The primary wall, which may be relatively thick, consists mostly of cellulose and hemicellulose, in contrast to the thinner secondary wall that is largely composed of a mixture of cellulose and lignin. Wood cell walls consist of an outer primary wall that encloses a multilayered secondary wall. Lignin and cellulose, the primary constituents of wood, may undergo alteration on a microscopic level, even though the overall appearance of the ancient wood may appear unchanged. Environments that favor mummification include deeply submerged wood, burial in impermeable sediments, aridity, or low temperatures. This preservation is a result of several factors: inhibition of wood-destroying microbes, decreased oxygen availability, and the absence of harsh chemical or physical conditions (e.g., high alkalinity or acidity, or elevated temperatures). Mummified wood consists of original tissues that have undergone minimal degradation of cellular constituents. The most important conditions required for mummification are an absence of microbial and chemical degradation, and burial conditions where mineral-bearing groundwater is unable to penetrate the tissues. In siliceous hot springs, wood may become rapidly impregnated with silica, but in other environments, buried wood may be preserved for tens of millions of years without experiencing mineralization. Less well-known are fossil forests where ancient trees have been preserved as original tissue, or as organic material that has undergone structural alteration.Ī common question asked of fossil wood researchers is “how long does it take for wood to become petrified?” There is no uniform answer, because fossilization processes are highly variable. Recent reports describe these mineralization processes in detail, and list earlier literature. The infiltration and replacement of inorganic minerals produces petrified wood that has sufficient durability to be preserved for many millions of years. The ages of these living trees are brief in comparison to fossil evidence of trees that comprised ancient forests. the 80,000 year age estimated for ~47,000 component trees of a Quaking Aspen ( Populus tremuloides) grove in central Utah, USA. The ages of clonal tree clusters, where individual trunks share a common root network, may be much greater, e.g. The oldest known age record for an individual tree is a Bristlecone Pine ( Pinus longaeva) growing in White Mountains of California USA a tree core taken in 2012 was observed to have 5067 annual rings. Foresters describe forests that contain trees with ages of only a few hundred years as “old growth”. These factors determine whether a region is an arid desert or a lush rainforest. From a deep time perspective, forests are a transient phenomenon, their existence depending on environmental factors that include elevation change, atmospheric physics, ocean currents patterns, and tectonic plate motion.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |