Geologic Time Scale

1. Geologic Time Scale Earth Science Spring 2014

2. The Geologic Column • Geologic column- arrangement of rock layers based on the ages of the rocks • No single area on earth a record of all geologic time • Observations from around the world were used to create the geologic column • Represents a timeline of the earth’s history • Rock layers are distinguished from one another primarily by the fossils they contain and the type of rock they are made of

3. Divisions of Geologic Time • Earth’s history is divided by: • Major surface or climate changes • Extinction of various species • **these types of events are used to divide the geologic time scale into smaller units

4. Divisions of Geologic Time • Eras • Era- largest unit of geologic time • 4 geologic eras • Precambrian • Paleozoic • Mesozoic • Cenozoic

5. Divisions of Geologic Time • Eras • Precambrian Era (Precambrian Time) • Earliest era • Oldest layer of the geologic column • Longest era (4 billion years) • Very few fossils • Makes it difficult to divide into smaller units • Bacteria, algae, primitive worms, sponges, & corals • Evidence that life started in the ocean

6. Divisions of Geologic Time • Eras • Paleozoic Era • 2nd era • Means “ancient life” • 292 million years long • Fossils- wide variety of both marine & land plants & animals

7. Divisions of Geologic Time • Eras • Mesozoic Era • 3rd era • Means “Middle Life” • 183 million years long • Fossils- more complex organisms like reptiles & birds

8. Divisions of Geologic Time • Eras • Cenozoic Era • Present geologic era • Means “recent life” • Fossil- mammals are common

9. Divisions of Geologic Time • Periods- subdivision of a geologic era • Characterized by specific fossils • Named for the location in which the fossils were first found • Epochs – subdivision of a geologic time period • Contain an extremely detailed fossil record • 2 period of the cenozoic era are divided into these

10. Geologic History • Theory of evolution • Theory that organisms change over time and that new organisms are derived from ancestral types. • First proposed by Charles Darwin by way of natural selection (survival of the fittest) • Evidence: • Fossil record • Examination of living organisms

11. Geologic History • Theory of Evolution cont… • Geologic changes & climatic changes affect the survival of organisms • Example of geologic change is a dramatic decrease in the amount of the earth’s surface covered by water • Example climatic change is a decrease in atmospheric temperature

12. Geologic History • Precambrian Time • Makes up 88% of the earth’s history • Began with the formation of the earth 4.6 billion years ago & ended 540 million years ago • Rocks from this era are difficult to interpret • Shields of precambrian rock are found on every continent • Fossils are rare • Most common are stromatolites

13. Stromatolites

14. Geologic History • Paleozoic Era • Began 540 million years ago & ended about 248 million years ago • It is believed that Pangea formed by the end of this era • Abundant fossil record • Rich in marine & land animal & plant fossils • Divided into 7 periods

15. Geologic History • Paleozoic Era- Cambrian Period • Contains the first advanced marine life • Most of the continents were covered with warm, shallow oceans. • Marine invertebrates thrived here • Invertebrates- animals without backbones • Most common- trilobites • Brachiopods- shelled animals • 2nd most common type of animal to live during this time • Still no evidence of land-dwelling plants or animals

16. Geologic History • Cambrian Period

17. Geologic History • Paleozoic Era- Ordovician Period • Number brachiopod species increased & number of trilobites decreased • Large number of coral started to appear • Graptolite- useful index fossil • First vertebrate appeared • Vertebrate- animal with a backbone • Still no plant life on land

18. Geologic History • Ordovician Period

19. Geologic History • Paleozoic Era- Silurian Period • Marine life continued to thrive & evolve during this time. • Echinoderms became more numerous • Eurypterids- scorpion-like sea creatures were abundant • Near the end, land plants & animals started showing up • Ex: spiders, millipedes

20. Geologic History • Silurian Period

21. Geologic History • Paleozoic Era- Devonian Period • Many kinds of bony fish • Lungfish- air breathing fish • Rhipidistians- land going fish • 1st true amphibian showed up • Ichthyostega- like a huge salamander • Land plants began to develop • Giant horsetails, ferns, cone-bearing plants.

