Abstract
This article presents a current (as of September 2019) list of recommended ages for proven terrestrial impact structures (n = 200) and deposits (n = 46) sourced from the primary literature. High-precision impact ages can be used to (1) reconstruct and quantify the impact flux in the inner Solar System and, in particular, the Earth–Moon system, thereby placing constraints on the delivery of extraterrestrial mass accreted on Earth through geologic time; (2) utilize impact ejecta as event markers in the stratigraphic record and to refine bio- and magneto-stratigraphy; (3) test models and hypotheses of synchronous double or multiple impact events in the terrestrial record; (4) assess the potential link between large impacts, mass extinctions, and diversification events in the biosphere; and (5) constrain the duration of melt sheet crystallization in large impact basins and the lifetime of hydrothermal systems in cooling impact craters, which may have served as habitats for microbial life on the early Earth and, possibly, Mars.
Highlights
Impact cratering is a fundamental process in the Solar System, shaping asteroids, planets, and their satellites (e.g., Baldwin, 1971; Shoemaker, 1983; Melosh, 1989; Ryder, 1990; French, 1998, 2004; Canup and Asphaug, 2001; Kring and Cohen, 2002; Osinski and Pierazzo, 2012)
High-precision impact ages can be used to (1) reconstruct and quantify the impact flux in the inner Solar System and, in particular, the Earth–Moon system, thereby placing constraints on the delivery of extraterrestrial mass accreted on Earth through geologic time; (2) utilize impact ejecta as event markers in the stratigraphic record and to refine bio- and magnetostratigraphy; (3) test models and hypotheses of synchronous double or multiple impact events in the terrestrial record; (4) assess the potential link between large impacts, mass extinctions, and diversification events in the biosphere; and (5) constrain the duration of melt sheet crystallization in large impact basins and the lifetime of hydrothermal systems in cooling impact craters, which may have served as habitats for microbial life on the early Earth and, possibly, Mars
All of the older Rb–Sr ages for terrestrial impact structures (e.g., Reimold et al, 1981) have been superseded by more robust U–Pb and/or Ar–Ar ages and, none of the original Rb–Sr results is recommended as best-estimate ages in this summary (Table 1)
Summary
Impact cratering is a fundamental process in the Solar System, shaping asteroids, planets, and their satellites (e.g., Baldwin, 1971; Shoemaker, 1983; Melosh, 1989; Ryder, 1990; French, 1998, 2004; Canup and Asphaug, 2001; Kring and Cohen, 2002; Osinski and Pierazzo, 2012). Bucher’s (1936) early work on the country’s ‘‘cryptoexplosion structures’’ probably remains the most recent systematic review of its kind; many impact structures in the United States were included in the more general listings of Freeberg (1969), Classen (1977), and Grolier (1985), and a website project maintained by Beauford (2019) provides basic information and the relevant literature for almost all impact structures and crater fields recognized in the country.] Nor does this relatively short summary provide an in-depth explanation and discussion of the isotopic methods commonly used to determine impact ages, such as the U–Pb and Ar–Ar geochronometers. This work presents a referenced source for current best-estimate ages that can be listed in online impact databases, such as the Earth Impact Database (hosted at the University of New Brunswick, Fredericton, Canada), which has recently been complemented by the database Impact Earth maintained by Osinski and Grieve (2019)
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