Carbon 14 not used for dating dinosaur
Some fossils consist only of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. In some cases the original remains of the organism completely dissolve or are otherwise destroyed.The remaining organism-shaped hole in the rock is called an external mold.The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host.
Often, however, the phytoleim is lost and all that remains is an impression of the organism in the rock—an impression fossil.In this case the fossil consists of original material, albeit in a geochemically altered state.This chemical change is an expression of diagenesis.If this hole is later filled with other minerals, it is a cast.An endocast or internal mold is formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail or the hollow of a skull. If the chemistry is right, the organism (or fragment of organism) can act as a nucleus for the precipitation of minerals such as siderite, resulting in a nodule forming around it.