or stomata, the tiny openings on the leaf surface through which plants absorb gases needed for photosynthesis, can provide clues to land elevation over time. Because these gas concentrations decrease with elevation, plants from higher elevations contain more stomata per square inch of leaf to capture them. The number of stomata on fossil leaves is thus an indicator of the amount of carbon dioxide and other gases in the air where the plant lived, according to a report in the December issue of Geology. That, in turn, provides a means of estimating land elevation with an average error of only 300 meters--significantly lower than the error rate intrinsic in other approaches to reconstructing paleoelevation.