-Caveat Lector- <http://www.nature.com/nsu/010315/010315-9.html> Fall put leaves on trees JOHN WHITFIELD A carbon dioxide slump put leaves on the trees For the first 40 million years of their existence, land plants didn't bother to make leaves ‹ just green stems and small, spiny protrusions. Leaves only evolved, researchers now suggest, when a drop in the amount of carbon dioxide in the atmosphere meant that the benefits of intercepting more light began to outweigh the dangers of overheating. >From living and fossil plants, and geochemical information about past environments, David Beerling, of the University of Sheffield, UK, and colleagues have reconstructed the period when leafiness became a viable lifestyle1. "We don't really know why leaves evolved," says Paul Kenrick, a plant palaeontologist at London's Natural History Museum, "nobody's thought of carbon dioxide as being a factor in leaf evolution before." The amount of carbon dioxide in the atmosphere is reflected in the number of 'stomata' that plants produce. Stomata are the pores that let gases in and out, and out of which water evaporates, cooling the plant. The earliest plants had very few stomata. This served them well in a carbon dioxide-rich atmosphere, and helped to stop them drying out. Any leaves produced by such non-porous plant life would have quickly perished from overheating, Beerling's team calculate. Leafless plants, though, were preparing the world for their successors: about 380 million years ago, plants seems to have brought about a 90% drop in the atmospheric concentration of carbon dioxide. Plants lock up carbon in their woody tissues and roots, and by breaking up rocks, increasing the rate at which carbon passes out of the atmosphere. The new atmosphere changed the economics of photosynthesis. Plants developed lots of stomata ‹ making them better at taking up carbon dioxide, and at staying cool. Branched green stems became webbed, and highly divided, blade-like leaves developed, from which one-piece leaves quickly followed. Hand-in-hand with leaf evolution came sophisticated systems to transport water through the plant. This better plumbing may also have allowed plants to increase in size and complexity. Although the new leafy plants had to work harder to get carbon dioxide, they could capture more solar energy without overheating. So plant productivity increased, and animal life would have had more food. Of course, it's hard to know what the world was like 400 million years ago, harder still to work out how the life of the time adapted to it. "We are assuming that modern and ancient plants had the same responses," Beerling admits. Stomata and plants' responses to carbon dioxide seem not to have changed much in the past 400 million years: today, plants are making fewer stomata in response to the increased carbon dioxide in the atmosphere. Kenrick comments that, with more and better plant fossils from between 410 and 370 million years ago, researchers should be able to back up the relationship between leaves and carbon dioxide, or to shoot it down. One would expect, for example, to see leaves first appear in plants from cooler, temperate regions, where overheating is less of a danger. The ball, says Kenrick, is now in the fossil-hunters' court. ================================================================= Kadosh, Kadosh, Kadosh, YHVH, TZEVAOT FROM THE DESK OF: *Michael Spitzer* <[EMAIL PROTECTED]> ~~~~~~~~~~~~~~~ The Best Way To Destroy Enemies Is To Change Them To Friends ================================================================= <A HREF="http://www.ctrl.org/">www.ctrl.org</A> DECLARATION & DISCLAIMER ========== CTRL is a discussion & informational exchange list. Proselytizing propagandic screeds are unwelcomed. Substance—not soap-boxing—please! These are sordid matters and 'conspiracy theory'—with its many half-truths, mis- directions and outright frauds—is used politically by different groups with major and minor effects spread throughout the spectrum of time and thought. That being said, CTRLgives no endorsement to the validity of posts, and always suggests to readers; be wary of what you read. CTRL gives no credence to Holocaust denial and nazi's need not apply. Let us please be civil and as always, Caveat Lector. ======================================================================== Archives Available at: http://peach.ease.lsoft.com/archives/ctrl.html <A HREF="http://peach.ease.lsoft.com/archives/ctrl.html">Archives of [EMAIL PROTECTED]</A> http:[EMAIL PROTECTED]/ <A HREF="http:[EMAIL PROTECTED]/">ctrl</A> ======================================================================== To subscribe to Conspiracy Theory Research List[CTRL] send email: SUBSCRIBE CTRL [to:] [EMAIL PROTECTED] To UNsubscribe to Conspiracy Theory Research List[CTRL] send email: SIGNOFF CTRL [to:] [EMAIL PROTECTED] Om
