Download Interior Crust Hydrosphere Atmosphere Magnetosphere Tides

Earth
Interior
Crust
Hydrosphere
Atmosphere
Magnetosphere
Tides
Semi-major Axis
1 A.U.
Inclination
0°
Orbital period
1.000 tropical year
Orbital eccentricity
0.017
Rotational period
23 h 56 min 4.1 s
Tilt
23° 27’
Radius
6378 km
Mass
5.97 x1024 kg
Bulk density
5.52 g/cm3
Atmosphere
N2, O2
Albedo
0.40
Surface temperature
250-300 K
Escape speed
11.2 km/s
Magnetic moment (equator)
8 x 1010 G.km3
The Early History of
Earth
Earth formed 4.6 billion years
ago from the inner solar nebula.
Four main stages of evolution:
Two sources of heat in the Earth’s
interior:
• Gravitational potential energy of
infalling material
• Decay of radioactive materials
Most traces of early
bombardment (impact craters)
are now destroyed by later
geological activity
Overall Structure of the Earth
• Atmosphere
• Hydrosphere
(oceans)
• Thin, layered
crust
• Mantle—also
divided into
layers
• Two-part core
(solid and liquid)
Earth’s Interior
What can we know about the Earth’s interior from its mass
and size?
Earth’s Mass = MEarth = 5.97 x 1027 g
Earth’s Radius = REarth = 6.378 x 108 cm
Earth’s Volume = VEarth = 4/3 π R3 = 1.1 x 1027 cm3
Earth’s Average Density = ρEarth = MEarth/VEarth = 5.49 g/cm3
ρWater = 1 g/cm3
ρRock = ~3 g/cm3
ρIron = 7 g/cm3
⇒ Cannot be made mostly of water
⇒ Cannot be made mostly of rock
⇒ Can be rock on the outside and iron
on the inside
A planet that has dense material in the interior and light
material on the outside is said to be differentiated.
Differentiation occurs when the whole planet is molten.
Earth’s Interior
Seismic waves are used to explore the Earth’s
interior:
• Earthquakes produce both pressure (P) and
shear (S) waves
• Pressure waves will travel through both
liquids and solids
• Shear waves will not travel through liquid,
because liquids do not resist shear forces
• Wave speed depends on the density of the
material and modulus of elasticity
Earth’s Interior
We can use the
pattern of
reflections during
earthquakes to
deduce the
interior structure
of Earth.
Earth’s Interior
Currently accepted model.
Earth’s Interior
The mantle is much less dense than the core
The mantle is rocky; the core is metallic –
iron and nickel
The outer core is liquid; the inner core is
solid, because of pressure
Some volcanic lava comes from the mantle
allowing us to analyze the composition of
the mantle nearest to the surface (the upper
mantle)
Earth’s Interior
History: Earth was
probably molten when it
formed then the upper
layers solidified and
later remelted because
of bombardment by
space debris. Heavier
materials sank to the
center. Radioactivity
provides a continuing
source of heat.
Crust and Upper Mantle
Continental drift or plate tectonics: The entire Earth’s
surface is covered with crustal plates, which can move
independently
Earthquakes and volcanoes occur at plate boundaries
Plate Tectonics
Crustal plates move with respect to each other.
Where plates move toward
each other, plates can be
pushed upward and downward
⇒ formation of mountain
ranges, some with volcanic
activity, earthquakes
Where plates move away
from each other, molten lava
can rise up from below
forming new crust ⇒
volcanic activity
Plate Tectonics
A plate colliding with another can also raise it by
folding it, resulting in very high mountains
Active Examples:
Himalayas
Alps
Inactive Example:
Appalachians
Plate Tectonics
Plates can also slide
along each other,
creating faults where
many earthquakes occur
Example: San Andreas Fault
Plate Tectonics
Plate motion is driven by convection in the
upper mantle. Mantle material in this zone
is a very viscous liquid like glass
Plate Tectonics
The new crust created at rift zones
preserves the magnetic field present
at the time it solidified. From this,
we can tell that magnetic field
reversals occur about every 500,000
years.
Earth’s Tectonic History
Volcanism on Earth
Volcanism on Earth is commonly found
along subduction zones (e.g., Coast Range
in California).
This type of volcanism is not found on Venus or
Mars.
Shield Volcanoes
Found above
hot spots:
Fluid magma
chamber, from
which lava erupts
repeatedly
through surface
layers above.
All volcanoes on Venus and Mars are shield volcanoes
Shield Volcanoes
Tectonic plates moving over hot spots
producing shield volcanoes ⇒ a chain of
volcanoes
Example: The
Hawaiian Islands
Radioactive Dating

The number of protons
(atomic number) in an
atom’s nucleus determines
which
element
it
is.
However, there may be
different isotopes of the
same element, with the
same number of protons
but different numbers of
neutrons.

