The document discusses geologic time and how rocks are dated. It describes how radiometric dating is used to determine the absolute age of rocks by measuring radioactive decay. The oldest rocks on Earth are around 3.96 billion years old. It also discusses the theory of uniformitarianism and how the same geologic processes that shape the Earth today have operated throughout its history.

1. The Lithosphere
Chapter 9

2. Geologic Time
• Human time is mere seconds when
compared to the time frame over which
geologic processes have been operating to
develop landforms

3. Geologic Time

4. How do we date rocks?
Relative time
• Superpostion
Oldest rocks on the bottom, youngest rocks on the
top
Absolute time
• Radiometric dating
Atoms with unstable nuclei (isotopes) decay into
stable forms
Each isotope has a specific decay rate
Half-life--the length of time it takes one half the isotope to
decay
Measuring the ratio of unstable to stable material

5. The oldest rocks
Earth first condensed and formed into a planet
about 4.6 billion years ago.
Oldest rocks are from the Acasta Gneiss in
northwestern Canada: 3.96 billion years old
Oldest grains of rock, from Western Australia: bet.
4.2 and 4.4 billion years old
5

6. Uniformitarianism
Uniformitarianism
“The present is the key to the past.”
In other words: The same physical processes active
in the environment today have been operating
throughout geologic time.

7. Earth’s Interior Structure

8. Earth’s magnetic field
• Circulations within Earth’s inner and outer
cores may be the mechanism for the
magnetic field, called the magnetosphere,
that protects Earth from solar wind and
cosmic radiation.
• The magnetic north and south poles migrate
• Geomagnetic reversal also happens in
irregular intervals
8

9. From the crust on down

10. Which elements make up
Earth’s crust?
• Core
–Fe, Ni, Si (and/or) O
• Mantle
–O, Si, Mg, Fe, Ca, Al
• 99% of the crust is made up of 8 elements:
–O, Si (make up 74.3%)
–Al, Fe, Ca, Na, K, Mg
10
These elements, and trace others, combine to
make up Earth’s minerals and rocks...

11. What is a Mineral?
A mineral is…
a naturally-occurring,
homogeneous solid
with a definite
(but generally not fixed)
chemical composition
and a highly-ordered
atomic arrangement.
It is usually formed through
inorganic processes.

12. Okay…quick quiz…
Does ice fit the definition of a mineral?

13. ...naturally-occurring...
Diamonds

14. ...homogeneous solid...
It can’t start out as one mineral and become
another mineral halfway through (but it can change
color and still be the same mineral)
Tourmaline (Elbaite variety):
Na(Li1.5,Al1.5)Al6Si6O18(BO3)3(OH)4

15. ...definite (but generally not fixed)
chemical composition...
Quartz
SiO2 (silicon dioxide)
Olivine
(Mg, Fe)2SiO4

16. ...highly-ordered atomic
arrangement.
• Carbon dioxide gas is made up of atoms that
are not all bonded together into a structure.
• When frozen, CO2 IS bonded together...
forming...what?

17. The shape of the mineral crystal is the result of
its internal atomic structure.
chains
flat sheets
cubes
rhombohedrons
asbestos (crocidolite)
muscovite mica
galena
rhodochrosite

18. What if a substance doesn’t fit the
whole definition?
It’s a mineraloid.
Some substances look like minerals--but they LIE.
Glass is a mineraloid. It has an “amorphous” atomic
structure.
- O
- Si

19. As light passes through the glass panels, it is distorted by
the ripples in the glass. Which panel is the new one?

20. Biogenic minerals: Exceptions to
the “inorganic processes” rule
Formed by living things
The pearl and shells of oysters
• Aragonite
The main mineral found in human
bones and teeth
• Apatite

21. Biogenic minerals: Exceptions to
the “inorganic processes” rule
Formed by living things
Diatoms and radiolarians in the
ocean
• Silicate minerals
• Their skeletons are used as polishing
agents...
...(in your toothpaste!)

