Essentials of Geology, 9e

1. Essentials of Geology, 9e Earth History: A Brief Summary Chapter 19

2. Early evolution of Earth • Origin of planet Earth • Most researchers believe that Earth and the other planets formed at essentially the same time from the same primordial material as the Sun • Nebular hypothesis • Solar system evolved from an enormous rotating cloud called the solar nebula • Nebula was composed mostly of hydrogen and helium

3. Early evolution of Earth • Origin of planet Earth • Nebular hypothesis • About 5 billion years ago the nebula began to contract • Assumes a flat, disk shape with the protosun (pre-Sun) at the center • Inner planets begin to form from metallic and rocky clumps of substances with high melting points • Larger outer planets began forming from fragments with a high percentage of ices - water, carbon dioxide, methane and ammonia

4. Early evolution of Earth • Formation of Earth’s layered structure • As Earth formed, high-velocity impacts caused the temperature to increase and iron and nickel began to melt and sink toward the center • Buoyant masses of molten rock rose to the surface to produce a primitive crust

5. Early evolution of Earth • Formation of Earth’s layered structure • Early chemical segregation established the three basis divisions of Earth’s interior • an iron-rich core • a thin, primitive crust • the mantle between the core and crust • A primitive atmosphere evolved as gaseous materials escaped from Earth’s interior

6. Earth’s atmosphere evolves • Primitive atmosphere formed from volcanic gases • A process called outgassing • Water vapor, carbon dioxide, nitrogen, and several trace gases • Very little free oxygen • Water vapor condenses and forms primitive oceans as Earth cools

7. Earth’s atmosphere evolves • Bacteria evolve • Plants evolve and photosynthesis produces oxygen • Oxygen content in the atmosphere increases • By about 4 billion years after Earth formed, abundant ocean-dwelling organisms that require oxygen existed

8. Earth’s history • Precambrian era • 4.5 billion to 540 million years ago • 88% of Earth's history • Only sketchy knowledge • Most Precambrian rocks are devoid of fossils

9. Earth’s history • Precambrian era • Precambrian rocks • Most are buried from view • Each continent has a "core area" of Precambrian rocks called a shield • Extensive iron ore deposits • Absent are fossil fuels

10. Precambrian shields Figure 19.3

11. Earth’s history • Precambrian era • Precambrian fossils • Most common are stromatolites • Material deposited by algae • Common about 2 billion years ago • Microfossils of bacteria and algae have been found in chert • Southern Africa (3.1 billion years of age) • Lake Superior area (1.7 billion years of age)

12. Earth’s history • Precambrian era • Precambrian fossils • Plant fossils date from the middle Precambrian • Animal fossils date from the late Precambrian • Diverse and multicelled organisms exist by the close of the Precambrian

13. The geologic time scale Figure 19.2

14. Earth’s history • Paleozoic era • 540 million years ago to about 248 million years ago • First life forms with hard parts • Abundant Paleozoic fossils • Early Paleozoic history • Southern continent of Gondwanaland exists

15. Earth’s history • Paleozoic era • Early Paleozoic history • North America • A barren lowland • Seas move inland and recede several times and shallow marine basins evaporate leaving rock salt and gypsum deposits • Taconic orogeny, a mountain building event, affects eastern North America

16. Reconstruction of Earth in early Paleozoic time Figure 19.9 B

17. Earth’s history • Paleozoic era • Early Paleozoic life • Restricted to seas • Vertebrates had not yet evolved • Life consisted of several invertebrate groups • Trilobites • Brachiopods • Cephalopods • First organisms with hard parts, such as shells - perhaps for protection

18. A natural cast of a trilobite Figure 19.7 A

19. Earth’s history • Paleozoic era • Late Paleozoic history • Supercontinent of Pangaea forms • Several mountain belts formed during the movements of the continents • World's climate becomes very seasonal, causing the dramatic extinction of many species

20. Formation of Pangaea in late Paleozoic time Figure 19.9 D

21. Earth’s history • Paleozoic era • Late Paleozoic life • Organisms diversified dramatically • Land plants • Fishes evolve into two groups of bony fish • Lung fish • Lobe-finned fish which become the amphibians

22. Earth’s history • Paleozoic era • Late Paleozoic life • Insects invade the land • Amphibians diversify rapidly • Extensive coal swamps develop

23. Earth’s history • Mesozoic era • 248 million years ago to about 65 million years ago • Often called the "age of dinosaurs" • Mesozoic history • Begins with much of the world's land above sea level • Seas invade western North America

24. Earth’s history • Mesozoic era • Mesozoic history • Breakup of Pangaea begins forming the Atlantic ocean • North American plate began to override the Pacific plate • Mountains of western North America began forming

25. Reconstruction of Earth in the late Jurassic period Figure 19.13 B

26. Earth’s history • Mesozoic era • Mesozoic life • Survivors of the great Paleozoic extinction • Gymnosperms become the dominant trees • Reptiles (first true terrestrial animals) readily adapt to the dry Mesozoic climate • Reptiles have shell-covered eggs that can be laid on the land

27. Major reptile groups in the Mesozoic era Figure 19.14

28. Earth’s history • Mesozoic era • Mesozoic life • Dinosaurs dominate • One group of reptiles led to the birds • Many reptile groups, along with many other animal groups, become extinct at the close of the Mesozoic • One hypothesis is that a large asteroid or comet struck Earth • Another possibility is extensive volcanism

29. The Chicxulub impact site Figure 19 B

30. Earth’s history • Cenozoic era • 65 million years ago to the present • Often called the "age of mammals" • Smaller fraction of geologic time than either the Paleozoic or the Mesozoic • North America • Most of the continent was above sea level throughout the Cenozoic era

31. Earth’s history • Cenozoic era • North America • Many events of mountain building, volcanism, and earthquakes in the West • Eastern North America • Stable with abundant marine sedimentation • Eroded Appalachians were raised by isostatic adjustments

32. Earth’s history • Cenozoic era • North America • Western North America • Building of the Rocky Mountains was coming to an end • Large region is uplifted – Basin and Range province is formed, Rockies are re-elevated, rivers erode the Grand and Black canyons, and volcanic activity is abundant

33. Earth’s history • Cenozoic era • Cenozoic life • Mammals replace reptiles as the dominant land animals • Angiosperms (flowering plants with covered seeds) dominate the plant world • Strongly influenced the evolution of both birds and mammals • Food source for both birds and mammals

34. Earth’s history • Cenozoic era • Cenozoic life • Two groups of mammals evolve after the reptilian extinctions at the close of the Mesozoic • Marsupials • Placentals

35. Earth’s history • Cenozoic era • Cenozoic life • Mammals diversify quite rapidly and some groups become very large • e.g., Hornless rhinoceros, which stood nearly 16 feet high • Many large animals became extinct • Humans evolve

36. End of Chapter 19