DO NOW Turn in Review #3 Pick up notes and Review #4.

REVIEW What era: Was the age of fish? Did humans appear? Did flowers appear? Did dinosaurs go extinct? Did Pangaea form? Did the greatest extinction occur? You need to know the answers to all these questions for your unit test!

Index Fossils and Geologic Time SES4. Students will understand how rock relationships and fossils are used to reconstruct the Earth’s past. SES4e. Use stratigraphic relationships to interpret major events in Earth history.

SPECIAL FOSSILS Every fossil tells us something about the age of the rock it's found in. Some fossils that tell us more because they are found exclusively in rock layers of a specific geologic age. Called INDEX FOSSILS.

CHARACTERISTICS OF INDEX FOSSILS Abundant - distributed over a wide area. Common - large numbers within a rock layer. Distinctive - easy to recognize. Limited – from a short, specific geologic time span.

MORE ON INDEX FOSSILS Index fossils are used to establish the relative and absolute ages of the rock layers in which the fossils are found Finding a specific index fossil, you know the absolute age of the rock. Based on its position, you now the relative age of the rock.

MORE ON INDEX FOSSILS Used to date rock layers found in widely separated areas – can help determine age of sedimentary rock. In order for an organism to be used as an index fossil, the organism must have been geographically widespread and must have existed for a geologically short time and deposited over a large area!

INDEX FOSSILS: TRILOBITE Paleozoic Era – Cambrian to Permian Extinction Most diverse group of extinct animals preserved in the fossil record.

INDEX FOSSILS: TRILOBITE Fairly large and hard-bodied. More than 20,000 Individual species appeared and went extinct at the end of the Paleozoic era - allows for more precise geologic dating.

INDEX FOSSILS: TRILOBITE Paleozoic: Different species, different periods

INDEX FOSSILS: AMMONITES Appeared late Paleozoic – Common during Mesozoic period. Extinction with dinosaurs at end of Mesozoic. Predatory, squid-like creatures that lived inside coil-shaped shells.

INDEX FOSSILS: AMMONITES Sharp, beaklike jaws inside a ring of tentacles that extended from their shells to snare prey, Range of sizes - Some more than three feet across in size.

INDEX FOSSILS: AMMONITES Suture patterns more complex over time – used for dating as index fossil

OTHER INDEX FOSSILS

REVIEW Index fossils are useful for dating sedimentary rocks because: they are abundant, distinctive, and unlimited they are limited, distinctive, and uncommon they are uncommon, abundant, and distinctive they are abundant, common, and distinctive

TO DO Work on Fossil lab Work on Geologic Timeline Review #3 due Monday