The nature and composition of the Archean Mantle



In past decades, we have acquired a reasonable understanding of the workings of the modern earth, but our knowledge of how it got that way is extremely rudimentary. We know surprisingly little about how and when the continents, hydrosphere, core, and mantle came into being and evolved to their present state, and we have only the most fragmentary picture of the nature and tectonic operation of the young earth, despite a geological record which extends back at least to 3.8 Ga and probably to 4.3 Ga. One of the most fundamental and most interesting of the challenges left in earth science is the problem of understanding the tectonic and geochemical evolution of the Archean (pre-2.5-Ga-old) earth. In particular, attention must be focused on the evolution of the mantle, for this is the part of the earth from which the continents and probably much of the atmosphere originally segregated.