1. Geologic Time Scale (Earth is 4.6 billion years old)
The Earth’s Past
Geologic Time Scale
(Earth is 4.6 billion years old)

2. Geologic Time Scale
Time scale that outlines the development of Earth and of life on Earth
Time scale divisions based on major changes in the Earth’s surface, climate, or types of organisms
Time scale divisions usually based on dominant life forms

3. Geologic Time Units Eon Largest unit of time 4 eons Precambrian time
Hadean, Archean, Proterozoic, & Phanerozoic
Precambrian time
Hadean + Archean + Proterozoic
Covers about first 4 billion years of the Earth

4. Geologic Time Units (continued)
Eons broken into Eras
Phanerozoic  Paleozoic, Mesozoic, & Cenozoic
Eras broken into Periods
Periods broken into Epochs
Epochs can be broken into Ages

5. Geologic Units
Eons
Eras
Periods
Smaller
time units
Epochs
Ages

6. Eons and Eras

9. Geologic Columns
An ordered arrangement of rock layers that is based on the relative ages of the rocks in which the oldest rocks are at the bottom
Layers are distinguished by the type of rock and types of fossils in the rock

10. Grand Canyon Geologic Column

11. Grand Staircase RegionX X

13. X X X

14. Precambrian Time 4.6 Ga (Billion years) – 542 Ma (million years)
88% of Earth’s history
Little known about this time
Rocks are deformed and altered by tectonic activity

15. Precambrian Rocks & Life
Shields – large exposed Precambrian rocks
Nearly ½ of valuable mineral deposits found in shields
Life
Very few fossils
Stromatolites – blue-green algae deposits

16. Paleozoic Era
542 Ma – 251 Ma
Land masses started out apart but ended up together (Pangaea)
Rocks have lots of fossils
Plant & animal species increase dramatically at beginning of era
7 Periods

17. Cambrian Period Marine life forms
Warm shallow seas cover much of the continents
No evidence of land dwelling plants or animals

18. Ordovician Period Primitive fish Lots of invertebrates
First vertebrates (mostly fish) appear
No plant life on land

19. Silurian Period Vertebrate and invertebrate marine life dominate
Land plants & animals evolve near end of period

20. Devonian Period “Age of Fishes” Amphibians
Land plants and seed bearing plants evolve

21. Carboniferous Period Includes Mississippian and Pennsylvanian Periods
Climate was warm and humid
Forests and swamps responsible for coal deposits
Amphibians, fish, large insects

22. Permian Period Appalachian Mountains created
Shallow inland seas disappear
Mass extinction
Many invertebrates die out
Reptiles & amphibians survive

23. Mass Extinctions Used to indicate end of an era
Permian mass extinction
90% of marine organisms
70% of land organisms
Plenty of resources for other species to begin to dominate

24. Mesozoic Era 251 Ma – 65.5 Ma Pangaea breaks apart to form continents
Mountain ranges form
Sierra Nevadas, Andes
“Age of Reptiles”
Includes Triassic, Jurassic, & Cretaceous Periods

25. Triassic Period Dinosaurs – mostly 16 feet long Reptiles in the oceans
Ammonites – Mesozoic index fossil
First mammals appear

26. Jurassic Period Dinosaurs become dominant life form
2 major groups of dinosaurs
Saurischians – lizard hipped
Herbivores & Carnivores
Ornithischians – bird hipped
Herbivores
Flying reptiles
First birds

27. Cretaceous Period Dinosaurs still dominate T Rex
Horned and duck-billed dinosaurs
First flowering plants (angiosperms)
Magnolias, willows, oaks, maples, walnuts

28. Cretaceous-Tertiary Mass Extinction
C-T Extinction
End of Cretaceous Period
No dinosaur fossils found in rocks formed after Cretaceous Period
Due to environmental changes from continental movement or volcanic activity

29. C-T Extinction (continued)
Impact hypothesis
Giant meteorite crashed into the Earth
Produces dust that blocks the sun
Planet cools, plant life dies off, animals die off
Iridium near suspected impact site (Iridium is common in meteorites, but not Earth rocks

30. Cenozoic Era 65.5 Ma to present day
Continents move to present day position
Alps and Himalayas form
Ice ages
Mammals become dominant

31. Cenozoic Era (continued)
Divided into 2 periods
Tertiary Period
Time before the last Ice Age
Quaternary Period
From last ice age to present day
Divided into 7 epochs

32. Cenozoic Epochs Paleocene & Eocene Primates evolve
Whales, flying squirrels, bats
Still lots of small reptiles
Worldwide temp drops about 4oC at end of Eocene

33. Cenozoic Epochs (Continued)
Oligocene
Uplifting of Himalayas
World climate becomes much cooler & drier
Grasslands favored
Miocene
Antarctic ice caps begin to form
Mediterranean Sea fills and empties several times
Large land mammals
Earliest human ancestors(?)

34. Cenozoic Epochs (Continued)
Pliocene
Dramatic climate changes
Ice caps grow, water levels fall
Alaska and Russia connected by Bering land bridge
North and South America become connected
Species migrate into different continents

35. Cenozoic Epochs (Continued)
Pleistocene
Ice ages
Fossils of earliest modern humans
Holocene
11500 years ago as last ice age ends
Sea level rises 140 m
Great Lakes take their shape
Humans develop agriculture and begin to use tools