DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Petrified redwood (Sequoia affinis) longitudinal section, scanning electron micrograph (SEM). Petrified redwood showing lignified cell walls of the original xylem tissue still perfectly intact. Note the bordered pits in vertical vessel elements and also in the perpendicular ray cells. Petrifaction (petrification) is an important part of the fossil record. Petrified wood typically forms in sediment in the presence of mineral-rich water. Entire forests were petrified when volcanic eruptions occurred during the Eocene epoch (50 million years ago). Eruptions caused massive landslides and buried forests in layers of mud and ash. In the absence of oxygen, the wood was preserved. In wet areas, mineral rich water seeped into the wood cells and infused cell contents (lumens) with minerals (most often a silicate, such as quartz) to create a permanent record of the past. Magnification: x50 when shortest axis printed at 25 millimetres.
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