In accordance with the plate-tectonic theory, ophiolites are relict fragments of an oceanic crust, and the formation of eclogites, rocks generated at high pressures and at great depths, is related to convergent – subduction and collision processes at the ocean-continent boundary followed by their exhumation on the earth surface. The mechanisms of formation of the earth crust that involve plate-tectonic processes are now being revealed reliably for the Phanerozoic and Late Precambrian. What are the processes that gave rise to the earth crust in Early Precambrian time, at the early stages in the Earth's evolution? It is one of the most acute problems in modern geology. Arguments in favour of the ophiolitic nature of a mafic and ultramafic rock complex in the Central Belomorian greenstone belt of the Belomorian Mobile Belt and, to a greater extent, the world's first finding of the Earth's oldest 2720 Ma Archean eclogites suggest that in Early Precambrian time there also existed conditions that favoured plate-tectonic processes. These unique rocks are characterized in the paper both geologically and petrologically.