Introduction

As geochronology has progressed in the last 20 years, the Archean has continued to attract interest. Advancements in the understanding of Archean crustal and mantle evolution can be traced through a series of meetings and published papers beginning in 1970 with the first International Archean Symposium in Perth in Western Australia. Among the exciting problems at that meeting were the relationship between low and high grade Archean terrains, the origin of Archean ultramafic rocks and, in particular, the recently discovered komatiites in South Africa, and the origin of various Archean mineral deposits. Only about 30% of the papers dealt with geochronology and Archean crustal evolution. If one were to identify a landmark meeting for the Archean, it would almost certainly be the NATO Advanced Study Institute convened by Brian Windley in April of 1975 at Leicester. At this meeting, the Archean truly came of age. Investigators from many different disciplines focused their expertise on the early history of the earth. Exciting debate and discussion centered on such topics as the role of plate tectonics in the Archean, the relative importance of compressive versus vertical tectonics, and the use of trace elements in understanding both the origin and tectonic setting of Archean rocks.