Lightning as a fractal aggregation process is one of the natural
fractal observables:
http://www.sciencenews.org/articles/20070217/fob5.asp
Fast & Free Delivery
Science News Online
Week of Feb. 17, 2007; Vol. 171, No. 7
Stroke of Good Fortune: A wealth of data from petrified lightning
Sid Perkins
The lumps of glass created when lightning strikes sandy ground can
preserve information about ancient climate, new research indicates.
a8165_1749.jpg
BOLT FROM THE BLUE. When lightning strikes the ground, it fuses sand in
the soil into tubular masses of glass called fulgurites (top). The gases
trapped in bubbles in that glass (bottom) yield clues to ancient soil
and atmospheric chemistry and climate.
L. Carion/Carion Minerals, Paris; Navarro-González
Worldwide, lightning flashes occur about 65 times per second. Each bolt
releases as much energy as is stored in a quarter-ton of TNT. The flash
heats the air to about 30,000°C, about five times the temperature of the
surface of the sun. If that electrical discharge strikes sandy ground,
it can melt and then fuse sand and other materials into masses of glass
called fulgurites, says Rafael Navarro-González, a geochemist at the
National Autonomous University of Mexico in Mexico City. Those masses
take their name from fulgur, the Latin word for lightning.
Although thunderstorms are common in many parts of the world, they're
rare in the desert of southwestern Egypt. "Satellite data gathered
between 1998 and 2005 detected little, if any, lightning in that area,"
says Navarro-González. However, the lumps and tubes of glass that litter
the region's shifting dunes are proof that lightning, the only source of
fulgurites, frequently touched down there in the past.
Studying samples of a fulgurite that had been collected in 1999,
Navarro-González and his colleagues found that it had formed 15,000
years ago. The team measured the luminescent glow that the fulgurite's
minerals gave off when heated. Over time, exposure to cosmic rays and to
the decay of radioactive elements in the soil produce defects in the
material. The more defects, the brighter the heated material glows.
Chemical analyses of the gases trapped in bubbles inside the glass
revealed that there have been major changes in the ancient landscape.
Today, it's bare sand, but 15,000 years ago, it was hospitable to shrubs
and grasses.
The tests, which are the first to look at the chemical composition of a
fulgurite's gas bubbles, revealed a small amount of argon, the
atmosphere's most abundant inert gas today. In an average modern sample
of Earth's atmosphere, argon outweighs carbon dioxide about 25:1. In the
fulgurite gases, however, carbon dioxide was more than 100 times as
common as argon, says Navarro-González. That extra carbon dioxide was
generated when the lightning bolt vaporized organic material in the
once-fertile soil, the researchers propose in the February Geology.
The ratio of carbon-12 to carbon-13 isotopes that the team measured in
the trapped gases is typical of that generated by the photosynthesis of
grasses and shrubs adapted to hot, arid climates. Today, such vegetation
grows in southwestern Niger, about 600 kilometers south of the site
where the team's fulgurite was recovered. The ratios of elements in
fulgurite's gases were typical of those in the modern soils of that
region.
All these clues suggest that 15,000 years ago, near the end of the most
recent ice age, the climate in southwestern Egypt was similar to that
found today in Niger.
Because fulgurites are mainly glass, they're chemically stable and
aren't very susceptible to erosion, says Barbara Sponholz, a physical
geographer at the University of Würzburg in Germany. That makes
fulgurites and the gases that they contain long-lasting indicators of
climate, she notes.
Analyzing the Egyptian fulgurites is "an interesting way of showing that
the climate in this region has changed," agrees Kenneth E. Pickering, an
atmospheric scientist at NASA's Goddard Space Flight Center in
Greenbelt, Md.
Letters:
Finding CO2 levels that are 2,500 times higher in 5,000-year-old
fulgurites than in modern samples, scientists have speculated that the
extra CO2 resulted from vaporization of organic material by lightning.
Could some of this gas reflect elevated atmospheric CO2? And if so,
could current laments regarding "unprecedented levels" of CO2 be
insupportable?
John M. Corboy
Mililani, Hawaii
Other archives of preindustrial carbon dioxide, such as ice cores and
corals, don't indicate that concentrations of the greenhouse gas were
abnormally high 5,000 years ago.—S. Perkins
If you have a comment on this article that you would like considered for
publication in Science News, send it to editors@[EMAIL PROTECTED]
Please
include your name and location.
ScienceNews.org needs your input
Take our quick, 1-minute survey, and tell us how to improve our Web site.
You might win a free iPod! .
To subscribe to Science News (print), go to
https://www.kable.com/pub/scnw/
subServices.asp.
To sign up for the free weekly e-LETTER from Science News, go to
http://www.sciencenews.org/pages/subscribe_form.asp.
References:
Navarro-González, R., et al. 2007. Paleoecology reconstruction from
trapped gases in a fulgurite from the late Pleistocene of the Libyan
Desert. Geology 35(February):171-174. Abstract available at
http://geology.geoscienceworld.org/cgi/content/abstract/35/2/171.
Further Readings:
A version of this article written for younger readers is available at
Science News for Kids.
Sources:
Rafael Navarro-González
Institute of Nuclear Sciences
National Autonomous University of Mexico
Apartado Postal 70-543
Mexico D.F. 04510
Mexico
Kenneth E. Pickering
NASA/Goddard Space Flight Center
Atmospheric Chemistry and Dynamics Branch
Code 613.3
Greenbelt, MD 20771
Barbara Sponholz
Department of Geography
University of Würzburg
Am Hubland
D-97074 Würzburg
Germany
http://www.sciencenews.org/articles/20070217/fob5.asp
From Science News, Vol. 171, No. 7, Feb. 17, 2007, p. 101.
Copyright (c) 2007 Science Service. All rights reserved.
|
