"When the preservation is right, petrified wood can tell of ecological and climatological conditions of an environment long ago." "Much like the study of growth rings in modern wood, petrified wood can be very useful in learning about the growing conditions a tree experienced in the ancient past," Sunderlin said. So, what about petrified wood's scientific value? Can studying it provide any valuable insights? "We have petrified wood in the fossil record in these and other paleoenvironmental settings ever since the Devonian Period, more than 350 million years ago," Sunderlin said. Once the wood was buried in these locations, groundwater supplied the sediments needed to petrify the wood and eventually remove all of the tree's original organic matter. These are areas that were once ancient floodplains or lake systems where low dissolved oxygen levels prevented microbial decay. "Many of the world's most famous petrified wood localities are in exposed sedimentary rocks that were deposited in fluvial-lacustrine paleoenvironmental conditions," Sunderlin said. Those long timescales mean petrified wood forms better in some environments and locations than in others. The exact amount of time needed for wood to become petrified depends on the conditions - the main one being how rich the groundwater is in minerals such as silica - but generally ranges from hundreds of thousands of years to millions of years.
Much of the petrified wood we see in the rock record, though, formed over longer timescales of thousands to millions of years and, sometimes, re-mineralization in multiple stages." These accumulate substantial mineral deposits in their woody tissues year after year. "There are some incipient petrified wood pieces being formed in fallen logs in mineral hot springs, such as those at Yellowstone National Park. " can take a very long time on a human time-scale, but sometimes we see cases of amazingly quick wood preservation by these mineralization processes," Sunderlin said. "The former process is called permineralization, while the latter is simply called replacement." How long does it take for wood to become petrified? "The mineralization can be from either - or, much more often, both - mineral precipitation in or between the wood's cellular structures, or mineral replacement of the actual organic material that once made up the cell walls of the wood," Sunderlin said. So, although the material is called petrified "wood," it is actually not wood at all rather, the minerals have replaced and taken on the appearance of the wood that was once there.
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