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Politics : Formerly About Advanced Micro Devices -- Ignore unavailable to you. Want to Upgrade?

To: J_F_Shepard who wrote (825523)	12/25/2014 10:07:28 AM
From: Brumar89	1 Recommendation Recommended By FJB Read Replies (1) \| Respond to of 1578901

I guess you just have a problem with science: Carbon starvation in glacial trees recovered from the La Brea tar pits, southern California Pertenece a: PubMed Central (PMC) PubMed Central (PMC3 - NLM DTD) Descripción: The Rancho La Brea tar pit fossil collection includes Juniperus (C3) wood specimens that 14C date between 7.7 and 55 thousand years (kyr) B.P., providing a constrained record of plant response for southern California during the last glacial period. Atmospheric CO2 concentration ([CO2]) ranged between 180 and 220 ppm during glacial periods, rose to ?280 ppm before the industrial period, and is currently approaching 380 ppmin the modern atmosphere. Here we report on ?13C of Juniperus wood cellulose, and show that glacial and modern trees were operating at similar leaf-intercellular [CO2](ci)/atmospheric [CO2](ca) values. As a result, glacial trees were operating at ci values much closer to the CO2-compensation point for C3 photosynthesis than modern trees, indicating that glacial trees were undergoing carbon starvation. In addition, we modeled relative humidity by using ?18O of cellulose from the same Juniperus specimens and found that glacial humidity was ?10% higher than that in modern times, indicating that differences in vapor-pressure deficits did not impose additional constrictions on ci/ca in the past. By scaling ancient ci values to plant growth by using modern relationships, we found evidence that C3 primary productivity was greatly diminished in southern California during the last glacial period. http://biblioteca.universia.net/html_bura/ficha/params/title/carbon-starvation-in-glacial-trees-recovered-from-the-brea-tar/id/912067.html I don't know why you have a problem. Atmospheric CO2 levels were very low during the last ice and plants need CO2 to live, grow and thrive. When it gets low enough, growth is stunted and plants suffer from not enough CO2. Trees preserved in the tar pits showed that was happening then. Now how did atmospheric CO2 levels get so low? Because nature has been removing carbon from the atmosphere for millions of years, locking it up in fossil fuels and other things like calcium carbonate (limestone).