22. Is coal a mineral?

23. Is coal a mineral?
No.
Coal, petroleum, and peat are NOT minerals.
–They have no definite chemical composition
–They have no ordered atomic arrangement
Petroleum, coal and peat are mineraloids

24. Is coal a mineral?
But…coal, peat, and petroleum can form minerals
under certain conditions
For example: If coal beds are heated to high temperatures and
the carbon in them is crystallized, they can form the mineral,
graphite

25. Mineral Formation:
Non-organic formation
Minerals can form from:
–Magma
–Steam (these minerals are called vaporites)
–Mineral components left behind when water
evaporates (these are called evaporites)
–Mineral components dissolved in water that solidify
again (these are called precipitates)

26. From cooled magma
The mineral components come together in the
melt and harden as molten rock material
solidifies

27. From steam: vaporites
Vaporite
–Water near a magma source heats up, dissolves
mineral components in surrounding rocks, and
carries them away
–The steam condenses at the surface. The mineral
compounds also “condense” and solidify.
Commonly found around volcanic
vents, these sulfur crystals are
forming around Kilauea Crater, Hawaii.
Also found near oceanic volcanic
vents (at spreading centers).
Harvesting sulfur crystals from a volcano in Indonesia

28. From steam: vaporites
Harvesting sulfur crystals from a volcano in Indonesia

29. From evaporating water: evaporites
Evaporite
–Water evaporates, but leaves behind any mineral
compounds that were dissolved in the water
–Hint: “Please pass the halite!”
Salt crystals like these form in
salt beds along the edge of
Highway 84, just before the
Dumbarton Bridge.

30. Precipitate
–When in too high a concentration to remain
dissolved in a liquid, the mineral components
condense and may actually “rain” (precipitate)
out of solution
–Often occurs when warmer water, which can
hold more dissolved solids, cools slightly
Mineral Formation:
Non-organic formation

31. From dissolved solids: precipitates
Oolitic beach sand from the Caribbean, the Bahamas,
and Great Salt Lake in Utah form from calcium carbonate
precipitating out of the water

32. From dissolved solids: precipitates
Pyrite “sand dollars” form in sea water and collect on the
ocean floor

33. Experiment
Make a precipitate mineral at home...

34. What is a Rock?
• A solid, cohesive aggregate of one or
more minerals or mineral materials
–A few rock varieties are made up almost
entirely of one mineral—this is called a
pegmatite
• Example: massive accumulations of halite

35. The Rock Cycle
Rocks have been continuously forming and
reforming over millions and millions of years
The rock cycle is a closed flow system

36. The Rock Cycle

37. What is the power source that
drives the rock cycle?
• Earth’s internal heat
–Radioactive decay from its initial formation
• the power source for the flow system
• The sun
–Secondary power source
–Drives weather systems that erode material

38. Convection Currents
• Slow-moving convection
currents within the mantle
transfer heat from the outer
core to the upper mantle
• The convergence and
divergence of these currents
near the surface is believed to
be one of the driving forces
behind the movement of
Earth’s crustal plates

39. The 3 Classes of Rock
Classified based on the processes which form
them
Igneous rocks
Sedimentary rocks
Metamorphic rocks

40. Igneous Rocks
from cooling magmas
• The kinds of rocks you end up with (and
ultimately the kinds of structures built by the
formation of those rocks) are determined by the
chemistry of the magmas you start with

41. Felsic Magmas
• The “fel” is for feldspar (made from Si, Al, O), “si” is for
silicates (made from Si and O)
• Lighter in color, lower in density than mafic minerals
• Continental crust is predominantly felsic material

42. Felsic Magmas
• Cooler magmas, containing lots of silica (SiO2)
• Highly viscous (resistant to flow)
• High concentration of gases under high pressure
• Gases can’t rise easily, so they stay trapped until near
the surface
• As pressure is released at the surface, these
pressurized gases tend to explode
– (Example: Mount St. Helens)

43. Mount Saint Helens
• The explosion blew off 1,300 feet of the mountain's top and
sent ash and debris more than 12 miles into the sky
covering three states - Washington, Oregon, and Idaho.
Sixty two people were dead, beautiful forests and lakes
were destroyed resulting in $3 billion worth of damage.
• ‘[At about 10:00 a.m.] in the city of Yakima, Washington…a
black cloud covered the city and "snowed" ash. [Not] a
street light nor a neighbor's porch light could be seen. The
ash was so heavy it sank swimming pool covers and caved
in old roofs. Businesses and schools were closed down
and all normal activity… ceased to exist.”
From Disasters: Blowing Your Top
http://www.boisestate.edu/history/ncasner/hy210/volcano.htm

