The Paleobotanical Record (1998)

Richard A. Kerr's article “Comet shower hit, but life didn't blink” (News, 30 Jan., [p. 652][1]) reports on Kenneth Farley's interpretation of elevated helium-3 levels as an indicator of comet dust in Eocene ocean sediments and their temporal correlation to large impact craters and shocked quartz crystals. Helium values peaked at 35.5 million years ago (Ma) and tapered off over the 2 million years that followed. From these lines of evidence, experts are said to have concluded that, during this time, there was a terrestrial comet impact but, the article states, “What's missing is any sign that the shower affected life,” for the biota was left “unscathed.”

Although mass extinctions are not known from the paleobotanical record at this time, a major climatic cold snap—and consequent botanical change—did occur throughout North America about 34 to 33 Ma ([1][2]). This corresponds with the Eocene-Oligocene boundary ([2][3]) and the subsequent million years. The paleobotanical evidence thus suggests to me a climate-altering blow, with (i) an abrupt decrease in the mean annual temperature, (ii) an increase in the mean annual range of temperatures, and (iii) floras adapted to these colder temperature regimes ([1][2]).

1. [↵][4]1. H. D. MacGinitie
 , Carnegie Inst. Wash. Publ. 599 1 (1953);
 1. K. Hatai
 1. J. A. Wolfe, 2. D. M. Hopkins
 , in Tertiary Correlations and Climatic Changes in the Pacific, K. Hatai, Ed. (Sasaki, Sendai, Japan, 1967), pp. 67–76;
 1. J. A. Wolfe
 , Paleobot. Paleoecol. Evol. 2, 79 (1981);
 [OpenUrl][5]
 Am. Sci. 66, 694 (1978);
 [OpenUrl][6][GeoRef][7][Web of Science][8]
 1. S. L. Wing
 , Ann. Mo. Bot. Gard. 74, 748 (1987);
 [OpenUrl][9][CrossRef][10][Web of Science][11]
 1. D. R. Prothero, 2. W. A. Berggren
 1. J. A. Wolfe
 , in Eocene-Oligocene Climate and Biotic Evolution, D. R. Prothero, and W. A. Berggren, Eds. (Princeton Univ. Press, Princeton, NJ, 1992), pp. 421–436.
 

2. [↵][12]1. D. R. Prothero, 2. W. A. Berggren
 , Eds. Eocene-Oligocene Climate and Biotic Evolution (Princeton Univ. Press, Princeton, NJ, 1992).

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