Download (a) evaluate heat transfer through Earth`s subsystems by radiation

(9) Solid Earth. The student knows Earth's interior is
differentiated chemically, physically, and thermally. The
student is expected to:
(a) evaluate heat transfer through Earth's
subsystems by radiation, convection, and conduction
and include its role in plate tectonics, volcanism,
ocean circulation, weather, and climate;
Greenhouse effect (radiation)
Deep sea vs. surface currents
(b) examine the chemical, physical, and thermal
structure of Earth's crust, mantle, and core,
Including the lithosphere and asthenosphere;
Earth’s internal structure
Earth’s subsystems include:
• the
• the
• the
• the
Contains all of the planet’s land, and rocky
lithosphere surfaces…which may be beneath the ocean.
the envelope of protective gases
atmosphere Contains
which surround the planet.
hydrosphere Contains all the water on the planet, which
can be solid, liquid, and gas.
biosphere Contains all of the planet’s living things, animals
and plants, fungi, bacteria, and protists.
Thermal energy from the sun is transferred through
each of these subsystems in three ways.
• Conduction
• Convection
• Radiation
In the Lithosphere:
The conduction of heat slowly
through the outer layers of the
lithosphere, causes it to cool and
thicken over time.
Conduction is the transfer of
heat energy between two objects
that are in direct contact with
In the Atmosphere:
The atmosphere is an EXTREMELY
each other. Walk on a sidewalk
poor conductor of heat energy, and
with bare feet in the summer and only the first few millimeters above
the Earth’s surface are capable of
you know about conduction.
it.
Dive into a swimming pool, and
In the Hydrosphere:
you know about conduction.
The better the conductor, the
faster the heat energy will
transfer.
Objects and substances that do
not make good conductors are
called insulators.
The hydrosphere is also EXTREMELY
poor at conducting heat energy, and
again, only the regions close to the
surface of the Earth conduct heat
energy efficiently
In the Biosphere:
The Earth’s terrestrial surface is
obviously linked to the atmosphere by
conduction. Once the surface is
heated by radiant energy, it can be
transferred to organisms…or through
simple body-to-body contact.
In the Lithosphere:
Convection is the “up and
down” movement of fluids
(both gases and liquids) that
is caused by heat transfer.
As gases and liquids are
heated, they expand and
rise, and become less dense.
As they cool they contract,
and sink…and become more
dense. This rising and
falling motion is called a
“convection current”.
As the lithosphere is the rigid, rocky,
outermost portion of our solid planet, it
does not convect heat energy. Only fluids
transfer energy through convection.
In the Atmosphere:
Heat gained by the lowest layer of the
atmosphere from radiation or conduction is
most often transferred by convection.
Convective motions in the atmosphere are
responsible for the redistribution of heat
from the warm equatorial regions to higher
latitudes and from the surface upward
In the Hydrosphere:
Energy from the Sun heats the Earth’s
surfaces unevenly. As a result, convection
currents develop in the oceans. These
redistribute heat in oceans.
In the Biosphere:
The biosphere is not directly affected by
convection, but given the high degree of
interconnection between different Earth
subsystems, convection indirectly affects
the biosphere in the air, and waters
Convection occurs in Earth’s mantle, as directed by the
internal heat furnace of the Earth’s interior. Remember,
some of this heat energy is left-over from the accretion
process. Most of it, however, is a direct result of the
radioactive decay of the heavy Earth elements such as
plutonium, and uranium.
The thermal structure
of the Earth’s interior
is impressive, and at its
core, the temperature
is as hot as the outer
surface of the Sun.
Certainly, enough heat
energy to drive the
tectonic plates on
Earth’s surface!
In the lithosphere,
biosphere, and hydrosphere,
When electromagnetic energy radiant energy has an
indirect role, as radiation
waves move through the
vacuum of space from a star, moves most readily through
space. This radiant energy
as soon as they come into
contact with a planet or other is transferred to Earth’s
object, the waves transfer the surfaces, and transformed
into thermal energy and
heat to that object.
chemical energy. It can
either be absorbed, or reradiated back to space.
Our sun produces
electromagnetic waves that The Atmosphere
move through space and strike The atmosphere has the capacity to
and transmit the Sun’s radiant
the Earth (and all the objects accept
energy. Radiation occurs through any
in our Solar System). This
transparent medium (solid or fluid) but
also occurs across a vacuum. We feel the
warms the Earth.
warmth of the Sun on a summer day
because of radiation.
The hydrologic cycle
is driven by the
Sun’s energy.
• Evaporation
• Condensation
• Precipitation
• Infiltration
• Transpiration
• Runoff
Solar energy input dominates the surface processes (wind, weather,
climate, ocean circulation, etc.) of the Earth, and because the Earth is
a sphere, its input is not uniform across the planet. The concentration
of solar energy depends on the angle at which the solar radiation
arrives. In equatorial regions, where the sun's rays come in close to
perpendicular, a maximum amount of heat is received. In polar regions,
on the other hand, the sun's rays come in slanted at a shallow angle and
considerably less heat is received.
