Petrified trees. Fossilised remains of trees in the Petrified Forest National Park,Arizona,USA. Tall,pine-like trees covered parts of the flood plain that occupied this area in the late Triassic period (225 million years ago). Fallen trees were washed by swollen streams & covered in silt,mud & volcanic ash,which excluded oxygen & slowed their decay. In time,water containing silica minerals seeped through the logs & encased their woody structures in silica. This slow process evolved with the silica crystallising into quartz,and the logs were preserved as petrified wood. Geological uplifting & the more recent effects of wind & water have exposed the logs to the surface | |
Licence : | Droits gérés |
Crédit: | Science Photo Library / Fraser, Simon |
Taille de l’image : | 4905 px × 3648 px |
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