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 glacialinterglacial cycles seen in sea cores. They are particularly rare in desert regions.
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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: 12451247.
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: 883-885.
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