This figure compares the Hallam et al. (1983) and Exxon eustatic (global) sea level reconstructions for the Phanerozoic eon. The Exxon curve [1] is a composite from several reconstructions published by the Exxon corporation (Haq et al. 1987, Ross & Ross 1987, Ross & Ross 1988). Both curves are adjusted to the 2004 ICS geologic timescale.

Hallam et al. and Exxon use very different techniques to measuring global sea level changes. Hallam's approach is qualitative and relies on regional scale observations from exposed geologic sections and estimates of the areas of flooded continental interiors. Exxon's approach relies on the interpretation of seismic profiles to determine the extent of coastal onlap in subsequently buried sedimentary basins. Hallam is insensitive to rapid fluctuations in sea level. Exxon is sensitive to rapid fluctuations but tends to overinterpret local geologic changes resulting in bias towards reporting unphysical rapid fluctuations.

The depth scale is as reported by Exxon. Because Hallam is reported as qualtitative (i.e. uncalibrated), these sea level changes were scaled to match the Exxon record during the period 0-250 Myr.

A black bar is added to indicate the scale of sea level fluctuations during the last glacial/interglacial transition. This change occurred purely within the last 20 kyrs, and note that neither system of measurements is capable of resolving changes on this time scale. It also should be noted that very rapid fluctuations of similar scale are potentially possible during all periods during which large scale ice sheets are present (see: Phanerozoic climate change).

On the scale of this figure, the melting of all existing ice sheets would result in a sea level rise of ~80 meters. Changes on larger scales, which evidently occurred many times in the past, are the result of geologic changes in the structure of ocean basins. Essentially, such changes affect the average depth of the oceans relative to the continents.