Paleontologists study how fossils become preserved. The chance that an organism will be preserved as a fossil is low. When an organism dies, its body decays and the skeleton falls apart. The soft tissues, such as the skins of animals or the leaves of plants, are usually destroyed. They break down into simpler chemical compounds. Hard body parts, such as bones, are much more likely to be preserved. However, they often become separated and broken into pieces. Geological processes such as erosion, weathering, and sedimentation, constantly destroy fossils before anyone sees them.