SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY
Fossilised bones. Bones (dark areas) of an unidentified dinosaur preserved in a rock. The head of a hammer gives approximate scale. Fossils are formed when animal remains are buried under sediment, which excludes oxygen and bacteria, preventing decay. The bones are also protected from weathering processes. Over millions of years the bones undergo mineralization, becoming hard rock. Photographed in Portugal.
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