44. Felsic Magmas
Explosive Mount St. Helens
(Pre-eruption)

45. Felsic Magmas
Explosive Mount St. Helens
(May 18, 1980)

46. Felsic Magmas
Explosive Mount St. Helens
Mt. St. Helens Today

47. • The “ma” is for magnesium, the “f” for iron (Fe--
ferris); contains more metallic, heavy elements
(Al, Mg, Fe, K, Ca)
• Darker in color, higher in density
• Oceanic crust is predominantly mafic
• Low viscosity (flow easily for long distances)
• Very little gas content, relatively little SiO2
• Hotter magmas, so gasses stay dissolved
• Rarely explosive
– (Example: Hawaiian volcanoes)
Mafic Minerals and Rocks

48. Mafic Magmas
Hawaii
2002-10-11 view northwest across coastal plain of Kilauea from West
Highcastle lava delta to Pu`u `O`o in upper right skyline

49. Intrusive vs. Extrusive
Igneous Rocks
• Intrusive igneous rocks—magma cools
beneath the crust; crystals have more time to
form; harder, more erosion-resistant rocks
• Extrusive igneous rocks—magma cools on
the surface (lava); crystals don’t have time to
form good crystal faces, if it cools fast
enough, no crystals will form (obsidian--
“volcanic glass”)

50. Extrusive Igneous Rocks
Basalt and Obsidian

51. Intrusive Igneous Rock
Granite
…vs. extrusive rhyolite

52. Sedimentary Rocks
From hardened sediment

53. Sedimentary Rocks
• The result of erosion, transportation, deposition, and
lithification
• Sediment—Weathered rock fragments that have
been transported and deposited, usually by water (or
by air or by glacial ice movements)

54. Erosion
Mechanical or Chemical
• Mechanical weathering—The physical force of a
particular process acting on rocks, such as hydraulic
action pounding rocks in a riverbed
- OR -
• Chemical weathering—Chemical reactions, usually in
the presence of water, which operate to change the
structure of the minerals, and break them apart
–(Example: iron in the presence of water and oxygen,
incorporating those elements into its structure,
expanding as it becomes rust, breaking rock apart)

55. Transportation
• Distance of transport and speed of the fluid
medium determine size, roundness and
sorting of transported material

56. Deposition
• Deposition generally occurs in flat layers called
strata (or “beds”)
• Principle of Original Horizontality
states that material is originally
deposited in horizontal layers and
later is shifted as it is affected by
crustal movements

57. Sedimentary Rocks
Badlands National Park, SD

58. Horizontal layers
after tectonic movement

59. Lithification
Compaction and cementation
• Lithification is the process of turning
sediment into rock
–As sediment is deposited, the addition of more
layers causes compaction
• (“trash compactor”)
–Dissolved minerals such as silica recrystallize in
pore spaces
–Sediment grains are cemented together

60. Three Main Types of
Sedimentary Rocks
• Clastic (or detrital)
–Formed from pieces of
other rocks
• Chemical
–Dissolved mineral
compounds that solidify
again
(precipitates/evaporites)
• Organic
–Formed from the tissues of
living things

61. Metamorphic Rocks
Any kind of rock subjected to heat and/or pressure

62. Two types of metamorphism
• Regional metamorphism
–Occurs over 100s or 1000s of sq. miles
–Common in subduction zones
• Contact metamorphism
–Localized
–Heat and pressure of rising, intruding magmas
“bakes” surrounding rocks

63. Contact Metamorphism

64. Parent Rock
quartzite gneiss
• Parent rock—Name given to the original rock before
the addition of heat and/or pressure
–what you start with will determine what you end up with

65. Foliation
• The arrangement of mineral crystals into
parallel or nearly parallel bands
–The classification of metamorphic rocks is
generally based on the amount of foliation in the
rock

66. Metamorphic Rock Foliation