1. Geologic Time

2. Geologic Time Scale
Divisions of Earth’s history based on life forms that were living during certain periods

3. Separation = Change.
Correlate geologic events, environmental changes, and changes among life forms

4. The Geologic Time Scale
Record of Earth’s history
Names of the time periods don’t change but their boundaries are always being changed.

5. Scale is cut into different sections:
Eon – longest time unit on the scale
Hadean (oldest)
Archean
Proterozoic
Phanerozoic (youngest)

7. Era – next longest span of time
Defined by the different life forms that are found in the rocks. Marked by major, striking, worldwide changes like mass extinction
Precambrian (oldest)
Paleozoic
Mesozoic
Cenozoic (youngest)

9. Precambrian Era – microscopic life
Paleozoic Era – Age of Trilobites
Mesozoic Era – Age of Reptiles
Cenozoic Era – Age of Mammals

10. Periods – defined by the life forms that were abundant or became extinct during the time in which the rock was deposited. Third longest division of time.

12. Epochs – smaller division of geologic time.

13. Trilobites
Make excellent index fossils b/c their characteristics changed every period
Paleontologists uses changes to determine the environment

14. Movement of Pangea Closed seas Formed mountains
Not a completely acceptable explanation for extinctions

15. Precambrian Time 4.5 billion yrs – 544 million yrs
Longest part of Earth’s history
Little known about org. in this time period b/c:
4 million yr old rock buried deeply and experiences enough heat & pressure to destroy fossils
Most org. had soft parts

16. Precambrian Time How life changed:
Cyanobacteria – algae that photosynthesized producing O2
O2 created ozone layer allowing the evolution of more complex organisms
Invertebrates – (no backbone) appeared towards end of Precambrian Time
Ex: jellyfish, worms

17. Precambrian Time End: Extinctions New org. out-competed old org.
Scientists not completely sure

18. Paleozoic Era – Era of Ancient Life
544 million yrs – 248 million yrs
How life changed:
mostly marine org. so large seas
Trilobites and shelled org. common so abundance of fossils

19. Paleozoic Era Vertebrates (backbone) evolved
Forest appeared – gymnosperms – plants producing seeds only
Vertebrates began to adapt to land = amphibians ex. Frog
Purpose was org. needed to survive in oxygen poor waters
Can’t keep moisture in their bodies and need water to lay their eggs

20. Paleozoic Era
Several mtn. building episodes – Appalachian Mountains formed
End:
90% of marine, 70% land species died
Volcanoes?
Asteroid/comet collision?

21. Mesozoic Era – Middle Life
248 million yrs – 65 million yrs
How life changed:
Pangea seperated into 2 landmasses Laurasia, Gondwanaland
Reptiles
Dinosaurs

22. Mesozoic Era Birds appeared during Jurassic Period
Mammals appeared during Triassic Period
Angiosperms – flowering plants – started evolving during Cretaceous Period

23. Mesozoic Era End: Mass extinction
Comet/asteroid collision causing dust/smoke to block out sun
Some survivors

24. Cenozoic Era – Recent Life
65 million yrs – present
How life changed:
Mountain building episode: Alps, Andes, Himalayas
Grassland expansion – grazing mammals become larger

25. Cenozoic Era
Continents split further, org. became isolated and began to evolve
Marsupials – koala, wombat, kangeroos
HUMANS