The Rock and Fossil Record IV. Looking at Fossils

A. Fossilized Organisms 1. Fossils a.the remains or physical evidence of an organism preserved by geologic processes b.most often preserved in sedimentary rock 2. Fossils in Rocks a.when organisms die, they decay or are consumed by other animals b.sometimes they are buried in sediment, which slows decay c.hard parts of organism are more commonly preserved in the rock 3. Fossils in Amber a.Hardened tree sap is called amber b.Insects get caught in tree sap, which then hardens c.Frogs and lizards have also been found in amber

4. Petrifaction a. the process in which minerals replace an organism’s tissue b. permineralization 1. process in which the pore space in an organism’s hard tissue is filled with mineral c. replacement 1. process in which the organism’s tissues are completely replaced by minerals.

–5. Fossils in Asphalt a. asphalt bubbles up to the surface in thick, sticky pools b. animals get trapped in the material and preserved c. La Brea tar pits in California –6. Frozen Fossils a. cold temperature slow the decay of animals b. animals from the last ice age have been found c. 20,000 year-old woolly mammoth has been found in Siberia

B. Other types of Fossils 1. Trace Fossils –a. any naturally preserved evidence of animal activity –b. fossils form when animal footprints fill with sediment and get preserved in rock –c. tracks reveal how big and fast the animal was and if it traveled in a herd –d. burrows, shelters made by animals, is another trace fossil –e. coprolite is fossilized animal dung 2. Molds and Casts –a. a cavity in rock where a plant or animal was buried is called a mold –b. a cast is an object created when sediment fills a mold and becomes rock

C. Using Fossils to Interpret the Past 1. The information in the Fossil Record –a. fossil record is only a rough sketch –b. some parts are more complete than others –c. scientists know more about animals that lived in areas that were more favorable to fossil formation –d. most organisms never became fossils –e. many fossils have never been discovered

2. History of Environmental Changes –a. marine fossils help scientists reconstruct ancient coastlines and deepening and shallowing of ancient seas –b. using fossils of plants and animals, scientists can reconstruct past climates –c. they can tell how different the climates are from today 3. History of Changing Organisms –a. studying the relationships between fossils, scientists can interpret how life has changed –b. older rock layers contain organisms that are often different from the organisms found in younger rock layers –c. scientists compare those organisms to try to fill in the blank spots in the fossil record

D. Using Fossils to Date Rocks –1. index fossils are fossils that are found in the rock layers of only one geologic age and that is used to establish the age of rock layers –2. ammonites a. one type of index fossil b. tropites were a marine mollusk similar to a modern squid that lived between 230 and 208 mya c. when found, it tells that the rock is 230 to 208 million years old –3. trilobites a. fossils of phacops are an index fossil b. lived 400 mya c. when found, it tells that the rock is 400 million years old