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Hot spots and plate tectonics
I. Hot spots
Stationary hot spots
on Earth where heat
rises (not at plate
boundaries)
Hot spots produce
volcanoes in plate
interiors.
Remain fixed relative
to moving plates.
Hot spots, Geologic Time & Rock Cycle
I. Hot spots
B. Heat rising at hot spots
melt rock in the crust—it
rises and erupts.
As the lithosphere moves
over the hot spot it takes the
newly formed volcanic
edifice with it.
1. Seamounts - underwater
volcanoes on sea floor
2. Volcanoes - have reached
the water’s surface
3. guyots (ghee-owes) - not
active any more, have
eroded down below sea
level
Hot spots, Geologic Time & Rock Cycle
I. Hot spots
C. As the plate moves, the
hot spot forms a chain of
volcanoes—records
plate motion
1.Hawaii 6000km long
(4000 miles)
a. Kaua’i is the oldest Hawaiian island—5.1 million years old
b. Hawaii is the youngest—still over the hot spot
c. Loihi is a seamount, will be the next Hawaiian island (currently is ~9,000
feet tall from the seafloor, and still has several thousand meters to go
before it reaches sea level—a few hundred thousand years
Hot spots, Geologic Time & Rock Cycle
Hot spots, Geologic Time & Rock Cycle
I. Hot spots
C. As the plate moves, the
hot spot forms a chain of
volcanoes—records plate
motion
As the moving plate carry
each island away from the
hot spot, the volcanoes
loss their heat source and
become extinct.
Weathering and erosion
gradually reduce the
heights of the volvanoes
above sea level.
II. Geologic Time
A. Earth is ~4.6 billion
years old
1. Earth timeline across
the US, each kilometer
is ~1million years
Time line across USA, 1 km = 1 Myr
Hot spots, Geologic Time & Rock Cycle
2. History of Earth all in a
year:
- Oldest rocks—mid-March
- First life in the sea—May
- Land plants and animals—
November
- Dinosaurs became
dominant—Mid-December
- Dinosaurs extinct—
December 26th
- Manlike creatures first
started walking—evening of
Dec 31st
- Roman Empire—Dec 31st, 5
seconds: 11:59:45-11:59:50
- Columbus discovered
America—3 seconds before
midnight
Hot spots, Geologic Time & Rock Cycle
B. Divisions of Geologic
Time: based on fossils,
so not equal amounts of
time
Earth history is divided
into blocks of time during
which important events
occurred
Based on fossils ages
assigned to the divisions
using isotopes in the later
part of 20th century
Time blocks are not equal
lengths of time
see page 290 in book
Geologic Time
4 Eons—largest spans of time
 Hadean (beneath Earth) oldest,
4.6 – 3.8 bya. Few rocks of this
age left
 Archean (ancient) 3.8 – 2.5 bya
Earliest life on earth (bacteria 3.77
bya) (single-celled org 3.3 bya)
 Proterozoic (early life) 2.5 bya –
545 mya. First multi-celled
organisms
 Phanerozoic (evident life) 545
mya – present
Geologic Time
3 Eras in the Phanerozoic:
Divided based on dominant forms
of life
 Paleozoic: 545 – 245 mya age
of invertebrates, fish, and
amphibians
 Mesozoic: 245 – 66.4 mya age
of reptiles
 Cenozoic: 66.4 – present age
of mammals
Geologic Time
12 Periods in the Phanerozoic
Less dramatic biological
changes
Cambrian
Ordovician
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Triassic
Jurassic
Cretaceous
Tertiary
Quaternary
Rock Cycle
III. Rock Cycle
A. Definitions
1. Rock: naturally formed
aggregate of one or more
minerals
2. Mineral: naturally occurring
inorganic solids with a definite
chemical composition
SiO2, CaCO3, Fe2SiO4, BaSO4,
PbS
3. Rock Cycle—describes the
processes by which the
various rock types change
over time
Rock Cycle
The Rock Cycle
1. Magma—molten (liquid) rock
that forms in certain places in
the Earth’s interior where
temperatures and pressures
are such that rock melts
- migrates up into crust
2. Crystallization - magma cools
and solidifies
a. It can erupt in a volcano and
then it cools at the Earth’s
surface - extrusive
b. Or it crystallizes underground intrusion
3. Igneous rocks - have cooled
and solidified from molten
material (lava or magma) either
at or beneath the Earth’s
surface
Rock Cycle
4. Weathering: any rock exposed at
the Earth’s surface will undergo
weathering - daily influences of
the atmosphere slowly
disintegrate & decompose rocks
5. Sediment: particles of rock and
dissolved substances that have
been removed from their original
outcrop & transported.
a.
b.
c.
Sediments range in size from
atoms dissolved off by acid rain
to boulders
Transported by erosional
processes: running water,
glaciers, wind, waves, etc.
Deposited: usually in the ocean,
but sometimes in river
floodplains, desert basins,
swamps, and sand dunes.
Rock Cycle
6. Lithification—“conversion
(sediment) into rock”
a. Compacted by weight of overlying
sediment
b. Cemented together when
percolating water fills the pores
with minerals
7. Sedimentary Rock: rock made
up of sediment that has been
lithified
a. Can also form from the
accumulated and compressed
remains of certain plants and
animals (shells in oceans & plants
in swampscoal)
b. Also from chemical precipitates of
minerals previously dissolved in
water (salt)
Rock Cycle
8. Metamorphism
 When rock is buried deep in the
earth, it is subjected to intense
heat and pressure
 The rock changes mineralogy,
chemical composition, and
structure without melting (peanut
butter and jelly sandwich
example)
9. Metamorphic rocks
10. Melting: any rock if subjected to
enough heat will melt (given that
the pressure isn’t too high)
Rock Cycle
8. Metamorphism
 When rock is buried
deep in the earth, it is
subjected to intense
heat and pressure
 The rock changes
mineralogy, chemical
composition, and
structure without melting
(peanut butter and jelly
sandwich example)
9. Metamorphic rocks
10. Melting: any rock if
subjected to enough
heat will melt (given that
the pressure isn’t too
high)
Rock Cycle
C. Alternative routes:
a. igneous rock 
metamorphic rock
b. metamorphic rock 
sediment
c. sedimentary rock 
sediment