The total mass of sediments on the ocean floor is estimated to be 262 × 1021 g. The overall mass/age distribution is approximated by an exponential decay curve: (11.02 × 1021 g)e−0.0355t Ma. The mass/age distribution is a function of the area/age distribution of ocean crust, the supply of sediment to the deep sea, and submarine erosion and redeposition. About 140 × 1021 g of the sediment on the ocean floor is pelagic sediment, consisting of about 74% CaCO3, with the remainder opaline silica and red clay. Of the sediment on the ocean floor, 122 × 1021 g is detritus, mostly terrigenous, but a small portion (about 6 × 1021 g) is volcanic. Because very little pelagic sediment is obducted, virtually all of the pelagic sediment mass and some fraction of the terrigenous sediment is being subducted at a rate estimated to be about 1 × 1021 g per million years. The composition of sediment on the ocean floor differs significantly from that of average passive margin and continental sediment, so that the loss of ocean floor sediment through subduction may drive the composition of global sediment toward enrichment in silica, alumina, and potash and toward depletion in calcium.

We have used average continental elevations for 1‐degree‐square areas to construct detailed continental hypsographic curves. The curves available up to the present have been those prepared by Kossinna, but they suffer from some drawbacks, the most important being that the elevation interval is for the most part 1 km, which does not allow for very detailed work. Consequently, we have given data for each 0.1 km interval of elevation. The availability of the data on tapes allowed us also to make calculations of the average elevation of each continent, an important normalizing parameter when comparing continental hypsographic curves, and to add on the effects of the continental shelves. It has also allowed us to recalculate the amount of continent antipodal to continent and to produce a map of the world showing these areas. We have also used the detailed curves and the amounts of continental flooding during the Neozoic to derive records of sea level variation necessary to explain the amount of flooding for each continent through time.

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Sea level changes during the Neozoic have been estimated by two different methods. The first involves measuring the amount of present-day land area which was flooded during the past, and using the present-day hypsographic curve to estimate the amount of sea level rise necessary to produce this flooding. The second involves the estimation of the changing volume of mid-oceanic ridges through time, and estimating sea level changes after having allowed for isostatic adjustment. A difference in sea level of 170 m is obtained from the two methods for the Cretaceous (80-100 m.y.B.P.). This is equivalent to a difference in continental flooding of 24 Mm 2, using the present-day hypsographic curve.We attempt to explain this difference firstly by allowing for the fact that the present-day ocean basins have more sediment in them than did the Cretaceous ocean basins. This produces a sea level change in the opposite direction to that produced by the reduction in mid-ocean ridge volume since the Cretaceous. Secondly, we suggest another large factor in producing the difference is that the present-day hypsographic curve is not the correct one to use when studying sea level stands in the Cretaceous. Present-day average continental heights are closely related to continental areas. Accepting this principle, if continents are joined together in the past, their average height must be greater, and so their hypsographic curve must be steeper. A given sea level rise would produce less continental flooding during times of continental aggregation than it would today.