What makes wood petrify rather than decompose, and about how long does the process take?
Petrification is the process by which the small internal cavities of an organism are filled with mineral matter. With wood this can happen in a couple of ways. One way is for the dead trees to be knocked down and quickly buried. One common way for this to happen is to get caught in a volcanic ashflow. As water percolates through this ash, it dissolves various ions. These ions can then be precipitated into the cavities of the buried wood, thus petrifying it. The other way that this can happen is for the roots of the tree to be flooded with mineral rich water. As this water is drawn up into the tree the minerals precipitate out into the tissues killing the tree. These waters can be supplied by hot springs. Excellent examples of this process at work can be seen in some of the hot spring basins of Yellowstone National Park.
