Peter J. Smith
Department of Earth Sciences
Open University
Milton Keynes, U.K.
An analysis of trace elements in three Chinese Permian-Triassic (P-Tr) boundary sections reveals no enhancement of iridium, thus offering no support for the idea that the P-Tr mass extinctions were due to bolide impact. On the contrary, other trace element concentrations indicate intense volcanism at that time.
L. Zhou, F.T. Kyte, "The Permian-Triassic boundary event: A geochemical study of three Chinese sections," Earth and Planetary Science Letters, 90 (4), 411-21, 25 November 1988.
The 40Ar/39Ar dating of melt rocks from the submarine Montagnais impact crater southeast of Nova Scotia suggests that the impact occurred about 5 million years ago. The crater is therefore associated neither with the Cretaceous-Tertiary mass extinctions (65 My ago) nor the North American tektite field (35 My).
R. Bottomley, D. York, "Age measurement of the submarine Montagnais impact crater," Geophysical Research Letters, 15 (12), ...
