SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY
Welwitschia (Welwitschia mirabilis) growing in a petrified forest. This succulent plant is a living fossil, meaning that it is a species known to exist currently and to exist in fossil records. It has only two leaves and can live for in excess of 1000 years. Petrifaction is the process by which the tree's organic matter has been replaced with minerals which preserve the original structure of tree. It is a subterranean process in which sediments are first laid down on the tree after which water flows through the sediments. Over time the tree's cells are replaced with minerals from the water which form stone in their place. Photographed in Namibia.
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