = 3.1*1018 m3. So, volume of seawater = 2.1*1018 m3. So, mass of seawater = 2.1*1021 kg. Is the answer reasonable? How might I improve it?