Satellite gravity inversion incorporating a lithosphere thermal gravity correction has been used to map crustal thickness and lithosphere thinning factor for the NE Atlantic. Predicted oceanic crustal thicknesses in the Norwegian Basin are between 4 and 7 km on the extinct Aegir Ridge, increasing to 9 -- 14 km at the margins, consistent with volcanic margin continental breakup at the end of the Paleocene. The observation (from gravity inversion and seismic refraction studies) of thin oceanic crust produced by the Aegir Ridge in the Oligocene may have implications for the temporal evolution of asthenosphere temperature under the NE Atlantic during the Tertiary. Thin Oligocene oceanic crust may imply cool (normal) asthenosphere temperatures during the Oligocene in contrast to elevated asthenosphere temperatures in the Paleocene and Miocene-Recent as indicated by the formation of volcanic margins and Iceland respectively.