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This article discusses the formation of fossils, including various methods such as molds, casts, refrigeration, encasement, and petrification. It also explains the concept of index fossils, pattern of faunal succession, and the evidence for evolution found in the fossil record.
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Thursday, February 10th, 2011 • Tasks • Take out Tully Monster Article • Turn in E.C. • Objectives • Understand how fossils were formed • Homework • LTs due tomorrow • Q.O.D. • What is a fossil?
Fossils • Any part, remnant or evidence left by an organism in a rock • Fossils are found in sedimentary rocks
How Fossils are Formed • Original Remains • Actual unchanged remains • Wooly Mammoths • Replaced Remains • Hard parts have been replaced by minerals • Petrified wood
How Fossils are Formed • 5 ways • Molds • Casts • Refrigeration • Encasement • Petrification
How Fossils are Formed • Mold • Creature is dissolved completely out of the rock leaving a depression • Cast • New material fills the mold
How Fossils are Formed • Refrigeration • Freezing organism • Preserved in ice • Wooly Mammoth in glaciers
How Fossils are Formed • Encasement • Organism is enclosed by material that prevents decay • Example • Ants in amber • Tar pits
How Fossils are Formed • Petrification or permineralization • Mineral crystals replace cells in the organism • Example • Petrified wood
Trace Fossil • Evidence of life other than the remains of a plant or animal • Footprints • Tracks • Burrows • Borings
Index Fossil • Fossils that are typical of a particular time segment of Earth’s history.
3 Characteristics of Index Fossils • 1.) Must be easily recognizable. Unique in some way so they can easily be told from other similar fossils. • 2) Must be widespread in occurrence. Geographically. • 3.) Limited in time.
Key Bed • A single rock layer that has the same characteristics as an index fossil. • Example – A large volcanic eruption.
Evidence for Evolution • Pattern of Faunal Succession -the oldest rocks contain no fossils, first fossils appear simple, new rocks contain complex organisms
Charles Darwin • Studied the fossil record and living organisms; developed an explanation for the appearance of new species -New species evolve from existing forms by process of Natural Selection -those organisms which are best adapted to their environment will survive and have the most offspring, which will inherit adaptations
when fossils are arranged according to their age in sedimentary rocks, they show progressive changes and different groups of organisms coexist at different times. Principle of Fossil Succesion
Hiatus – location where the rock record is missing one or more layers
K-T Boundary • The divisions of the time scale were based on the observations that large percentages of animals and plants became extinct at certain intervals. The most talked about of these is the extinction at the end of the Cretaceous (KT extinction) .
Fossil Evidence • Direct • Actual organism is preserved in some way • Indirect • A replica or model of the organism shape or an activity it made
Which ones are direct? • Refrigeration • Encasement
Which ones are indirect? • Molds • Casts • Petrification
