When in 1981 Louis and Walter Alvarez, the father and son team,
unearthed a tell-tale Iridium-rich sedimentary horizon at the 65
million years-old Cretaceous-Tertiary boundary at Gubbio, Italy,
their find heralded a paradigm shift in the study of terrestrial
evolution. Since the 1980s the discovery and study of asteroid
impact ejecta in the oldest well-preserved terrains of Western
Australia and South Africa, by Don Lowe, Gary Byerly, Bruce
Simonson, Scott Hassler, the author and others, and the
documentation of new exposed and buried impact structures in
several continents, have led to a resurgence of the idea of the
catastrophism theory of Cuvier, previously largely supplanted by
the uniformitarian theory of Hutton and Lyell. Several mass
extinction of species events are known to have occurred in temporal
proximity to large asteroid impacts, global volcanic eruptions and
continental splitting. Likely links are observed between asteroid
clusters and the 580 Ma acritarch radiation, end-Devonian
extinction, end-Triassic extinction and end-Jurassic extinction.
New discoveries of 3.5 3.2 Ga-old impact fallout units in South
Africa have led Don Lowe and Gary Byerly to propose a protracted
prolongation of the Late Heavy Bombardment ( 3.95-3.85 Ga) in the
Earth-Moon system. Given the difficulty in identifying asteroid
impact ejecta units and buried impact structures, it is likely new
discoveries of impact signatures are in store, which would further
profoundly alter models of terrestrial evolution..
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