The major scientific objective of the AMSOC project is to obtain samples of the upper part of the earth's mantle and to determine the nature of the Moho discontinuity. Boisse's analogy of 1850 suggesting that meteorites were a fair approximation of the composition of the earth's interior was a brilliant idea for its day, but is too inexact for present purposes.

Above the discontinuity is a layer commonly called the "crust" and generally considered to be basalt. It is extraordinarily uniform in thickness suggesting that its base represents a phase transition and that the Moho under the oceans might represent the level of some isotherm, or past isotherm, at which a reaction took place.

Above the "crust" is a layer of variable thickness and seismic velocity thought to be consolidated sedimentary or volcanic rocks. Finally one comes to the unconsolidated sediments of the ocean floor which are a few hundred meters thick and no doubt resemble the material obtained from shallow cores. In these last two layers one might hope to find fossils going far back in the history of the oceans and to derive from this record information of extraordinary scientific importance.

The following predictions are made.

(1) The mantle will be peridotite resembling the olivine nodules found in basaltic volcanoes and St. Paul's rock.

(2) The "basalt crust" will be serpentinized peridotite, hydrated mantle material.

(3) The Moho discontinuity represents a past isotherm above which serpentine was a stable phase.

(4) The sedimentary column will be very incomplete and have many great hiatuses.

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