McCall,G.J.H.(2009): Half a century of progress in research on terrestrial impact structures: A review. Earth-Science Reviews, 92, 99-116.


 The author, who investigated the Wolfe Creek, Australia, in 1962 and edited two Benchmark Sets of Readings on Meteorite Craters and possible Astroblemes in 1977 and 1979, reviews the state of knowledge at the present time. The text is concerned with terrestrial impact structures, geological features, without any consideration of extraterrestrial analogues. A handful of definitive publications are drawn on to present the story of terrestrial impact in a single article. The text covers historical aspects (briefly); the effect of target variations; the paucity of human observation of such large-scale events; distinction from volcanic (endogenous) structures; modification by geological processes; the transience of the crater initially formed on the target, and its subsequent modifications; the global geographic distribution of the 174 structure now listed (of which a number are dubious attributions); their distribution in geological time (many ages being known only known to wide limits, maximum or minimum values); their size distribution; calibrations of impact frequencies; shock effects; processes on impacts; the stages of formation; impact into shallow marine and deep sea targets; impacts on ice (about which little is known); and finally the input of impact into biotic extinctions. In this last lengthy section, the summaries of the conclusions of scientists researching impact on Earth and palaeontologists researching biotic impact are set side by side. It is concluded that, if the recent foraminiferal evidence obtained by Gerta Keller and associates is taken at its face value, the case of impact as a sole agent in extinction is non-existent: biotic extinction is clearly a complex process involving a number of causes, in some cases it was staggered in time, and different sets of organisms responded quite differently and surprisingly, even in the same extinction event. Extraterrestrial impact may have been one of the causes in some cases, but it may have been regional rather than global in its effects. We may never know how much input it had into the record of biotic extinction of Earth? An enormous amount of new knowledge has arisen from detailed studies of this new family of remarkable geological structures.

Keywords: impact structures; craters; shock metamorphism; geophysical investigations; biotic extinctions』

1. Introduction
2. Historical
3. Impacts on the Earth and extraterrestrial bodies: target variations on Earth
4. The paucity of human observation historically
5. Distinction from volcanic (endogenous) structures
6. Modification by geological processes
7. The terms ‘crater’ and impact structures: transient craters: morphology
8. Global distribution
9. Age dating of the impacts
10. Size distribution
11. Impact frequencies
12. Processes on impact
13. Shock effects
 13.1. Introduction
 13.2. Subsolidus shock effects
 13.3. Impact melting
 13.4. Trace additions from the impactor
 13.5. Volume of impact melt sheets
 13.6. Pseudotachylite
 13.7. Distribution of shock metamorphism
 13.8. Proximal and distal ejecta
14. Formation of impact structures
15. Geophysical investigation of impact structures
 15.1. Introduction
 15.2. Gravity
 15.3. Magnetism
 15.4. Seismic reflectance and refraction
 15.5. Electrical methods
16. Impacts into a marine environment
 16.1. Introduction
 16.2. The marine structures studied
17. Impacts onto ice
18. Impact structures and biological extinctions
 18.1. The K/T extinction
 18.2. Other extinctions
  18.2.1. Late Eocene impactoclastic layers (〜35 Ma)
  18.2.2. The Paleocene-Eocene boundary
  18.2.3. Cretaceous 〜74 Ma: the Manson Iowa structure
  18.2.4. The Cenomanian-Turonian boundary
  18.2.5. The Jurassic-Cretaceous boundary
  18.2.6. The early Toarcian
  18.2.7. The Triassic-Jurassic boundary (200 Ma)
  18.2.8. End-Permian (253 Ma)
  18.2.9. Late Guadalupian (North American stage of Late Permian)
  18.2.10. Devonian-Carboniferous (362.5 Ma)
  18.2.11. Late Devonian (367 Ma)
  18.2.12. Ordovician-Silurian boundary
  18.2.13. The earlier events
 18.3. Conclusion
19. Final discussion