Twenty-three SEASAT altimeter profiles crossing the Ascension fracture zone are used together with seafloor ages inferred from a kinematic model to estimate a geoid slope-age relation between ages of 5 snd 50 Ma. The data do not definitely contradict a half space cooling model (slope =-9.5¿3 cm/Ma) if biases are accepted, resulting in large scatter. However the data would seem to support a puzzling explanation in terms of a plate cooling model involving two distinct thermal thicknesses, one of ≈70 km for ages 35 Ma. Although preliminary, this result is similar to that found in the Pacific with a much larger data set. ¿American Geophysical Union 1987