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Extraterrestrial Cause for the Cretaceous-Tertiary Extinction
A hypothesis is suggested which accounts for the extinctions and the iridium observations, and the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other. Expand
Spheroids at the Cretaceous-Tertiary boundary are altered impact droplets of basaltic composition
Sand-size spheroids of K-feldspar in the Cretaceous-Tertiary (C-T) boundary clay at Caravaca, southern Spain, were interpreted by Smit and Klaver as having solidified from a melt resulting from theExpand
Iridium Anomaly Approximately Synchronous with Terminal Eocene Extinctions
The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago, and other workers have deduced that the microtekkites are part of the North American strewn tektite field, which is dated at about34 million years before present. Expand
Current status of the impact theory for the terminal Cretaceous extinction
Iridium is depleted in the earth's crust relative to its normal solar system abundance. Several hundred measurements by at least seven laboratories have disclosed an iridium abundance anomaly at theExpand
The Precursor of the Cretaceous-Tertiary Boundary Clays at Stevns Klint, Denmark, and DSDP Hole 465A
The mixed-layer smectite-illite from the interval 118 to 120 centimeters in the zone of high iridium abundance has a very low rare earth element content; the negative cerium anomaly indicates formation in the marine environment. Expand
Experimental evidence that an asteroid impact led to the extinction of many species 65 million years ago.
  • L. W. Alvarez
  • Geology, Geography
  • Proceedings of the National Academy of Sciences…
  • 1 September 1982
An overview is presented of the theory that an asteroid hit the earth 65 million years ago wiping out large numbers of land and marine species, and the transport mechanism of the dust created by the impact and four mechanisms for the extinction of species are discussed. Expand
Impact Theory of Mass Extinctions and the Invertebrate Fossil Record
The paleontological record bears witness to terminal-Cretaceous extinctions on two time scales: a slow decline unrelated to the impact and a sharp truncation synchronous with and probably caused by the impact. Expand
The End of the Cretaceous: Sharp Boundary or Gradual Transition?
Evidence indicates that the Cretaceous-Tertiary boundary is very sharp, and, within the limits of resolution, it is apparently synchronous at the various boundary localities. Arguments to theExpand
Mass extinctions caused by large bolide impacts.
Evidence indicates that the collisions of Earth and a large piece of Solar System debris caused the great extinctions of 65 million years ago, leading to the transition from the age of the dinosaurs to theAge of the mammals. Expand
Geochemical anomalies near the Eocene/Oligocene and Permian/Triassic boundaries
Evidence is presented to support the theory that several mass extinctions, i.e., those that define the Permian-Triassic boundary, the Cretaceous-Tertiary boundary, and the Eocene-1 OligoceneExpand