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Fossils Fossil – Remains of prehistoric life used to match rocks of similar age in different regions Conditions Favoring Preservation: Hard parts and rapid burial!!!!! How Do Fossils Form? Usually organism dies and is covered with mud or sediment (The key is that it has to be in an anaerobic environment – anaerobic means there is no ? _______________) The organism then slowly decays and leaves either a hole in the shape of its body or has minerals fill in the hole. Fossil Types: 1. Petrified – cavities and pores filled with precipitated mineral matter ex. Wood Fossil Types Cont: 2. Replacement –Cell material is replaced with mineral material - If the minerals are carried in groundwater, the fossil is called permineralized Trilobite – living tissue replaced with calcite (Found in Washtenaw – Devonian age 360 – 408 mya) This is a permineralized cross-section of part of a tree trunk. Because water carried the minerals that replaced the tissue, sometimes little bits of the original tissue gets preserved and we can get DNA from it (like in Jurassic Park!) 3. Mold –Hard part is buried then dissolved by underground water – only imprint is left Tree Mold – formed as lava flowed around a tree. Moisture in tree kept it from burning up for long enough for lava to cool around it (Found at Craters of the Moon Nat'l Park) 4. Cast –Hollow space of mold is filled with mineral matter ex. Fossil shell Internal Cast of a Brachiopod Silurian Age, 438 to 408 mya 5. Carbonization –Remains covered by fine sediment; pressure from above squeezes out liquids & gases and leaves carbon residue ex. Some ferns (will look black) Carbonized Fern 6. Impression –Replica of fossil’s surface (a carbonized fossil that loses carbon residue) An impression and the same type of leaf found now 7. Amber –Petrified wood resin that may have trapped plants or animals Spider caught in Amber 8. Indirect evidence- including tracks, burrows, coprolites (fossilized dung) Coprolite (dino dung) Dino Tracks Principle of Fossil Succession: Fossils follow each other in a definite order & any time period can be identified by its fossils (Esp. it index fossils – common prevalent fossil of time period) i.e. Simple shelled organisms followed by trilobites Fossil Succession – Fossils organisms change in dominance in a definite pattern Name that fossil type! Name that fossil type! Name that fossil type! More Pompeii Pics