CHAPTER 4 Geologic Time

Review: What do fossils show about past environments? past life?

Review: How does the law of superposition relate to rock layers? What is the oldest rock layer? Which rock layer is an intrusion? Which rock layer is younger C or E?

Review: Why are index fossils important?

Finding Clues to Rock Layers

ANSWERS: Finding Clues…. SITE 1 What “fossil clues” in layers A and B indicate the kind of environment that existed when these rock layers were formed? SHELLS AND FISH WOULD INDICATE A WATER (AQUATIC) ENVIROMENT How did the environment change in layer D? FOOT PRINTS WOULD SIGNIFIY A CHANGE FROM WATER TO LAND Which layer is the oldest? __A___ How do you know? BECAUSE IT IS AT THE BOTTOM

ANSWERS: Finding Clues…. SITE 1 Which of the layers formed most recently? ___G___ How do you know? BECAUSE IT IS ON THE TOP Why are there no fossils in layers C and E? BOTH ARE EXTRUSIONS – COOLED LAVA What kind of fossils occurred in layer F? TRACE FOSSILS Using your knowledge of geologic time, what major event most likely happened when layer C was formed? VOLCANIC ERUPTIONS AND EXTINCTIONS

ANSWERS: Finding Clues…. SITE 2 8. Which layer at Site 1 might have formed at the same time as layer W at Site 2? B 9. Which is older, intrusion V or layer Y? ___LAYER Y__ How do you know? INTRUSIONS ARE YOUNGER THAN THE ROCK AROUND THEM 10. Which rock layers are missing? A, D, AND 1 EXTRUSION 11. If the absolute age of the intrusive layer is radioactive dated to be about 150 million years ago, what would you be able to infer about the age of the extrusive layer? EXTRUSIVE LAYER IS OLDER THAN 150MYA

CHAPTER 4 LESSON 4 and 6 GEOLOGIC TIME SCALE

GEOLOGIC TIME SCALE is the record of the geologic events and the evolution of life forms. Divisions of geologic time are used to date events in Earth’s History. PRECAMBRIAN Time: Beginning of Earth’s History (88% of history) and ended 542 mya. Very few fossils survived but stromalites are most common. ERAS: Three long units of time between now and Precambrian time. PERIODS: Each era is divided periods (smaller segments of time).

PALEOZOIC ERA (542-251 mya) Lots of changes from the sea to the land Invertebrates: Trilobites (huge arthropods), Brachiopods (clam like), Jellyfish, Sponges, Giant insects (land) Vertebrates: Fish, Amphibians, and First Reptiles Plants: Simple Land Plants, Ferns, and Cone Bearing Trees Permian Mass EXTINCTION: 90% ocean life died, 70% land life died

MESOZOIC ERA (251-66 mya) Age of the Reptiles Fish, insects, reptiles, and cone-bearing plants survived the extinction Triassic: Dinosaurs appeared 225mya and small mammals first appeared Jurassic: Dinosaurs common on land, reptiles lived in ocean and air, and first birds appeared (Archaeopteryx) Cretaceous: Birds started replacing reptiles in the air, flying reptiles become extinct, first flowering plants and fruits. Cretaceous MASS Extinction 65mya: more than ½ of all plants and animals died, including all dinosaurs

CENOZOIC ERA (66mya – Current) Age of the Mammals Paleogene/Neogene: Climate was warm and mild, Mammals evolved – whales, dolphins, and large land mammals (grazers and carnivores), Grasses became widespread Quaternary: Climate cooled and warmed causing several ice ages, Glaciers covered Europe and North America, Mammals such as bats, cats, dogs, cattle, Woolly Mammoths and Rhinos, Humans appeared