J OURNAL #26 Describe carbon dating and how it used to determine the numerical age of a rock layers.

The Fossil Record

L EARNING G OAL Today we will describe 4 ways in which entire organisms can be preserved as fossils and learn 5 examples of fossilized traces of organisms

T HE F OSSIL R ECORD Fossils- the remains of animals or plants that lived in a previous geologic time Paleontology- the study of fossils. Almost all fossils are discovered in sedimentary rock. The sediments that cover the fossils slow or stop the process of decay and protect the dead body from damage

T HE F OSSIL R ECORD The fossil record provides information about the geologic history of Earth. These dead organisms have changed throughout the geologic past and provide cluse to the environmental changes that occurred in Earth’s past. Example: marine animal fossils have been discovered in areas far from any ocean. This means that the area was previously covered by ocean in the past.

F OSSILIZATION Normally, dead plants and animals are eaten by other animals or decomposed by bacteria. If left unprotected, even the hard parts such as bones decay and leave no trace of the organism. Only dead organisms that buried quickly can become fossils. There are many ways fossils form.

H OW FOSSILS FORM : Mummification Amber (tree sap) Tar Seeps Freezing Petrification Imprints Molds and Casts Coprolites Gastroliths

T YPES OF F OSSILS Sometimes, no part of the original organism survives in fossil form. Trace fossils- a fossilized mark that formed in sedimentary rock by the movement of an animal on or within soft sediment. A trace fossil such as a footprint is an important clue to the animal’s appearance and activities.

T YPES OF F OSSILS Index fossils- a fossil that is used to establish the age of rock layers because it is distinct, abundant and widespread and existed for only a short span of geologic time. It must be present in rocks scattered over a large region It must have features that clearly distinguish it form other fossils. The organisms from which the fossil formed must have lived during a short span of geologic time. The fossil must occur in fairly large numbers within the rock layers.

L ET ’ S R EVIEW : What is a fossil? Name 4 ways in which an entire organism can be preserved as a fossil. The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock

L ET ’ S R EVIEW : What is paleontology? What are trace fossils? How do trace fossils help date sedimentary rock layers? The study of fossils A fossilized mark that formed by the movement of an animal on or within soft sediment. They occur only in rock layers of a particular geologic age