View Full Version : Asteroid impacts on earth

Roger E. Moore
2018-Sep-30, 10:53 PM
Astroblemes are geology, too. This paper has a good overview on the most extreme impacts from around 2 billion years ago.


Chromium isotope evidence in ejecta deposits for the nature of Paleoproterozoic impactors

Berengere Mougel, Frederic Moynier, Christa Gopel, Christian Koeberl (Submitted on 20 Dec 2016)

Non-mass dependent chromium isotopic signatures have been successfully used to determine the presence and identification of extra-terrestrial materials in terrestrial impact rocks. Paleoproterozoic spherule layers from Greenland (Graenseso) and Russia (Zaonega), as well as some distal ejecta deposits (Lake Superior region) from the Sudbury impact (1,849 +/- 0.3 Ma) event, have been analyzed for their Cr isotope compositions. Our results suggest that 1) these distal ejecta deposits are all of impact origin, 2) the Graenseso and Zaonega spherule layers contain a distinct carbonaceous chondrite component, and are possibly related to the same impact event, which could be Vredefort (2,023 +/- 4 Ma) or another not yet identified large impact event from that of similar age, and 3) the Sudbury ejecta record a complex meteoritic signature, which is different from the Graenseso and Zaonega spherule layers, and could indicate the impact of a heterogeneous chondritic body.