Chapter 11
The Dynamic
Planet
Robert W. Christopherson
Charlie Thomsen
The seemingly static landscape and mountains are
constantly being shaped and reshaped by endogenic and
exogenic forces, although slowly. Given enough time,
any slow process can make a difference.
The Dynamic Planet
The Pace of Change
Earth’s Structure and Internal Energy
The Geologic Cycle
Plate Tectonics
The Pace of Change
Geologic time scale
Popular time: 1500 BC, 2009AD
Years Before Present (BP):
Uniformitarianism: An assumption that the
same physical processes active in the
environment today have been operating
throughout geologic time.
Geologic Time Scale
Earth age: 4.6 billion years
condensed and congealed from a nebula
of dust, gas and icy comets.
Scales of Geologic Time
Eons:
Eras:
Periods:
Epochs:
Zoic: life
Protero-: former, anterior
Phanero-: visible to the naked eye
flowering plants
Paleo-: old
Meso-: middle
Ceno-: recent
Figure 11.1
Earth’ Time Clock: Radioactivity
Atom:
nucleus: protons (+) & neutrons
electrons (-)
For some matter, its protons and neutrons do not stay together indefinitely.
The particles can break away and the nucleus can disintegrate and
form new matter, in the mean time release radioactive energy. The
decay rate is measured by half time, the time needed for the matter to
decay half of its mass into new matter.
Measuring the ratio of original matter and its decayed matter, one can
estimate the age of the object.
The oldest rock dated: 4.3 b.y.a, indicating continental crust was forming
this many years ago.
Earth’s Structure and Internal Energy
Earth’s Core :
Inner Core
Outer Core
Earth’s Mantle:
Lower Mantle
Upper Mantle
Asthenosphere
Uppermost Mantle
Crust: Continental and Oceanic Crust.
Earth in
Cross Section
Figure 11.2
Earth’s Interior
Figure 11.2
Earth’s Interior
Mantle includes lower and upper (upper
mantle, asthenosphere and uppermost mantle)
mantle, representing 80% of Earth volume.
Temp increase with depth. Rich in oxides of
iron, magnesium and silicates.
Note the density gradient
Outer core generate 90% of Earth magnetic
field to form magnetosphere, which protects
Earth from the solar wind and cosmic
radiation.
Inner core remains solid iron because of
tremendous pressure though temp well above
melting point,
Figure 11.2
As Earth solidified,
gravity sorted materials
by density. Heavier
substances (e.g. iron)
gravitated toward the
center; lighter elements
(e.g. silica) welled upward
to the surface.
Earth’s Interior
Continental crust: primarily granite
high in silica, aluminum, potassium,
calcium and sodium
Oceanic crust: primarily basalt high
in silica, magnesium and iron
Lithosphere: Crust +
uppermost mantle.
Asthenosphere: plastic layer (least
rigid in mantle), contains hot spots
causing vertical convection, creates
tectonic activity
Figure 11.2
Core to Crust
Figure 11.3
How Scientists Know the Deep Structure?
Scientists cannot dig that deep. The deepest hole scientists
ever dug is 12.23km (20 years of effort!)
Scientists infer the deep Earth structure indirectly through
seismic tomography. The rate of transmittance of seismic
waves depends on the density of the structural material.
Rigid matter transmits the seismic waves faster. Plastic
zones simply do not transmit certain seismic waves. Some
seismic waves are reflected when density changes, whereas
others are refracted (or bent) as they travel through Earth.
Earth’s Magnetism
 At least 90% of Earth’s Magnetism is generated by fluid
outer core.
 Magnetic North is at 83o N, 114oW in 2005. Magnetic
north pole migrates. It moved 1100 km in the past century.
 Magnetic reversal: Magnetic polarity sometimes fades to
zero and returns to full strength with magnetic poles
reversed. It happened 9 times in the past 4 million years.
The transition period between reversal is relatively short
(1,000 ~10,000 years)
 Current records indicates that magnetic fields decay over
the last 150 years. We may be within 1000 years of
magnetic reversal.
Isostatic
Adjustment
Continental crust is lightest,
“floating” on denser layers. When
there is heavier loads, such as
mountains, glaciers, , the crust
“sink” deeper (like a boat loaded
with cargo). Unloading these cargos
will results in isostatic rebound as
shown here.
GPS can be used to study the rate
of isostatic rebound. A group of
scientists from UAF found that
southern Alaska is rebounding
much faster than they thought
because of melting of glaciers
Figure 11.4
The Geologic Cycle
Rock Cycle
Minerals and Rocks
Igneous Processes
Sedimentary Processes
Metamorphic Processes
The Geologic Cycle
The cycle of
matter within the
Earth system
caused by
exogenic and
endogenic forces.
Hydrologic Cycle
Rock Cycle
Tectonic Cycle
Figure 11.5
The Geologic Cycle
Figure 11.5
Eight natural elements make up 99% of Earth’s crust! Oxygen and Silicon make up 74.3%. There are
more Oxygen in the crust (47%) than in the atmosphere (21%) !
The Rock
Cycle
Figure 11.6
Plate Tectonics
A Brief History
Sea-Floor Spreading and Production of New
Crust
Subduction of the Crust
The Formation and Breakup of Pangaea
Plate Boundaries
Earthquake and Volcanic Activity
Hot Spots
A Brief History of Plate Tectonics
First person to notice the apparent fit of some
continental coastlines was a Geographer
(Abraham Ortelius) in 1500s.
The “continental drift” concept was formally
introduced by a German geophysicist,
Alfred Wegener in 1915. The Earth had a
single giant continent, Pangean 225 MBP,
then drifted apart as we have today.
Wegener’s continental drift concept was
confirmed in the 1960s.
Crustal Movements:
Sea Floor Spreading
A remarkable feature of the sea
floor:
An interconnected worldwide
mountain chain, forming a ridge
~64,000 km in length and ~1,000
km in width.
Figure 11.13
Magnetic Reversals
Evidence of sea floor spreading:
1. The magnetic particles orient themselves in line with the magnetic fields when the
lava appeared and its orientation is frozen in the rocks.
2. Radioactive dating: the farther away from the ridge, the older the age of the rocks.
Figure 11.14
Relative Age of the Oceanic Crust
The oldest sea floor rock is 208 MBP (quite young compared to
4.6 Billion years of Earth).
Figure 11.15
Continents Adrift
Three kinds of plate boundaries:
7 major plates:
Figure 11.16
Earth’s Major Plates
Arrows represent 20
million years of
movement.
Figure 11.17
Earthquakes and Volcanoes
: upwelling material arrive at the surface
Plate boundaries are the primary location of earthquake and volcanic activity
Figure 11.20
Hot Spot Tracks
Another hot spot: Yellow Stone
National Park: a mega-magma
chamber beneath which explodes
620,000 years. It can explode in the
next 20,000 years. It is so big its
ashes can cover half the country.
Figure 11.21
End of Chapter 11
Geosystems 7e
An Introduction to Physical Geography
Robert W. Christopherson
Charlie Thomsen