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Looking at Fossils – Ch 9 Section 1

Looking at Fossils – Ch 9 Section 1. Fossilized Organisms. Fossils are the remains or trace of an organism that lived long ago; mostly preserved in sedimentary rock. They can form several ways. 5 ways are: In rocks In amber (sap) In ice In asphalt (tar pits) By petrification.

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Looking at Fossils – Ch 9 Section 1

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  1. Looking at Fossils – Ch 9 Section 1

  2. Fossilized Organisms • Fossils are the remains or trace of an organism that lived long ago; mostly preserved in sedimentary rock. • They can form several ways. 5 ways are: • In rocks • In amber (sap) • In ice • In asphalt (tar pits) • By petrification

  3. Fossilized Organisms In rocks: buried by sediment, slowing decay. Hard parts (shells, bones, teeth) resist decay; fossils form as sediment hardens In amber: caught in tree sap and sap hardens (good samples) In ice: frozen remains preserved (also good samples – more tissues) In asphalt: stuck in asphalt (tar pits) By petrification: buried in sediment; minerals replace tissue.

  4. Trace Fossils Are fossilized structures, such as a footprint, that formed in sedimentary rock from animal activity on/within soft sediment Trace fossils are evidence of activity. Examples are fossilized footprints, burrows, and coprolite (dung) Footprints and burrows fossilize when sediment fills them in and then hardens. Coprolite is petrified dung

  5. Trace Fossils “Talk” Fossilized footprints can tell us about animal’s size, speed, and even habits such as whether they lived alone or in herds. Fossilized burrows can tell about how animals got shelter. Coprolite can tell about an animal’s diet and health

  6. Mold and Cast Fossils A mold is an imprint of where a dead animal or plant originally was left in sediment. A cast is the hardened sediment that filled a mold. Both a cast or a mold can show what an organism looked like on the inside or outside.

  7. Science Tool Scientists compare fossils to learn about similarities between them and to learn about the extinct organisms. Scientists compare fossils with current living species to see how life has changed. Fossils are evidence. However, only a few organisms eventually become fossils.

  8. Fossil Record • Is the history of life in the geologic past based on the trace or remains of organisms. • Fossil records provide evidence about the past.

  9. Fossil Record as Evidence Fossil Record provide evidence about organisms and…..GeologyMarine (sea life) fossils found in mountains means that those mountains were once underwater. ClimateFossil evidence of forests and freshwater organisms in Antarctica indicate climate change – that the region used to be much warmer.

  10. Incomplete Fossil Record • The fossil record is incomplete because:1) Not all organisms become fossils (only a fraction do): a) More likely for organisms with hard parts (bones, teeth, shells) to fossilize than those with just soft tissue. b) Even with hard parts, the environment needs to be suitable for fossilization. 2) Not all fossils have been found

  11. Dating the Fossil Record • Absolute dating (testing for “exact” age) can be done on some fossils. • Relative dating (determining if older or younger than another fossil or rock layer) the MOST COMMON method; superposition theory most commonly used.

  12. Index Fossils • Are fossils that can be used to determine the age of a rock layer because the fossil is extinct, abundant (plenty), species short-lived, and fossil is widespread (all over world); it must also be easy to identify

  13. Trilobites – an Index Fossil • Phacops (a kind of trilobite) • Determined to live ~400 million years ago. • Scientists know if a phacop fossil is found, the rock layer is ~400 million years old.

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