1 Desert Varnish -- A Record Of Desert Climate Too Good To Be True. NATS 104 Fall Semester, 2010 A. Good Student During the 1980s and 1990s a new technique provided ancient records of climate-change in the world's deserts, but it was just too good to be true. "Desert varnish" -- a dark coating of rocks in deserts -- was first explained as a microbial deposit by Dorn and Oberlander (1981). Next, desert varnish was used as a dating method (Dorn, 1983), and eventually microscopic layers of desert varnish were studied (Dorn, 1984) showing the same climate oscillations as the deep-sea cores. However, no other scientist successfully used the techniques and the results were never duplicated. Finally, scientists dating desert varnish samples published evidence that the samples were not from desert varnish (Beck et al., 1998), and they were sued by the desert varnish investigator (Malakoff, 1998, 1999). Most records of long-term (millions of years) climate change are from the sea floor. There, sediment accumulates slowly and steadily, and cores of sea-floor sediment contain a variety of fossils and isotopes that document cyclical oscillations tied to glacial advances and retreats over the last two and one-half million years (Imbrie and Imbrie, 1979). Records from on land are precious because they provide a check on the timing and magnitude of the glacial-interglacial cycles seen in sea cores. They are particularly rare in desert regions. Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body2 Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Body Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Conclusion Works Cited Beck, W., Donahue, D. J., Jull, A. J. T., Burr, G., Broecker, W. S., Bonani, G., Hajdas, I. and Malotki, E. 1998. Ambiguities in direct dating of rock surfaces using radiocarbon measurements. Science 280: 2132 - 2139. Dorn, R. I. 1983. Cation-ratio dating: a new rock varnish age-determination technique. Quaternary Research 20: 49-73. Dorn, R. I. 1984. Cause and implications of rock varnish microchemical laminations. Nature 310: 767-770. Dorn, R. I. and Oberlander, T. M. 1981. Microbial origin of rock varnish. Science 213: 1245-1247. Imbrie, J. and Imbrie. K. P. 1979. Ice Ages: solving the mystery. Enslow Publ., Hillside, New Jersey, 224 p. Malakoff, D. 1998. rock dates thrown into doubt, researcher under fire Science 280: 2041-2042. Available from http://www.sciencemag.org/cgi/content/full/280/5372/2041. Accessed September 25, 2003. Malakoff, D. 1999. Cleared of misconduct, geoscientist sues critics. Science 286: