DEE BREGER / SCIENCE PHOTO LIBRARY DEE BREGER / SCIENCE PHOTO LIBRARY
Wood structure. Coloured scanning electron micrograph (SEM) of wood from a Siberian pine tree (Pinus sibirica) from Mongolia. The vertical sections are growth rings, each representing one year's growth in the life of the tree. This wood dates from 534AD at far left to 539AD at far right. In the year 536AD the northern hemisphere experienced extreme cooling, which caused deformation of the wood's structure due to freezing of water within the cells. The following year, 537AD, was also cooler than average so less wood was laid down. Atmospheric cooling may have been caused by volcanism or a meteor impact. Magnification: x170 when printed 10cm high.
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