22. Geologic History • Devonian Period

23. Geologic History • Paleozoic Era- Carboniferous Period (Pennsylvanian & Mississippian) • Climate was generally warm & the humidity was high all over the world • Forests & swamps covered much of the land • Amphibians & fish continued to thrive • Crinoids were common in oceans • Insects were common on land • Reptiles appeared & resembled large lizards • Many of the coal, oil, & natural gas deposits are found in rocks from this period

24. Geologic History • Carboniferous Period

25. Geologic History • Paleozoic Era- Permian Period • End of the Paleozoic Era • Mass extinction of many Paleozoic life forms • Nearly all continents had joined to form Pangea • Areas of desert & savannah formed in the interior of the continent • Shallow seas evaporated • Many species of marine invertebrates became extinct

26. Geologic History • Mesozoic Era • Began 248 million years ago • Ended 65 million years ago • Pangeabroke up into the continents • Tectonic plates drifted & collided forming mountain ranges • Shallow seas & marshes covered most of the land • Climate was warm & humid. • Favored reptiles

27. Geologic History • Mesozoic Era- Triassic Period • Dinosaurs first appeared • Dinosaurs varied greatly in size • Lush forests of cone-bearing trees & cycads • New forms of marine life appear • Earliest mammals made their appearance

28. Geologic History • Mesozoic Era- Jurassic Period • Dinosaurs were the dominant form of life • 2 major groups of dinosaurs evolved. • Saurischians- both carnivores & herbivores • Ornithischians- herbivores • Flying reptiles were common

29. Geologic History • Mesozoic Era- Cretaceous Period • Dinosaurs continued to dominate the earth • Tyrannosaurus rex • Ankylosaurs-armored bodies • Ceratopsians- horned • Ornithopods- duck-billed • 1st flowering plants appeared (angiosperms) • End of this period was marked by a mass extinction

30. Geologic History • Cenozoic Era (Age of the Mammals) • Began 65 million years ago • Continents in the beginning looked much like they do today • Increased tectonic activity • Dramatic climate changes • Mammals became the dominant life form

31. Geologic History • Cenozoic Era (Age of the Mammals) • 2 periods • Tertiary • Time before the last ice age • Quaternary • Began with the last ice age & includes present time • ** divided into 7 epochs • Tertiary- Paleocene, Eocene, Oligocene, Miocene, & Pliocene • Quaternary- Pleistocene & Holocene

32. Geologic History • Cenozoic Era: Paleocene & Eocene Epochs (Tertiary Period) • Paleocene Epoch • Many new mammals evolved • Small rodents • 1st primates appeared • Eocene Epoch • First flying squirrels, bats, and whales appeared • Smaller reptiles flourished • World wide temperature dropped 4 degreed Celsius

33. Geologic History • Cenozoic Era: Oligocene & Miocene Epochs (Tertiary Period) • Oligocene Epoch • Climate continued to become cooler & drier • Early mammals became extinct • Larger species of today’s common animals flourished • Himalaya mountains formed • Miocene Epoch • Climate still dry & cool • Golden Age of Mammals • Common fossils include: deer, rhinoceros, & pig families • Largest known mammals lived • Modern polar ice caps started to form

34. Geologic History • Cenozoic Era: Pliocene Epoch (Tertiary Period) • Hunting animals became fully evolved • Fossils of first modern horses • Great climatic changes occurred & continental ice sheets began to spread • Land bridge between Eurasia & North America appeared • North & South America became connected by the central American Land Bridge

35. Geologic History • Cenozoic Era: Pleistocene & Holocene Epochs (Quaternary Period) • Pleistocene Epoch • Several periods of glaciation occurred over most of North America & Eurasia • Many animals became extinct • Fossils of early ancestors of humans • Holocene Epoch • Began about 11,000 years ago as the last ice age ended • Sea level rose drastically as glaciers & ice sheets melted • Great Lakes were formed • Modern humans developed • Agriculture developed • Use of bronze & iron tools began