With deep ocean currents, we see another
“mock” convective current. “Mock”, because
it is only indirectly driven by heat energy.
This deep ocean current is more a product
of density, or salt concentration.
Density, however, is an indirect product of
heat energy, as rainwater (due to heat energy
driving the hydrologic cycle) dilutes
saltwater.
For this reason, ocean water closer to
tropical regions is “less salty”, than ocean
water near the poles.
The denser something is, the faster it sinks.
The cold dense ocean water in the poles,
sinks along the ocean bottom in the North
Atlantic, and follows this “conveyer belt” all
the way to the Indian Ocean. Tropical waters
are less dense, and they rise, and the water
begins its trek northward along the same
path.
Surface currents are driven by winds.
These winds are also driven by
convection currents in our atmosphere!
The Trade Winds propel ocean
water westward along the
equator, and when it strikes a
continent, it is diverted
poleward. However, a narrow
return flow also occurs along the
equator. In mid-latitudes the
currents are driven eastward by
the Westerlies. The opposing
wind belts cause currents in all
the ocean basins to form gyres,
or giant loops
These currents regulate temperatures on the continents. Because global
warming is changing the density of these polar oceans because of glacial and
ice-cap melt, this current could stop. Ultimately, this could alter the
temperatures over the continents by as much as 10˚C. Global warming could
cause continental cooling in the Northern Hemisphere!
Heated air at the equator rises
up, and spreads north and south
towards the poles.
It gradually cools, sinks down in
the polar regions, and then flows
across the Earth surface to the
equator.
There it heats up again and the
convective cycle is repeated.
It isn’t an accident that the
Earth’s tropical zones are in the
warm air near the equator.
The deserts, likewise, are located
in the mid-latitude zones…and
the poles are perpetually cold.
We may think that the greenhouse
effect is bad, because ultimately it
leads to global warming.
While it is true, that greenhouse
effect is one of the mechanisms that
drives global warming, without
greenhouse effect, our Earth would
be uninhabitable! The surface of the
Earth would average about -18˚C
(0˚F).
Millions of years ago, Mars’ atmosphere
was lost, leaving it without the ability to
experience greenhouse effect. The same
thing would happen to Earth, were we to
lose our atmosphere. We may not be AS
cold as Mars, because we are much closer
to the Sun…but it would still be mighty
cold!
Think of the Earth’s envelope
of gases as being the walls of a
greenhouse.
The sun’s short wave
ultraviolet energy easily
penetrates through these
gases.
The Earth’s surface absorbs
some, and radiates some.
The Earth’s radiated energy is
transformed into infrared
thermal energy.
This long wave infrared energy
CANNOT penetrate the
Earth’s envelope of gases,
trapping the heat close to us.
The thickness
of the crust
beneath
continents is
much more
variable but
averages about
30 km; under
large mountain
ranges, like the
Alps or the
Sierra Nevada,
the base of the
crust can be as
deep as 100
km.
The crust is the outermost layer, and is rigid and very thin
compared with the other two layers.
Beneath the oceans, the crust varies little in thickness,
generally extending only to about 5 km.
The main chemical composition of the Earth’s crust is:
Like the shell
of an egg, the
Earth's crust is
brittle and can
break.
Not surprisingly, the Earth's internal structure
influences plate tectonics. The upper part of the
mantle is cooler and more rigid than the deep
mantle, and in many ways, it behaves like the
overlying crust.
This rigid portion of the mantle, together with
the outer crust, forms a rigid layer of rock called
the lithosphere.
The lithosphere has been broken up into the
moving plates that contain the world's
continents and oceans.
There are currently seven or eight major, and many minor plates. The
lithospheric plates ride on the asthenosphere. These plates move in relation to
one another at one of three types of plate boundaries: convergent boundaries,
divergent boundaries, and transform boundaries.
Earthquakes, volcanic activity, mountain-building, and oceanic trench
formation occur along these plate boundaries.
Below the crust is
the mantle, a
dense, hot layer
of non-newtonian
fluid rock,
approximately
2,900 km thick.
The mantle,
which contains
more iron,
magnesium, and
calcium than the
crust, is hotter
and denser
because
temperature and
pressure inside
the Earth
increase with
depth.
If the crust is the shell of the egg, the mantle is the eggwhite. Remember, it is the “fluid” nature of the rocks in the
mantle, which are heated through the radioactive decay of
heavy elements, that drives the convection currents that
move the tectonic plates on Earth’s crust.
Liquid
Solid
At the center of
the Earth lies the
core, which is nearly
twice as dense as
the mantle because
its composition is
metallic (iron-nickel
alloy) rather than
stony.
In keeping with the egg-analogy, unlike the yolk of an egg, however, the
Earth's core is actually made up of two distinct parts:
• a 2,200 km-thick liquid outer core and
• a 1,250 km-thick solid inner core.
As the Earth rotates, the liquid outer core spins, creating the Earth's
magnetic field. This field is important, because it protects Earth from
dangerous solar winds and cosmic rays by deflecting them away.