Chapter 9: Earth s Past

Chapter 9: Earth s Past

Vocabulary 1. Geologic column 2. Era 3. Period 4. Epoch 5. Evolution 6. Precambrian time 7. Paleozoic era 8. Shield 9. Stromatolite 10. Invertebrate 11. Trilobite 12. Index fossil 13. Brachiopod 14. Graptolites 15. Vertebrates 16. Eurypterids 17. Carboniferou s 18. Mass extinction 19. Mesozoic Era 20. Creataceous- Tertiary mass extinction 21. Cenozoic Era 22. Holocene Epoch

I. Divisions of Geologic Time A. The geologic history of Earth is marked by major changes in Earth s surface, climate, and types of organisms. 1. Geologists use these indicators to divide the geologic time scale into smaller units. 2. Rocks grouped within each unit contain similar fossils and each unit is generally characterized by fossils of a dominant life-form.

B. Eons 1. Largest unit of geologic time 2. Four eons within Earth s history 3. The first three eons are collectively known as Precambrian time a. This 4 billion year interval contains most of Earth s history. C. Eras: subdivisions of eons D. Periods: subdivisions of eras; characterized by specific fossils & named for locations where fossils are found

E. Epochs 1. Subdivisions of periods 2. Periods are divided into epochs when there is more complete fossil evidence 3. Epochs are divided into ages, which are defined by the occurrence of distinct fossils

II. Precambrian Time & the Paleozoic Era A. Scientists agree that Earth formed about 4.6 billion years ago; the time period from the formation to 542 million years ago is known as the Precambrian 1. Rocks & fossils from this time are difficult to interpret since it s been altered by tectonic processes 2. Shields: large areas of exposed Precambrian rock

3. Precambrian rock rarely includes fossils likely lacked bone to fossilize 4. Most common fossil is cyanobacteria a. Contained in stromatolites: layered reef-like deposits that form in warm, shallow waters b. Stromatolites indicate that most of the Earth was covered in shallow seas during this time c. Other Precambrian fossils include marine worms, jellyfish, and single-celled organisms

B. Paleozoic Era 1. Divided into 6 periods: 2. Cambrian period (542 Ma 488 Ma): sponges, snails, clams and worms evolve 3. Ordovician period (488 Ma 444 Ma): first fishes evolved and other species become extinct

4. Silurian period (444 Ma 416 Ma): land plants, insects and spiders appear 5. Devonian period (416 Ma 359 Ma): amphibians evolve, cone-bearing plants start to appear 6. Carboniferous period (359 Ma 299 Ma): Tropical forests appear, reptiles evolve 7. Permian period (299 Ma 251 Ma): Seed plants become common, insects and reptiles become widespread; sea animals and some amphibians begin to disappear; Pangaea fully formed

III. Mesozoic Era A. The Age of Reptiles! B. Divided into 3 periods: 1. Triassic period (251 Ma 200 Ma): turtles and crocodiles evolve and dinosaurs appear; first small mammals appear 2. Jurassic period (200 Ma 146 Ma): large dinosaurs roam the world. First mammals and birds appear 3. Cretaceous period (146 Ma 65.5 Ma): dinosaurs dominate, flowering plants appear, trees appear (maple, oak, walnut)

C. Land changes 1. Pangaea began to split as tectonic plates drifted and collided produced Sierra Nevada & Andes mountains 2. Shallow seas with some desert areas 3. Warm and humid

D. Cretaceous-Tertiary Mass Extinction (65.5 Ma) 1. Also called K-T Extinction 2. No dinosaurs are found in fossils more recently than the Cretaceous Period 3. Leading theory is impact hypothesis asteroid crashed into Earth & produced large amounts of dust & debris in the atmosphere, blocking the sun for many years. Temperatures dropped, many plants became extinct, and so did the animals that relied on them

IV. Cenozoic Era A. The Age of Mammals B. Divided into 2 periods: 1. Tertiary period (65.5 Ma 1.8 Ma) a. Paleocene & Eocene Epochs (65.5 Ma 33.9 Ma): small rodents, early horses, whale, & primates evolved; temperature dropped about 4 C b. Oligocene & Miocene Epochs (33.9 Ma 5.3 Ma): Indian & Eurasian subcontinents collided, creating the Himalayas; climate became cooler & drier; early deer, pigs, camels, cats, wolves/dogs, etc.

c. Pliocene Epoch (5.3 Ma 1.8 Ma): first modern horses, predators, herbivores; climate began to change & ice sheets began to spread; land bridges formed between North & South America and Eurasia & North America 2. Quaternary period: humans evolve and large mammals like woolly mammoths become extinct. a. Pleistocene Epoch (1.8 Ma 0.0115Ma): ICE AGE; earliest Homo sapiens b. Holocene Epoch (11,500 years ago now): glacial period ended; current coastlines emerged; Great Lakes formed

TIMELINE! Label ALL eras, periods, and epochs First minerals (4.2 bya) First rock (3.6 bya) Unicellular life appears (3.5 bya) Multicellular life appears (2.5 bya) Cambrian Explosion (430 Ma) Land plants appear (400 Ma) Vertebrates appear (380 Ma) First amphibians (370 Ma) First reptiles (320 Ma) Permian mass extinction (251 Ma) First modern birds (160 Ma) K-T mass extinction (65.5 Ma) First hominids (0.3 Ma = 300,000 years) Modern Ice Age begins (0.02 Ma = 20,000 years) Modern humans! (0.0115 Ma = 11,500 yrs) Recorded history (0.006 Ma = 6,000 yrs)