What Is a Fossil?

1) A mold fossil is typically the detail left after an organism decays. 2) A trace fossil is the record of an organism's activity. 3) A petrified fossil is when a living thing is turned to rock. 4) An external mold fossil is a hollow form. 5) An internal mold fossil is a solid copy. Evidence: 1) According to the National Park Service, "Mold fossils form when sediments fill the spaces left by the organism and then harden. The hardened material makes a cast or mold of the organism, which can be used to create a relief or three-dimensional copy of the organism." 2) A study published in the journal Palaios states that "trace fossils are the physical record of an organism's activity, rather than the organism itself." 3) According to National Geographic, petrified fossils are created when "a tree or other organic material is buried quickly by sediment, cutting it off from the oxygen in the air that would normally cause it to decay." This causes the organic material to be replaced by minerals, which turn it into rock. 4) According to the Paleontological Research Institution, external mold fossils are "shaped like the organism they represent, but they are hollow and thin, and usually no more than a few millimeters thick.” 5) According to the Paleontological Research Institution, internal mold fossils are a "solid inner cast of the organism."