Donald R. Lowe, Gary R. Byerly; Early Archean silicate spherules of probable impact origin, South Africa and Western Australia. Geology ; 14 (1): 83–86. doi: https://doi.org/10.1130/0091-7613(1986)14<83:EASSOP>2.0.CO;2
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Layers of sand-sized silicate spherules in 3.2 to 3.5 Ga Archean greenstone belts in South Africa and Western Australia formed by the accumulation of quenched liquid silicate droplets having primary compositions resembling those of immediately underlying rock sequences. The layers and particles appear to be unrelated to volcanic activity, and we suggest that both occurrences may represent melt droplets formed during meteorite or comet impacts. If so, these spherules are the oldest known terrestrial impact products. If these objects are representative of a larger population of early Archean impact features, it may be possible to directly estimate the meteorite flux on the early Archean earth.