FOSSILS Clues to Earths Past Creatures and Environment

FOSSILS Clues to Earth’s Past Creatures and Environment

SC Standard 8 -2. 2 Summarize how scientists study Earth’s past environment and diverse life forms by examining different types of fossils.

What is a fossil? • A fossil is the preserved remains or traces of an organism that lived in the past • Usually fossils are more than 10, 000 years old

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What do fossils tell us about Earth’s past? • Fossils are clues to: – The diversity of living things throughout Earth’s history – Past climate and surface changes – Changes that have occurred with organisms over time

Who studies fossils? • Paleontology is the study of fossils • Scientists who study fossils are called paleontologists

How are fossils classified? • Fossils are classified by how they are formed • Types of fossils: – – – Mold fossil Cast fossil Petrified fossil Preserved fossil Carbonized fossil Trace fossil

Mold Fossil • Forms when: – Sediments bury an organism – Sediments change into rock by pressure – The organism decays – Leaves a cavity or hollow in the shape of the organism

Cast Fossil • Forms when: – A mold is filled with sand or mud – Sediments harden into the shape of the organism

Mold and Cast Fossils • Most common form of fossils • Most fossils form when sediment buries a dead organism • Organism most likely lived in or near quiet water (swamp, lake, shallow sea)

Petrified Fossil • Also called permineralized fossil • Forms when: – Minerals from groundwater soak into the buried remains of organisms – Minerals replace the organic remains – Changes into rock

Preserved Fossil • Forms when: – Entire organisms or parts of organisms are prevented from decaying – Trapped in rock, ice, tar, or amber

Carbonized Fossils • Form when: – Organisms or parts are pressed between layers of soft mud or clay – Mud or clay hardens – Squeezes almost all the decaying organism away – Leaves the carbon imprint in the rock

Trace Fossils • Forms when: – Mud or sand hardens to stone where a footprint, trail, or burrow of an organism was left behind

Dino Tracks

The Fossil Record • Millions of fossils have been collected and studied from all over the world • Provides evidence of the history of life on Earth • Shows that different groups of organisms have changed over time http: //www. abc. net. au/beasts/fossilfun/burial/default. htm

Check for Understanding

Test Your Skills Which of the following is least likely to be found as a fossil? a. b. c. d. Clam shell Shark tooth Dinosaur bone Jellyfish imprint

Test Your Skills Fossils are usually found in _______? a. b. c. d. Desert land Mud Sedimentary rock Rocks formed inside volcanoes

Test Your Skills Fossils of animals found in the La Brea tar pits are examples of what kind of fossils? a. b. c. d. Carbon film Mold fossil Preserved remains Petrified fossil

Test Your Skills Marine fossils have been found in exposed rock layers in South Carolina. Which of the following is the best interpretation of this discovery? A. Marine organisms evolved from land-dwelling organisms. B. Parts of South Carolina were once covered by water. C. These organisms could live both in water and on land. D. They were carried by humans to South Carolina.

Test Your Skills Select the correct letter for the choices that are all definitely fossils. A. Egyptian Mummy, Ancient Pottery, Worm burrows in sandstone B. Imprints of rain drops, Trilobite shells, Mud cracks C. Dinosaur tracks, Mammoth found in ice, Seashells found in limestone D. Stone Age tools, Giant shark teeth, Seashells found on a beach

Test Your Skills Using the choices below, identify the fossils formed by petrification. A. Dinosaur tracks, Black outline of a plant leaf B. Rock-like wood, Rock-like Brachiopod shell C. Mud-filled shape of a gastropod shell, Mammoth droppings D. Insect in amber, Hollow cavity shaped like a trilobite

Do Now 1. What is sea-floor spreading? 2. How are mold and cast fossils related?