The Collaborative International Dictionary of English v.0.48:

earth-shaking \earth-shaking\ adj.
   sufficiently significant to affect the whole world; as,
   earth-shaking proposals; an earth-shaking event.

   Syn: world-shaking, world-shattering(predicate), world
        shattering(predicate).
        [WordNet 1.5]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "earthshaking":
   big, big-league, big-name, big-time, bigwig, bigwigged, booming,
   consequential, considerable, deafening, double-barreled,
   ear-piercing, ear-rending, ear-splitting, forte, fortissimo, full,
   grand, great, heavyweight, high-powered, important, loud,
   loud-sounding, loudish, major, material, momentous, name, pealing,
   piercing, plangent, resounding, ringing, self-important,
   significant, sonorous, stentoraphonic, stentorian, stentorious,
   substantial, superior, thunderous, tonitruant, tonitruous,
   window-rattling, world-shaking