Earth Systems 3209

1. Earth Systems 3209 Reference: Chapters 6, 8; Appendix A & B Unit: 2Historical Geology

2. Unit 2: Topic3.2 Methods of Fossilization Focus on . . . • describe three conditions necessary for fossilization. • describe the formation of various types of fossils.

3. Conditions Necessary for Fossilization Rapid burial When an organism dies its soft parts are eaten by scavengers or isdecomposed by bacteria. However, if the organism is quickly buriedby sediment it is protected from the many environmental factors. • Presence of hard body parts • Fossils of organisms that contained hard parts are abundant in the fossil record, but only rare traces of soft tissue organisms are seen as fossils. Low oxygen environment In a low oxygen environment there is less bacteria and decomposition is slower, thus, organisms tend to have a greater chance to become fossilized when found in an oxygen poor environment.

4. 5 Methods of Fossilization Fossils are preserved in the rock record in several ways; 1) Petrifaction 2) Carbonization 3) Mold and Cast Text Reference: Pages 183-186 • Preservation • Ice, Mummification, and Amber • Traces • Tracks, Burrows, and Coprolites.

5. 5 Methods of Fossilization • 1) Petrifaction: • occurs when the small internalcavities and pores of the original structure are filled with precipitated mineral matter. • occurs when cell walls and solid material are removed and replaced by mineral material carried by underground water. • sometimes internal details and structuresare retained.

6. 5 Methods of Fossilization • 2) Carbonization: • occurs when fine sediment encloses delicate matter such as leaves in a oxygen poor environment. • As time passes, pressure squeezes out the liquid and gaseous components of the organism, leaving behind a thin residue of carbon.

7. 5 Methods of Fossilization • 3) Mold and Cast: • often preserve a replica of a plant or animal in sedimentary rocks. • an organism is buried in sediment and then dissolved by underground water leaving a hollow depression or an impression, called a mold. • The mold shows only the original shape and surface markings of the organism; it does not reveal the internal structure. • When minerals or sediment fills the hollow depression or impression it forms a cast.

8. 5 Methods of Fossilization • 4) Preservation: • Original remains can be preserved in ice or in amber (tree sap). • Both ice and amber protects theorganism from decay (oxygen free environment) and from pressures that would crush the organisms. • The entire animal has been preserved, even the soft parts which usually decay and disappear. Examples: Insects preserved in tree sap (amber). Cane in Jurassic Park.

9. 5 Methods of Fossilization • 5) Trace: • show traces left in the rock by an animal, such as; • Tracks - animal footprints made in soft sediment that later formed solid sedimentary rock. • Burrows- animal trails made in soft sediment that later formed solid sedimentary rock. • Coprolites - Fossil dung (feces) and stomach contents. • Gastroliths - Stomach stones.

10. Example 1: Which process would most likely preserve plant leaves? (A) carbonization (B) mold and cast (C) petrifaction (D) replacement What is the most common form of fossilization for wooly mammoths in northern Russia? (A) frozen remains (B) petrification (C) preserved in amber (D) preserved in tar pits

11. Example 2: Which statement is true regarding the Miocene worm trace fossil? (A) hard parts were preserved by petrification (B) no part of the worm has been preserved (C) soft parts were preserved by carbonization (D) the worm has been preserved in its original form

12. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Questions: A caribou dies and is laying on the edge of a river. Describe two conditions that favour the preservation of the remains of this specimen.

13. Solutions . . . Questions: A caribou dies and is laying on the edge of a river. Describe two conditions that favour the preservation of the remains of this specimen. Preservation of an organism is greatly increased when the following two conditions are met. The organism has hard body parts and is buried rapidly by sediment. Other conditions that promote the preservation of organisms is the absence of scavengers and microbes, and organisms are buried in an environment which is low in oxygen. If in a cold environment, the caribou could also be preserved (frozen) in snow and ice.

14. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Questions: • Fossils are commonly formed by the following methods: • formation of molds and casts • petrifaction by replacement • Describe these, including in your description, the conditions necessary for fossilization to occur.

15. Solutions . . . Questions: Fossils are commonly formed by the following methods:-- formation of molds and casts-- petrifaction by replacementDescribe these, including in your description, the conditions necessary for fossilization to occur.. Petrifaction:Hard parts of an organism, such as bone or trees, get buried rapidly in sediment. Pores and cavities in the material (organism) takes in water (fluid) which precipitates minerals to produce a solid replica of the organism, preserving all details, external and internal.

16. Solutions . . . Questions: Fossils are commonly formed by the following methods:-- formation of molds and casts-- petrifaction by replacementDescribe these, including in your description, the conditions necessary for fossilization to occur.. Molds and Casts:Organisms with hard parts get rapidly buried in sediment.The sediment compresses and hardens, the organism dissolves or decays, and an impression (mold) is left. For a cast to form, an impression (mold) fills with sediment or mineral matter which then hardens forming a solid representation ofthe organism.Only external features are fossilized.

17. Summary . . . Overview of Points covered: • Conditions for fossilization: 1) Rapid burial 2) Hard Body Parts 3) OxygenlessEnvironment • 5 Methods of Fossilizations: 1) Petrifaction 2) Carbonization 3) Mold and Cast 4) Preservation 5) Trace Fossils