Ultra-Deep Drilling through 3.5-Billion-Year-Old Crust in South Africa

Abstract

The Makhonjwa Mountains of South Africa and Swaziland comprise some of the most sought-after geo-real estate in the world. It is priceless—that is, for geoscientists—because the rocks of this approximately 120 km by 60 km corner of southern Africa, also known as the Barberton Greenstone Belt, date back to 3.2–3.6 billion years (Ga), representative of Earth in early Archean times when it was still ~1 Ga years young. They are not the very oldest rocks on Earth (those occur in Greenland and Canada), but they are the oldest best-preserved ones; thus, this stretch of land is without equal for research into the early history of our Earth. It is home to some of the earliest fragments of island arc, oceanic crust, and vestigial tracts of continent covered with sedimentary and volcanic rocks. So well-preserved are these rocks that unless one radiometrically dates them, it is near impossible to distinguish them from many modern rocks. This exceptional preservation has ensured that the Makhonjwa rocks yield the oldest directly dated and undisputed signs of life on Earth, and compared to our present biosphere they also provide detailed clues about the hostile nature of the paleoenvironments under which this life struggled to persist. One severe challenge entailed coping with more potent solar radiation to which life is particularly sensitive, when Earth’s magnetic field was too weak to efficiently shield the surface from the relentless solar wind of lethal charged particles. Another is to explore for paleo-suture zones that can help establish when plate tectonics first emerged as the dominant solid earth recycling process to nurture the only sustainable habitable zone in our solar system. These then represent some of the targets of a new deep drilling project, on which an ICDP workshop was focused and held on 13–19 April 2010.