1. Geologic Time
Chapter 21.1, 22, 23, 24

2. Organization of Ch 21-24
Ch 21.1 – Describes the geologic time scale Ch 22 – Precambrian Earth Section 1: Early Earth Section 2: Formation of the Crust and Continents Section 3: Formation of the Atmosphere and Oceans Section 4: Early Life on Earth Ch 23 – Paleozoic Era Ch 24 – Mesozoic and Cenozoic Eras

3. Ch 21.1 Section Assessment Questions, pg 556: 1-7
How did geologists determine the divisions of the geologic time scale?
What does the geologic time scale indicate about the change in life-forms over time?
What do the names of the three eras of the Phanerozoic mean?
What major change occurred in life-forms at the end of the Proterozoic?
How were the geologic time periods named? On what basis are they defined?
Why is the use of living faunas acceptable for defining the periods and epochs of the Cenozoic Era?
Make bar graph showing breakdown of the scale.
Fossil record
Wide variety of life-forms, most have become extinct
Paleo – ancient, zoic – life, Meso – middle, Cenos – recent
Hard parts (skeletons, shells)
Location where rocks were first studied, distinctive groups that lived nearby, or a geographic feature , defined by the last fossil occurrence of a particular group of organisms
Many plans that originated during the Cenozoic era still exist today. Their fossils can be used to define the epochs of the Cenozoic.
Precambrian – 90%, Paleozoic – 6%, Mesozoic – 4%, Cenozoic – 1%

4. Why do we care?
By studying the characteristics of rocks and fossils within them, geologists can interpret
The environment the rocks were deposited in
Reconstruct Earth’s history
Possibly predict events or conditions of the future

5. Geologic Time Scale
Defn: record of Earth’s history from its origin to the present used by scientists around the world to correlate:
Geologic events
Environmental changes
Development of life-forms that are preserved in rocks
Names of periods don’t change, but the years marking the beg. and end are continually being refined.

7. Geologic Time Divisions
Eon – longest unit, measured in billions
Era – next-longest, hundreds of millions to billions
“Paleozoic” = old life
“Mesozoic” = middle life
“Cenozoic” = recent life
Period – 10’s to 100’s of millions of years
Epoch – smaller divisions, millions to 10’s of millions

8. Eons Longest unit Measured in billions Three Eons Archean Eon
(part 1 Precambrian Time)
NO LIFE
Proterozoic Eon
(part 2 Precambrian Time)
SINGLE-CELLED LIFE
Phanerozoic Eon
(3 Eras)
MULTICELLULAR LIFE

9. Eras Next-longest Hundreds of millions to billions
Defined by differences in life-forms found in rock
Three Eras
“Paleozoic” = old life
“Mesozoic” = middle life
“Cenozoic” = recent life

10. Periods Second shortest 10’s to 100’s of millions of years
Defined by life-forms that were abundant or became extinct during the time the rocks were deposited

11. Epochs Smaller divisions Millions to 10’s of millions
ONLY IN CENOZOIC…WHY?

12. Precambrian Time (Early Earth)
Makes up the first 90% of geologic time
Age of Earth
Land
Atmosphere
Oceans
Life

13. How old is Earth? 4.6 billion years old Evidence?
Rock age – 3.96 by (radiometric dating)
Zircon minerals – by (radiometric dating)
Meteorites – by (radiometric dating)
Moon rocks – 4.6 by (radiometric dating)

14. Land How did land form? Earth cooled and crust formed
Early crust used to be mainly basalt.
Densities of different materials sorted out the layers of earth (differentiation)
Melting of basaltic crust and then recrystallization formed granitic crust.
Why is the iron and nickel outer core liquid but inner core solid? More pressure in inner core increases its melting point. Less pressure in outer core.
Early Earth  molten rock Present  continents

15. Atmosphere Early Earth  Present Earth 
Carbon dioxide (CO2), N2, Methane (CH4), Water vapor (H2O), Carbon monoxide (CO), Ammonia (NH3)
HOT TEMPS
Present Earth 
N2 (71%), O2 (21%), Ar (0.9%), CO2
How?! Stromatolites!
Evidence?! Red beds!
Avg global temp is 25 degrees Celsius

16. Oceans Early Earth  NO OCEANS Present Earth  71% OCEANS! HOW?!
Meteorites and comets brought water
Volcanoes released during Archaean Eon (outgassing)
LOTS OF RAIN

17. Resources Climate Resource  http://www.scotese.com/climate.htm
Landmass Resource 

18. ERAS
Landforms
Flora (plants)
Fauna (animals)
Extinctions
Climate

19. Paleozoic Era - Landforms
- First supercontinent “Rodinia” had just broken apart - Plate tectonics, mountain building

20. Paleozoic Era - Flora
- Rainforests covered the earth - Vascular plants appeared (allowed for taller, stronger plants) - Ferns

21. Paleozoic Era - Fauna
- Reptiles appear - Amphibians - Fishes w/backbones (vert) - Trilobites (org w/hard parts) - Marine life!! - (Stromatolites in Precambrian)

22. Paleozoic Era - Extinctions
- End of Paleozoic Era was the Permian Extinction (more than 90% of species died) - 1st mass extinction ended the Ordovican period (marine life)

23. Paleozoic Era - Climate
- Global cooling continued - Ranged from temperate to cold to steamy swamp

24. Mesozoic Era - Landforms
- Breakup of “Pangaea” - Tectonic activity, mountain building - Sea levels rose

25. Mesozoic Era - Flora
- Flowering plants first evolved

26. Mesozoic Era - Fauna
- Birds evolve - Dinosaurs, Crocodiles, early mammals evolve, ocean/air reptiles evolve

27. Mesozoic Era - Extinctions
- Cretaceous extinction ended Mesozoic era and rid dinosaurs

28. Mesozoic Era - Climate
- Sandy, desert interior - Poles moist, temperate - Mild

29. Cenozoic Era - Landforms
- Major tectonic activity, continents moved to their current positions

30. Cenozoic Era - Flora
- Grasslands spread - Many more flowering plants

31. Cenozoic Era - Fauna
- Hominids, humans, cats, whales, bats

32. Cenozoic Era - Extinctions
- Due to changes in CO2, we could be entering the world’s next extinction? - Just like the extinction that killed the dinosaurs?

33. Cenozoic Era - Climate
- Most recent ice age - Climate changed back and forth, warmer and cooler