Crustal Formation in the Hadean

Surface conditions were initially hostile on Earth as the planet was covered by a magma ocean and frequently struck by giant meteorites. The question remains: When did Earth become habitable? The lack of a rock record from Earth’s first 600 Ma of history has hindered our understanding of crust formation and only detrital zircon from that period provide a direct record of those early events. Until recently, our understanding of the Hadean was mainly based on a single location with abundant Hadean zircon, the Jack Hills region in Western Australia. I’m part of a group of researchers that recently discovered a new location of abundant Hadean detrital zircon in the Green Sandstone Bed (GSB) in the 3.6 to 3.2 Ga Barberton greenstone belt (BGB), South Africa (Byerly et al., 2018). Unlike the well-known Jack Hills locality, the GSB experienced low metamorphic grade (lower greenschist), is largely unstrained, and open to study from the micron- to the outcrop-scale.

4.2 to 3.3 Ga detrital zircons from the Green Sandstone Bed

Evolution of Early Life

The habitability of Earth may have been severely affected by large meteorite impacts, especially during the Late Heavy Bombardment from 4.0 to 3.8 Ga. Research over the last 30 years of the terrestrial Archean impact record has shown that giant impacts continued until the late Archean. To date, eight such meteorite impact events (20 - 70 km bolide diameter) have been discovered in the BGB. I’m interested in understanding the effects of these large impacts on the surface environment and, consequently, the early biosphere. Currently, I am studying the δ13C signature and sedimentology of marine banded cherts across the 3.26 Ga S2 impact horizon in the Barberton greenstone belt.

3.26 Ga banded chert

Crustal settings and nature of tectonic uplifts in the Archean

The formation of continents and initiation of plate tectonics caused substantial changes to the atmosphere, hydrosphere, and, consequently, the biosphere. A decades-long dispute in the study of the earliest preserved rock sequences concerns whether they developed on older, evolved continental crust or whether they formed as mainly mafic to ultramafic terranes with small inclusions of felsic rocks. Similarly, the nature of tectonic processes in the early Archean is still highly debated: we don’t even know yet if the geodynamic system involved plate tectonics or some other form of crustal process. New developments in provenance analyses coupled with stratigraphic techniques have been underutilized in resolving these kinds of problems although they are routinely applied to Phanerozoic systems. I use multiproxy analyses for regional basin reconstructions by combining stratigraphic and provenance analyses with zircon geochemistry (εHf, δ18O, and trace element geochemistry) to constrain the tectonic setting and crustal processes recorded in one of the oldest exposed siliciclastic basins on Earth, the 3.28 to 3.23 Ga Fig Tree basin.