How does the Earth work?
Earth Cycles
The rock cycle
The hydrologic
cycle
The flow of
nutrients, elements, and energy
Climate cycles –
global climate change
Sea-level cycles
How does the Earth work?
The one main answer:
Plate tectonics
How did the Earth get here?
Processes
of forming the solar system, igniting the Sun, forming planetesimals, then
protoplanets
What are the ultimate sources of energy on this planet?
Earth
surface – almost entirely driven by solar energy
Earth
interior – heat produced by decay of radioactive elements
How does geology help society?
Natural hazards
Efficient use of
resources
Construction and
planning
Understanding
the impacts of human activities
What is inside the Earth?
Basic
layers of the Earth – crust, mantle, core
Different
set of layers when considering plate tectonics:
lithosphere, asthenosphere, mesosphere, core
How can we infer what is inside the Earth?
Seismographs
all around the Earth (on the surface) record the way seismic waves are
transmitted through the Earth interior.
Remember the difference between P (primary, pressure) and S (secondary,
shear) waves.
Why does the Earth have magnetic poles?
The solid
inner core spins slightly faster than the rest of the planet inside the liquid
outer core. This acts as an electric
generator to produce a strong electromagnetic field that extends out into
space.
What drives plate tectonics?
Fundamentally,
mantle convection. Heat and hot rock
that circulate through the mantle.
Cold, dense slabs are recycled back into the mantle by subduction.
What is continental crust made of? Oceanic crust?
Continental
crust and oceanic crust are fundamentally different.
Continental
crust is old (billions of years), thick (20 to 50 km), lower density, and
granitic, whereas, oceanic crust is relatively younger (no more than 200
million years), thin (5 to 15 km), higher density, and basaltic.
The surface
of the planet has two basic elevations that represent the continental blocks
and the ocean basins.
How does seismic energy move through the Earth?
The rapid movement of two plates or pieces of
rock during an earthquake produces P and S waves that radiate away from the
focus of the earthquake spherically through the body of the Earth. These seismic waves may intersect the land
surface, where they change form and become surface waves, analogous to the
waves on the ocean.
What happens to rocks when force is applied to them?
Stress is
the force applied to a rock. Strain is
the resulting deformation.
Force can
produce compressional, extensional, or shearing strain.
The outcome
depends on the rate of force applied, and the properties of the rock. Rapid stress on brittle rocks creates
faults, slow stress on ductile rocks produces stretching, squishing, or
folding.
What are faults?
The result
of brittle failure of rock.
Types of
faults: normal, reverse, strike-slip,
dip-slip, oblique-slip
Are earthquakes distributed randomly?
Earthquakes,
and volcanoes, occur mostly at plate boundaries.
Shallow
earthquakes occur at divergent and transform boundaries; intermediate and deep
earthquakes occur at convergent boundaries.
Why does San Francisco have earthquakes?
San
Francisco Bay is bounded by two major faults:
the San Andreas fault to the west and the Hayward fault to the
east. This is part of a large-scale
transform system that stretches from the Gulf of California to Cape Mendocino.
What is a tectonic plate? How many major plates are there?
A tectonic
plate is made of the crust and the uppermost part of the mantle that has cooled
and welded onto the bottom of the crust – this is the lithosphere. The plates slide across the “hot silly
putty” layer of the asthenosphere.
Each
continent is associated with a major tectonic plate, plus the Pacific plate,
which is the only plate that does not have a significant chunk of continental
crust. So, the major plates are:
North
American, South American, African, Eurasian, Indo-Australian, Antarctic, and Pacific.
What are the three types of plate boundaries?
What happens at each?
Divergent –
spreading, mid-ocean ridges and rift valleys like the East African Rift Valley
Convergent
– subduction and collision, trenches and mountain ranges
Transform
or displacement – plates slide laterally past one another, transform faults
such as the San Andreas
How do we know the seafloor is spreading?
One of the
main pieces of evidence is the pattern of magnetic anomalies parallel to the
rift valley of the mid-ocean ridge.
When matched with the paleomagnetic record, these magnetic anomalies can
be used to interpret the age of the entire ocean floor.
How old is the seafloor?
The cycle
of oceans forming and closing takes about 200 million years. The oldest known pieces of the seafloor are
along the western margins of the Atlantic and Pacific Oceans, and are about 160
and 180 million years old, respectively.
What creates mountain ranges?
Continental
collisions. The most obvious “recent”
example is the collision of the subcontinent of India into Asia, to produce the
Himalayas and the Tibetan Plateau.
What is a rock? What is a mineral?
A rock can
be made of one or more minerals. An
example of a single-mineral rock would be rock salt, or halite (the
mineral). Most rocks are made of groups
of minerals (igneous and metamorphic rocks) or particles of other rocks
(sedimentary rocks).
A mineral
is a naturally occurring solid, with a specific chemical composition, and, most
importantly, a repeating structure of atoms.
How do the structure and composition of silicate minerals relate to pressure and temperature conditions inside the Earth?
Bowen’s
reaction series describes the path taken by cooling magmas. The discontinuous branch has discrete
silicate minerals that melt and freeze at specific temperatures. This branch proceeds from olivine at high P
and T through pyroxene, amphibole, and mica, to quartz at low P & T. The continuous branch, comprising the
feldspars in a solid-solution series, changes from Ca, to Na, to K feldspars,
in varying percentages through the range of pressure and temperature.
Bowen’s
reaction series run in reverse explains the resistance to weathering of the
various minerals at the Earth surface, and the order of metamorphism when rocks
at the surface are buried and heated.
How does magma form? Where does it come from?
Depending
upon the tectonic setting, magma may be produced directly from the mantle
(mid-ocean ridges and hotspots such as Hawaii), or by melting the rocks of the
lower lithosphere (above the descending plate in a subduction zone).
Compare the formation of magma at a divergent boundary with a convergent boundary.
Very different processes, and different types of
magma produced. Basaltic magma at
mid-ocean ridges, intermediate and/or granitic magma at subduction zones.
What are the most important, simple, characteristics used to classify igneous rocks?
Composition and texture.
Texture relates to the rate of cooling:
small crystals form when the magma cools quickly near the Earth surface,
large grains form when the magma cools slowly, deeper, as in a pluton or
batholith.
Why does Mt. St. Helens explode, but Mauna Loa flow?
Different
magmas with different properties. The
intermediate magma of Mt. St. Helens is viscous because it has a lot of silica,
and explosive because of the high content of water vapor and other
volatiles. In contrast, the basaltic
lava of Mauna Loa has little silica and few volatiles.
Where does sediment come from?
Sediment is produced by breaking up rocks into
little pieces (clasts). The key
processes are weathering and erosion.
What processes break up rocks?
Physical
processes such as ice wedging, abrasion (by particles carried by wind, water,
or ice), roots, freeze-thaw, and effects of gravity. And chemical processes such as attack by acids, hydration (adding
water), and oxidation (adding oxygen).
What is soil? Are
there different types of soil?
Soil is a
mixture of inorganic sediment grains and organic material. There are different types of soil, depending
mostly on the parent material (rock or sediment), climate, slope of the land
surface, and drainage
What sediments would you expect to find in:
Lake Erie
Death
Valley
Bahamas
Continental
shelf of Antarctica
Cape
Hatteras
Describe a trip down the North Platte River
, from the Rocky Mountains, across the Great Plains, and down the Missouri and Mississippi Rivers to the Mississippi Delta.
What can happen on the Earth in
1000 years
100,000 years
1 million years
100 million years
1 billion years
5 billion years
10 billion years