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Chapter 2
Journey to the Center of the
Earth
•
The Earth’s
magnetic field is a
dipole magnet. This
means it has a north
and a south pole.
The force generated
by a magnetic field
repels charged
particles.
• Magnetic field
lines show
trajectories along
which magnetic or
charged particles
would flow.
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•
The solar wind contains electrically charged particles that are deflected by the
Earth’s magnetic field. The magnetosphere is the region inside this shield.
•
The Van Allen radiation belts (located 3,000 km and 10,500 km out from
the Earth) are important because they trap those solar wind particles and
cosmic rays that get through the magnetosphere that would otherwise
bombard the Earth with dangerous radiation.
The atmosphere is a very thin
layer that surrounds the earth
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The atmosphere is mostly nitrogen and oxygen with a small proportion of trace
gases (labeled as other gases on the diagram). Trace gases consist of compounds
like carbon dioxide (CO2) and methane (CH4). Although trace gases are present in
very small amounts, they play important roles in climate warming because they
tend to absorb and reflect back to the surface long-wave radiation, thus promoting
heating..
Venus and Mars
both have
atmospheres
made up of CO2
gas.
Pressure and temperature increase with depth in the Earth. At the center of the
Earth, pressure is 3.6 million times greater than at the surface and temperatures can
reach 4,300oC, nearly as hot as the Sun’s surface. The rate of temperature change
with depth is called the geothermal gradient.
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•
The troposphere is the lowest layer of the atmosphere and this is where
air undergoes convection. Convection refers to the circulation that
occurs when different parts of a fluid have different temperatures.
Warm air rises, cooler air sinks. Convective cells also occur deep
within the earth where warm, melted rock rises, then sinks as it cools.
•
Land covers about 30% of the Earth’s surface, oceans 70%.
•
Groundwater is all surface water plus the water that fills the openings
underground. The hydrosphere is that plus the water vapor in the
atmosphere.
•The topography of the Earth shows different kinds of landscapes such as
mountains, valleys, and plains. There are also submarine plains, oceanic ridges,
and deep trenches beneath the ocean.
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•The solid earth is
mostly made of iron
(35%), oxygen
(30%), silicon
(15%), and
magnesium (10%).
The remaining 10%
consists of the other
88 naturallyoccurring elements.
The lighter elements
were blown away
by the solar wind
during the formation
of the Earth and
other planets.
Categories of earth materials
•
Carbon-containing compounds are generally called organic chemicals (oil,
protein, fat, plastic, and rubber). Carbon-containing compounds such as pure
carbon (C), carbon dioxide (CO2), carbon monoxide (CO), lime (CaO)and calcium
carbonate (CaCO3) are considered inorganic.
•
Minerals are a solid inorganic substance where the atoms are arranged in an
orderly pattern or crystalline lattice (example: quartz, feldspar, diamond, calcite).
Precipitation occurs when dissolved atoms come together to form a solid.
A crystal is a single coherent example of a mineral.
A grain is a fragment of a mineral.
Rocks are aggregates of crystals or grains.
Igneous rocks crystallize from molten rock.
Sedimentary rocks arise from the cementation of loose grains (sand, mud, etc.)
and through chemical precipitation (from the ocean or bodies of water).
Metamorphic rocks arise from heat and pressure-induced alteration of existing
rock (without melting).
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Categories of earth materials (cont’d)
• Glasses are physical solid structures in which the atoms are disordered (for
example, obsidian, commercial glass). These materials were cooled very
quickly from the molten to the solid state thus not allowing the atoms to order
themselves into a lattice structure.
• Metals are solids comprised of metallic elements only such as gold, iron, and
copper.
• Melts are hot liquids that crystallize at surface temperatures to form igneous
rocks. When they occur within the Earth, they are called magma. Extruded
melts are called lava.
• Volatiles are substances that are stable in a gaseous state at the Earth’s
surface.
• The Earth’s Interior – a layered sphere
• The Earth’s interior consists of a series of layers that are called (1) the
crust, (2) the mantle, and (3) the core. The crust is a relatively thin
skin (7-10 km beneath oceans, 25-70 km beneath the land surface) over
the mantle. There are two kinds of crust:
• Oceanic crust consists of basalt (mafic, meaning iron-rich, rock).
• Continental crust is intermediate to silicic.
• The mantle, (ultramafic rock) can be divided into 3 layers: upper
mantle, transition zone, and lower mantle. The crust and the upper
mantle are known as the lithosphere. The underlying, warmer and
more plastic portion of the mantle is known as the asthenosphere.
• The inner core can be divided into an outer core of liquid iron alloy and
an inner core of solid iron alloy. Within the Earth’s outer core, there is
convective flow and that flow, it is believed, is what creates the Earth’s
magnetic field.
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What is an earthquake?
•
When rock within the crust suddenly breaks, an earthquake results. An
earthquake is a vibration. This vibrational energy moves as seismic waves.
Earthquakes can produce a new fracture in the earth’s crust or can cause
sliding or movement on an existing fracture. Sliding on a existing fracture
is called a fault.
•
The speed at which seismic waves travel can change abruptly beneath the
surface. The boundary at which the velocity changes is called a seismicvelocity discontinuity. This represents a pronounced change in the nature
of the material comprising the earth, such as a change in density or
compressibility.
•
Major discontinuities define the boundaries between the mantle and the
core. The Moho seismic discontinuity defines the boundary between the
crust and the mantle..
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The Crust
• Oceanic crust underlies the sea floor and is less than
10 km thick. It is composed primarily of mafic (ironrich) igneous rocks.
• Continental crust ranges from 25 km thick to more
than 70 km thick and can contain a variety of rock
types but, on average, is less mafic and more silicic
than oceanic crust. Rocks that are more mafic tend to
be heavier than silicic rocks. The continental crust
“float” on the asthenosphere because it is less dense
and lighter in relation to the more mafic and heavier
oceanic crust. Continental crust usually consists of
rocks different from the mantle.
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The Mantle
• The Earth’s mantle is about 2,885 km thick and is the largest part of the
Earth. The mantle is made up of ultramafic rock called peridotite, a rock rich
in iron and magnesium but poor in silica.
• The mantle consists of the upper mantle (to 400 km), the transition zone
(400 km to 670 km), and the lower mantle (670 km to the core boundary).
Mantle rock is relatively solid but can also flow very slowly (like softened
wax).
• There is a region below the ocean basins called the low-velocity zone where
up to 2% of the mantle has melted and exists as droplets of molten rock
between solid grains.
• Temperature in the mantle generally increases with depth but not uniformly.
This creates a convective flow pattern.
• The mantle composition consists mostly of iron and magnesium-rich
minerals.
The Core
• There is an outer core (between 2,900 and 5,155 km deep)
and an inner core (from 5,155 to 6,371 km).
• The outer core is a liquid iron alloy because of the
extremely high temperatures in that region.
• The flow of the outer core generates the Earth’s magnetic
field.
• The inner core is a solid iron alloy, despite the high
temperatures, because of the tremendous pressure it is
subjected to.
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End of Chapter 2
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