Peter J. Smith
Department of Earth Sciences
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...