Many of these isotopes are
unstable
and
undergo
radioactive
decay. This
decay is characterized by a
half-life T:
Fraction of material
remaining = (1/2)t/T
Radioactive Dating
 Half-lives have been measured in the laboratory for
almost all known isotopes. Knowing these, we can use
them to determine the age of samples by looking at
isotope ratios.
 The most useful isotope for dating rock samples is
238U, which has a half-life of 4.5 billion years,
comparable to the age of the Earth.
 The dating process involves measuring the ratio
between the parent nucleus and the daughter nucleus
(206Pb in the case of 238U)
 The Sun and planets should have about the same age.
 Dating of rocks on Earth, on the Moon, and meteorites
all give ages of ~4.6 billion years.
History of Geological Activity
Surface formations visible today have emerged only very
recently compared to the age of Earth.
Hydrosphere
About 2/3 of Earth’s
surface is covered
by water.
Mountains are
relatively rapidly
eroded away by the
forces of water.
Water makes life possible
on Earth
Earth’s Atmosphere
Surface Heating:
• Sunlight that is not
reflected is absorbed by
Earth’s surface, warming it
• Surface reradiates as
infrared thermal radiation
• The atmosphere absorbs
some infrared, causing
further heating, thus
warming the
troposphere—this is
called the greenhouse
effect
Earth’s Atmosphere
• The blue curve
shows the
temperature at
each altitude
• The
troposphere is
where
convection
takes place –
responsible for
weather
Earth’s Atmosphere
The ionosphere is ionized by high energy
solar radiation. It is a good conductor. It is
heated by absorbed X rays
The ionosphere reflects radio waves in the
AM range, but it is transparent to FM and TV
The ozone layer is between the ionosphere
and the mesosphere; it absorbs ultraviolet
radiation which warms the mesospherestratosphere boundary
Earth’s Atmosphere
Convection depends on
the warming of the
ground by the Sun
Earth’s rotation causes a
Coriolis force that acts on
surface winds
Hadley circulation arises
because of different
latitudinal
heating and the Coriolis
force
Earth’s Atmosphere
The Earth’s Coriolis force
also causes surface winds
to rotate clockwise around
high pressure and
counterclockwise around
low pressure in the
northern hemisphere. It is
the opposite in the
southern hemisphere. This
is baroclinic circulation.
Earth’s Atmosphere
Atmosphere scatters blue light more than red,
making the sky appear blue
Earth’s Atmosphere
When the Sun is
close to the horizon,
light is scattered by
dust in the air. The
more dust, the more
scattering; if there is
enough dust, the
blue light is greatly
diminished, leaving a
red glow in the sky.
How Planets Keep an Atmosphere
Atmospheric molecules have high speeds due to
thermal motion. If the average molecular speed is well
below the escape velocity, few molecules will escape.
Escape becomes more probable:

For lighter molecules (higher speed for same
kinetic energy)

At higher temperatures

For smaller planets
(escape speed is less)
Molecules in a gas have a
range of speeds; the fastest
(and those that are headed in
the right direction) will escape
How Planets Keep an Atmosphere
Loss of gases from a
planet’s atmosphere:
 Compare escape
velocity (red dots) to
typical velocity of gas
molecules (blue lines)
 The planet was
probably hotter in the
past which would shift
the red dots to the right
 Escape velocity less
than gas molecule
velocity ⇒ gas escapes
into space.
History of the Earth’s Atmosphere
• First atmosphere: hydrogen (H2) and helium (He);
this escaped Earth’s gravity
• Second atmosphere: from volcanic activity, mostly
nitrogen (N2), carbon dioxide (CO2) and sulfur
oxides (SOn)
• Third atmosphere:
• Oceans dissolved all the sulfur oxides and some CO2
which may have formed some carbonate rocks
• Plant life appeared, absorbing more CO2 and creating
atmospheric oxygen (O2)
• Bones and shells of sea animals absorbed more CO2 and
their decaying bodies made sedimentary rocks and
completed the absorption of CO2 from the atmosphere
• Nitrogen remained from the second atmosphere
The Greenhouse Effect and
Global Warming
One result of modern society has been to increase CO2
levels in the atmosphere. A corresponding increase in
global average temperature has been seen as well.
Exactly how much the temperature will continue to
increase is not known.
Magnetic Field Lines
Magnetic
North
Pole
Magnetic
South
Pole
Magnetic
Field Lines
Earth’s Magnetic Field
Magnetohydrodynamic Model of
Planetary Magnetic Fields
Three conditions:
1. Conducting
core
2. Rapid rotation
3. Liquid core
⇒ Convection
Earth’s Magnetosphere
The magnetosphere is a magnetic field region around the
Earth where charged particles from the solar wind are
trapped.
The solar wind distorts the magnetosphere in a long tail
that extends beyond the orbit of the Moon.
Earth’s Magnetosphere
Charged particles are trapped in areas called
the Van Allen belts, where they spiral around
the magnetic field lines.
Earth’s Magnetosphere
Near the poles, the Van Allen belts intersect the
atmosphere. The charged particles can escape;
when they do, they create glowing light called an
aurora (pl. aurorae).
The Tides
 Caused by the
Moon’s differential
gravitational attraction
of the water on the
Earth
 Forces are balanced
at the center of the
Earth
 Excess gravity pulls
water towards the
Moon on the near
side
 Excess centrifugal
force pushes water
away from the Moon
on the far side
⇒ 2 tidal maxima
⇒ 12-hour cycle
Spring and Neap Tides
Spring tides
The Sun also
produces tidal forces,
about half as strong
as the Moon.
• Near full and new
Moon, those two
forces add up to
cause spring tides
Neap tides
• Near first and third
quarter, the two
forces work at a
right angle, causing
neap tides.
The Tides
Tidal
(differential)
forces have
important roles
for many
astronomical
situations,
including the
rings of giant
planets