gems, geology, East Africa, Gondwana, Detrital zircons, Tectonics, Cambrian Explosion, John Saul

The explosive radiation of animals on Earth during the late Early Cambrian period (∼530–510 Ma) coincides with the deposition of enormous volumes of continentally derived sedimentary rocks throughout Gondwana. Quartz-rich sedimentary units collected from five continents display remarkably similar detrital-zircon U–Pb age patterns and are proposed to have been sourced from either side of a >8000 km-long and generally >1000 km-wide mountain chain (the Transgondwanan Supermountain), which formed following oblique collision between East and West Gondwana beginning at ∼650 Ma. The depositional system supplied by this mountain chain was >100 km³, equivalent to covering all 50 states of the USA with ∼10 km of sediment, and it lasted for at least 260 Myr. The enormous size of the vegetation-free mountain chain, its position near the equator, dramatic changes in global plate motion after the cessation of continent–continent collision, and the possible appearance of biota in soils that promoted rapid chemical weathering, resulted in extreme erosion and sedimentation rates that may be the highest in the geological record. This produced an unprecedented flux of P, Fe, Sr, Ca, and bicarbonate ions into the oceans. The addition of Sr raised seawater ⁸⁷Sr/⁸⁶Sr to the highest levels in Earth’s history, while P and Fe provided essential nutrients that supported a bloom of primitive life, in turn fueling the Cambrian explosion of animals. The influx of Ca and bicarbonate ions increased CaCO₃ supersaturation in the oceans, enabling species in numerous phyla to simultaneously develop skeletons.