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The submarine hydrothermal activity on and near the Galápagos Rift has been explored with the aid of the deep submersible Alvin. Analyses of water samples from hydrothermal vents reveal that hydrothermal activity provides significant or dominant sources and sinks for several components of seawater; studies of conductive and convective heat transfer suggest that two-thirds of the heat lost from new oceanic lithosphere at the Galápagos Rift in the first million years may be vented from thermal springs, predominantly along the axial ridge within the rift valley. The vent areas are populated by animal communities. They appear to utilize chemosynthesis by sulfur-oxidizing bacteria to derive their entire energy supply from reactions between the seawater and the rocks at high temperatures, rather than photosynthesis.

Radiocarbon dates for Vermetidae limestone from the edge of the Brazilian Shield at Cape San Agostinho, Brazil, indicate sea level stands of up to 2.60 meters above the present position, 3660, 2790, and 1190 years ago. Accurate determination of relative sea level is possible because of the well-defined habitat of the fossils dated.

A geomagnetic profile across the northern South Atlantic yields spreading rates for the last 70 m.y. which vary from 1.6 to 2.0 cm/year. There is evidence for three regional discontinuities in the spreading history of the South Atlantic.

In October 1964, a detailed geophysical and sampling survey was made of the central part of the Mid-Atlantic Ridge between 22 degrees and 23 degrees north latitude. The results indicate a large difference in age between the relief of the crest and that of the flanks of the Ridge and suggest that the crest portion is very young. Detailed surveys of two sediment-filled valleys on the upper western flank of the Ridge reveal different sedimentary sequences in the two valleys and indicate the probable existence of a locally controlled depositional regime and a significant local supply of sediment.