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Ancient-air idea may not hold water.

Ancient-air idea may not hold water

Several independent teams of chemists are questioning promising claims made last year that amber -- a fossilized resin from trees -- can preserve samples of iar from the age of the dinosaurs and even farther in the past. Backed by experimental evidence, these researchers assert in the Aug. 5 SCIENCE that amber is permeable to gases and therefore cannot contain air for millions of years.

The term amber refers to a variety of chemically different resins excreted by certain species of coniferous trees. Before it hardens, the sticky resin can trap insects and larger animals such as frogs -- a property exploited by paleontologists who study the preserved animals (SN: 9/26/87, p.205).

Last year Robert A. Berner from Yale University and Gary P. Landis from the U.S. Geological Survey in Denver reported they had analyzed gas released by crushing amber samples to determine the oxygen content of the atmosphere from the time the resin oozed out of its tree. Amber from the Cretaceous period, approximately 85 million years old, indicated that oxygen made up 30 percent of the air during the age of the dinosaurs as compared with 21 percent of today's atmosphere, they concluded (SN: 11/7/87, p.293). Berner and Landis asserted that bubbles within the amber samples had trapped and preserved the air, providing scientists with a unique way of analyzing the atmosphere from millions of yers ago.

Several months later, Harmon Craig and Yoshio Horibe of the Scripps Institute of Oceanography in La Jolla, Calif., reported that their experiments indicated that while amber did indeed preserve ancient gases, these gases could not be viewed as representative of what was in the atmosphere (SN: 1/2/88, p.8).

Leading off the technical comments in SCIENCE, Harold B. Hopfenberg, a chemical engineer at North Carolina State University in Raleigh, and his colleagues report that their experiemnts demonstrate amber cannot trap air. Hopfenberg found amber readily absorbs propane, a molecule much larger than oxygen or nitrogen, the principal components of air. This means air can pass through amber's amorphous resin matrix, which resembles the plastics used as containers of carbonated beverages. Hopfenberg says. As an example of this kind of diffusion, he points out that bottles of unopened soda lose their fizz after a while on the shelf.

In a reversal of their former position, Horibe and Craig also report that air diffuses into amber and that any gas in amber cannot be as old as claimed by Berner and Landis. Amber chemist Curt W. Beck from Vassar College in Poughkeepsie, N.Y., writes that whether or not amber is permeable, the resin will react with any enclosed gas and will therefore alter it, a process dismissed by Berner and Landis.

In their response, Berner and Landis claim amber is much less permeable than the critics contend. They suggest that since Hopfenberg was analyzing microscopic chips of amber, the results of the diffusion experiment may not be reliable. While they are planning a different experiment to measure the permeability of amber, Landis says he is "90 percent certain" amber can preserve ancient air and provide information about oxygen levels through geologic time.
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Title Annotation:amber may be permeable to gases
Publication:Science News
Date:Aug 27, 1988
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