Electron microscopic characterization of cell wall degradation of the 400,000-year-old wooden Schöningen spears

Abstract

The cell wall degradation of 400,000-year-old wooden spears, excavated in 1994 at the Schöningen brown-coal opencast mine (100 km east of Hannover/Germany), was examined by transmission electron microscopy. The degradation of the spears was confined to surface layers only, inner parts remained without structural changes. Features in some of the wooden portions, such as a greater lignification of the outer part of the S2 layer and the absence of intercellular cavities suggested that the samples also contained mild compression wood. The presence of both normal and compression wood provided an opportunity to compare the extent of cell wall degradation in these two types of wood. The normal wood cell walls were more severely eroded than the walls of compression wood tracheids. Cell wall erosion in the normal wood extended to the middle lamella in places. The observations indicated an attack of cell walls by erosion bacteria only. As the spears had been buried underground, these observations are consistent with the emerging knowledge that normally erosion bacteria are responsible for the deterioration of buried and wet archaeological woods because they are more tolerant to extremely low oxygen levels. © Springer-Verlag 2005.