1. Diff Geo Unit 2
Chapters 21, 22, 23, and 24

2. CHAPTER 21

3. Geologic Time
Geologists use the rock record to see what happened during earth’s past
Time is divided up into units starting at 4.6 billion years ago to today
The bottom of the geologic time scale is the oldest
Eons, eras, periods, epochs
Eons- longest
Epochs- shortest

4. Eras we need to know Precambrian (oldest and longest) Paleozoic
Mesozoic
Cenozoic
Don’t worry about the periods or epochs

5. Relative Dating
Relative dating allows scientists to have an idea of how old rocks are, in comparison to others
They use principles and laws to guide them

6. Principle of Uniformatarianism
Processes that are taking place today in the natural environment were also happening long ago
Erosion
Earthquakes
Volcano eruptions
Etc.

7. Law of original horizontality
Sedimentary rocks left undisturbed will be deposited in layers

8. Law of superposition
In an undisturbed sequence of rock, the oldest layers will be at the bottom and younger rocks as you travel upward toward the surface

9. Law of cross-cutting relationships
An intrusion or fault must be younger than the rock it cuts through
The cheese has to be there before you can cut it 

10. Unconformities A break in the rock record
Disconformities- sed over sed rock (da same kind of rock)
Nonconformity- sed over non-sed rock (not da same kind of rock)
Angular unconformity- layers are at an angle and have been eroded

11. Correlation
Using similar rock outcrops from different areas means they are similar ages
Usually contain index fossils
Organisms that lived for a small time over a wide geographic range

12. Absolute dating Radioactive dating
Using radioactive isotopes whose half lives are known to calculate the exact age of the rock
Half life- time it takes for half the element to decay
Organic uses Carbon-14
Inorganic uses Uranium and other elements

13. Radioactive Decay Problem
A rock contains 0.75 of lead-206 for every g of uranium-238. The half-life decay for uranium to turn into lead is 45,000 yrs. How old is the rock?
Hint: Start by figuring out the amount of Uranium remaining.

14. Dendrochronology- counting annual growth rings in trees to get exact age
Seasonal changes causes an alternation in sediment deposits called varves.

15. Types of fossils Original preservation
All the soft and hard parts remain

16. Altered hard parts
Minerals replace hard parts
Soft parts are gone

17. Molds
Outline of what once lived
Casts
Filled in mold
3D model

18. CHAPTER 22 PAGES ONLY

19. Precambrian era
Zircon found from meteorites that impacted early earth are used to date the planet
It is a radioactive element

20. Earth’s heat sources Radioactive decay in the core
Previous impact from asteroids and meteorites
Gravitational contraction

21. Earth’s layers differentiated based on density
Densest went to the core
Lightest to the crust
Formed the plates, which have moved throughout time due to convection currents in the mantle

22. The Precambrian atmosphere
Initially lots of hydrogen and helium
With continual out gassing of volcanoes increased water vapor, carbon dioxide, and nitrogen emitted
Cooling of air caused the water vapor to condense, form clouds, and precipitate
This filled the oceans

23. Oxygen was emitted by uni-cellular cyanobacteria that underwent photosynthesis to create their own food
Fossilized mats of cyanobacteria called stromatolites are evidence
Iron-banded formations containing iron oxide called red beds also are evidence

24. Later in the Precambrian
During the Proterozoic
Unicellular (prokaryotes) began to engulf each other
Gave rise to multi-cellular (eukaryotes)
Previously soft bodied organisms
Difficult to preserve

25. CHAPTER 23

26. Paleozoic Era
Continents moving from the original land masses to different arrangements
Changes in sea level
Evidence of this shown in transgressions and regressions in the rock record
Produced most likely by glaciations

27. Transgression
Sea level rises
Shore moves inland
Regression
Sea level falls
Shore moves out seaward

28. Early Paleozoic life found in Burgess Shale
Small, wild looking sea creatures
Middle Paleozoic saw the rise of vascular plants which allowed nutrients to flow through stems and leaves
Between the middle and late Paleozoic, there was a mass extinction of marine life due to global cooling

29. Mountain building occurred
Large plates combined in different ways
Coal deposits formed in swampy areas
Coral reefs formed

30. In Late Paleozoic
Sharks and ray finned fish
Lobe finned fish like lungfish
Ferns and seed bearing plants on land
Amphibians in coal swamps
Reptiles evolved amniotic egg which allowed them to live farther from water
Mass extinction due to loss of seas

31. CHAPTER 24

32. Mesozoic Era
Pangaea broke up and formed the Atlantic Ocean as well as the Mid-Atlantic Ridge
Mountains formed in North America
North America developed arid climates
Universal warmer climate

33. Mesozoic known as the age of reptiles (ecotherms- cold blooded)
Also first small mammals, birds, and flowering plants
Phytoplankton in the oceans creates oxygen during photosynthesis
Ammonites are index fossils of this time
Angiosperms are seed bearing plants with flowers

34. Small mammals were endotherms (warm blooded)
Lots of large dinosaurs
Even flying dinosaurs!

35. Saurischia
Lizard hipped dinosaurs
Plant eaters and meat eaters
Brontosaurus
Tyrannosaurus Rex
Ornithischia
Bird hipped dinosaurs
Plant eaters
Stegosaurs
Ankylosaurs

36. Mass extinction at the end of the Mesozoic Era
We think it was a huge meteorite that crashed into the (now) Gulf of Mexico
Evidence
Iridium found in the layer of clay that was deposited around this time period
Radiometrically dated to 65 million years ago

37. Cenozoic Era Climate change caused by position of the continents
Change in ocean circulation caused ice ages
Mountain building occurred

38. Cenozoic era is the age of mammals
Small and later larger mammals
Saber tooth cats
Wooly mammoths
Primates
Humans

39. Hominoid
Larger group including the hominids
Includes great apes
Hominid
Bipedal
Walk upright
Homo sapiens