Fossils are the preserved evidence of plants or animals. For such remains to be considered fossils, scientists have agreed that they must be over 10,000 years old. There are two main types of fossils: body fossils and trace fossils. Body fossils are the preserved physical remains of an actual plant or animal. Trace fossils are the remains of the activity of the animal, such as preserved impressions, footprints, fossilized egg shells, or nests.