No. 96: Nov-Dec 1994
During our latest anomaly-collecting cycle, we came across two reports on apparently identical phenomena. Neither article mentioned the work of the other!
Both groups of scientists processed massive quantities of earthquake records to form "seismic images" of structures deep in the bowels of the earth. (The technique is called "seismic tomography.") Both groups have discerned huge slabs of crust that were once on the planet's surface but were subsequently thrust ("subducted") down under the continents. These slabs are now hundreds of kilometers below the surface, and they have dragged water along with them. In fact, their water inventories may rival today's surface oceans; they may even have been surface oceans themselves millions of years ago before they descended into the infernal regions.
Only a few years ago, all geologists maintained that all water in subducted slabs was squeezed out of the rocks by immense pressure and later reappeared at the surface as volcanic steam.
Deep ocean #1. G. Nolet and A. Zielhuis, Princeton seismologists, report a huge reservoir of water about 900 kilometers under present-day Europe. Some 400-500 million years ago, there was an ocean in this locale.
(Zimmer, Carl; "The Ocean Within," Discover, 15:20, October 1994.)
Deep ocean #2. H. Wysession, Washington University, has located a water-rich slab 250 kilometers thick at a depth of 2,700 kilometers under Indonesia. He thinks it might be the subducted floor of the paleo-ocean Tethys that last saw sunlight 250 million years ago.
(Redfern, Martin; "Lost Ocean Found Deep in the Earth," New Scientist, p. 16, September 3, 1994.)
Reference. Anomalies of the earth's core and mantle are covered in our catalog volume: Inner Earth. Details here.