1. The LithosphereThe Lithosphere
Chapter 9Chapter 9

2. Geologic Time vs. Human TimeGeologic Time vs. Human Time

3. 3
How do we date rocks?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 gives
a date (1:1 means one half-life has passed) 3

4. 4
The oldest rocksThe oldest rocks
 Earth first condensed and formed into aEarth first condensed and formed into a
planet about 4.6 billion years ago.planet about 4.6 billion years ago.
 Oldest rocks are from the Acasta Gneiss inOldest rocks are from the Acasta Gneiss in
northwestern Canada: 3.96 billion years oldnorthwestern Canada: 3.96 billion years old
 OldestOldest grainsgrains of rock, from Western Australia:of rock, from Western Australia:
bet. 4.2 and 4.4 billion years oldbet. 4.2 and 4.4 billion years old
 Will we ever find large pieces of the oldestWill we ever find large pieces of the oldest
rocks or rocks that are even older?rocks or rocks that are even older?
4

5. Earth’s Interior StructureEarth’s Interior Structure

6. From the crust on downFrom the crust on down

7. 77
Earth’s magnetic fieldEarth’s magnetic field
• Circulations within Earth’s inner and outer
cores are thought to 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
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8. 88
Which elements make upWhich elements make up
Earth’s crust?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
88
These elements, and trace others, combine to
make up Earth’s minerals and rocks...

9. 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.

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

11. ...naturally-occurring...
• Diamonds

12. ...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

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

14. ...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?

15. 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

16. 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

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

18. 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
– Diatoms and radiolarians in the
ocean
• Silicate minerals
• Their skeletons are used as polishing
agents...
...(in your toothpaste!)

19. Is coal a mineral?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
But…They can form minerals under certain conditions
–If coal beds are heated to high temperatures and
the carbon in them is crystallized, they can form
the mineral, graphite

20. Mineral Formation:Mineral Formation:
Non-organic formationNon-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)

21. From cooled magma

22. From steam: vaporitesFrom steam: vaporites
• Vaporite
–Water near a magma source heats up, dissolves
mineral components
–Mineral compounds “condense” and solidify at the
surface
Commonly found around
volcanic vents, these sulfur
crystals are forming around
Kilauea Crater, Hawaii. Also
found near oceanic volcanic
vents.
Harvesting sulfur crystals from a volcano in Indonesia

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

24. From evaporating water: evaporitesFrom evaporating water: evaporites
• Evaporite
–Water evaporates, leaving behind mineral
compounds dissolved in the water
Salt crystals like these form in
salt beds along the edge of
Highway 84, just before the
Dumbarton Bridge.

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

26. Experiment
• Make a precipitate mineral at home...

27. 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

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

29. What is a Rock?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
• Example: massive accumulations of halite

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

31. The Rock CycleThe Rock Cycle

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

33. Convection CurrentsConvection Currents

34. The 3 Classes of RockThe 3 Classes of Rock
• Classified based on the processes which
form them
–Igneous rocks
–Sedimentary rocks
–Metamorphic rocks

35. Igneous RocksIgneous Rocks
from cooling magmasfrom cooling magmas
from cooling magmasfrom 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

36. Felsic MagmasFelsic 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
• 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)

37. 3737
Felsic rocksFelsic rocks
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38. Felsic MagmasFelsic Magmas
Explosive Mount St. HelensExplosive Mount St. Helens
(Pre-eruption)

39. Felsic MagmasFelsic Magmas
Explosive Mount St. HelensExplosive Mount St. Helens
(May 18, 1980)(May 18, 1980)

40. Felsic MagmasFelsic Magmas
Explosive Mount St. HelensExplosive Mount St. Helens
Mt. St. Helens Today

41. • 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 RocksMafic Minerals and Rocks

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

43. Intrusive vs. ExtrusiveIntrusive vs. Extrusive
Igneous RocksIgneous 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”)

44. Extrusive Igneous RocksExtrusive Igneous Rocks
Basalt and ObsidianBasalt and Obsidian

45. Intrusive Igneous RockIntrusive Igneous Rock
GraniteGranite
…vs. extrusive rhyolite

46. Sedimentary RocksSedimentary Rocks
From hardened sediment

47. Sedimentary RocksSedimentary 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)

48. Erosion:Erosion:
Sediment is made throughSediment is made through
Mechanical or Chemical WeatheringMechanical or Chemical Weathering
Mechanical or Chemical WeatheringMechanical or Chemical Weathering
• Mechanical weathering—The physical force of a
particular process acting on rocks, such as water
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)

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

50. DepositionDeposition
• 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

51. Sedimentary RocksSedimentary Rocks
Badlands National Park, SDBadlands National Park, SD

52. Horizontal layersHorizontal layers
after tectonic movementafter tectonic movement

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

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

55. Two types of metamorphismTwo types of metamorphism
• Regional metamorphism
–Occurs over 100s or 1000s of sq. miles
–Common in subduction zones (where crustal
plates collide)
• Contact metamorphism
–Localized
–Heat and pressure of rising magmas “bakes” the
surrounding rocks

56. Contact MetamorphismContact Metamorphism