| Subject: paleoelevation |
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blobrana
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Date Posted: 10:40:50 11/30/04 Tue
A novel way has been developed, to determine land elevation throughout geological ages. Knowing how high mountains and plateaus were in the past can help scientists to study how our climate system evolved.
"Understanding the past elevation of land surfaces, also known as paleoelevation, has been one of geology's Holy Grails. This is the first paleobotanical method that works globally and is independent of long-term climate change. The new method will help us to understand the rate at which some of the Earth's most important mountains have uplifted. It will also show how the process of mountain building influenced climatic patterns as well as plant and animal evolution."
The new method of paleoelevation involves counting the stomata on leaves of plants going back as far as 65 million years ago. Stomata are minute openings on the surface of leaves through which plants absorb gases, including carbon dioxide, which plants need for photosynthesis.
If you climb to higher elevations, carbon dioxide is less concentrated. Therefore, the higher the elevation, the more stomata per square inch of leaf surface a plant would need to survive. By simply counting the number of fossil stomata, Dr. McElwain, a Field Museum scientist, estimated how much carbon dioxide was in the air when the fossil leaf developed. From that, she estimated the elevation at which the fossil plant once lived.
She used historical and modern collections of Quercus kelloggii (California Black Oak) leaves for her study, because the tree grows within an unusually wide range of elevations from 60 to 2,440 meters.
The historical leaves were collected by botanists in the 1930s and stored within herbarium collections of the Field Museum and the University of California, Berkeley.
This new method of estimating land elevation has an average error of about 980 feet (300 meters) – but as low as 330 feet (100 meters). Such an error rate is much lower than the error rate of existing paleoelevation methods, all of which have significant limitations. This method can be used for any area where suitable plant specimens can be found.
High mountains and plateaus can act as important barriers to plant and animal migration and dispersal resulting in isolation of plant and animal populations on opposite sides of mountain chains.
Therefore, knowing exactly when in the geological past the mountains of today's world reached their current elevations is relevant to our understanding of plant and animal evolution since isolation is an important mechanism in the formation of species.
In addition, high mountains and large plateaus (such as those in Tibet and Colorado today) have always had a big influence on climate by altering patterns of atmospheric circulation.
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