Earth's Energy Reservoirs and Cycles

The Earth System
The Blue Planet: Chapter 1

Outline
• Earth System Science
• Systems
• Earth System Reservoirs
• Dynamic Interactions Among
Reservoirs
• How Science Works

Earth System Science
• Earth system science is the new
holisitic approach to studying the Earth
as a whole system of many interacting
parts
– The ocean -Soils
– The atmosphere -Plants
– The continents -Animals
– Lakes and rivers

Earth System Science
• Requires observations of Earth at
various scales
• The quintessential tool for making these
observations is remote sensing with
satellites
• Geographic Information Systems
provide ways for scientists to store and
analyze vast amounts of data

Systems
• A system is any portion of the universe
that can be isolated from the rest for the
purpose of observing and measuring
changes
• By observing and measuring changes,
systems can be used to study complex
problems

Systems
• A model is a representation of
something, typically a simplification of a
complex original
• We can build models of processes,
which can represent some of Earth’s
systems

Systems
• A box model is a simple graphical
representation of a system
• It can show essential features
– The processes and rates by which matter
or energy enters and leaves the system
– The processes and rates by which matter
or energy moves within the system
– The amount of matter or energy in the
system and its distribution

Systems
• A key to understanding the Earth
system is to measure how volumes and
exchanges of materials and energy
between Earth’s reservoirs change over
time
• The challenge is to determine why the
changes happen, and how quickly

Systems
• The amount and of energy or matter that is
transferred is called flux
• The places where energy or matter is stored are
called reservoirs
– If the flux into a reservoir is greater than the flux out,
that reservoir is a sink
– If the flux into a reservoir is less than the flux out, that
reservoir is a source
• The length of time energy or matter spends in a
reservoir is its residence time, when this time is
so great that matter is isolated for very long
periods, it is called sequestration

Systems
• Earth comprises four vast reservoirs
with constant flows of energy and
matter among them
– The atmosphere
– The hydrosphere
– The biosphere
– The geosphere
• As a whole, Earth is essentially a closed
system

Systems
• Two important implications of Earth
being a closed system are
1. The amount of matter in a closed system
is fixed and finite
2. If changes are made in one part of a
closed system, the results of those
changes eventually will affect other parts
of the system

Earth System Reservoirs
• The place where Earth’s four reservoirs
interact most intensively is a narrow
zone called the life zone
• Conditions favorable for life are created
by interactions between the lithosphere,
hydrosphere and atmosphere, and
modified by the biosphere

• The Geosphere
– Is the solid earth
– Composed mainly of rock and regolith
– Where energy that comes into the Earth
system from outside sources meets energy
that comes from within the planet
– Energy sources combine and compete to
build up and wear down the materials of
Earth’s surface

• The Hydrosphere
– The totality of Earth’s water
– Includes oceans, lakes, streams,
underground water, and all snow and ice
– The perennially frozen parts of the
hydrosphere are collectively the cryosphere
– The hydrosphere and the atmosphere store,
purify, and continually redistribute water

• The Atmosphere
– The mixture of gases that surrounds Earth
– Predominantly Ni, O2, Ar, CO2, and H2O
– In the context of the planet it is a very very
thin layer, but it protects life from damaging
solar radiation, is the reservoir for oxygen
and carbon dioxide
– It is the outer boundary of the Earth system

• The Biosphere
– Includes all of Earth’s organisms and
matter that has not yet decomposed
– The biosphere greatly affects every other
of Earth’s systems
• Photosynthesis
• Oxygen as a highly reactive gas

• The Anthroposphere
– The “human sphere”
– Comprises people, their interests, and their
impacts on the Earth system
– The part of the natural system that has
been modified by humans
– Includes the technosphere, specifically to
technology, machines, and the built
environment

Dynamic Interactions Among
Reservoirs
• Because energy flows freely into and out
of systems, all systems respond to inputs
and, as a result, have outputs
• A special kind of response, feedback,
occurs when the output of the system also
serves as an input
– Negative feedback: the system’s response is
in the opposite direction of initial input
• Often self-limiting or self-regulating

Reservoirs
• Positive feedback: an increase in output
leads to a further increase in output
– Vicious cycle
– Destabilizing

Reservoirs

Reservoirs
• The constant movement of material
from one reservoir to another is called a
cycle
• Natural cycles are not simple, and exist
in a state of dynamic equilibrium
• There are many important Earth cycles

Reservoirs
• The Hydrologic Cycle
• The Energy Cycle
• The Rock Cycle
• The Tectonic Cycle
• Biogeochemical Cycles

Reservoirs
• Humans involve or affect natural cycles
• Significant changes are now taking
place in many Earth reservoirs, as a
result, many are changing in
unexpected ways
• Scientists have coined a term to
describe changes produced in the Earth
system as a result of human activities:
global change

How Science Works
• Earth system science, like all other
forms of science, advances by
application of the scientific method
• The scientific method is based on
observations and the systematic
collection of evidence that can be seen
and tested by anyone with resources

How Science Works
• Scientists start with an observation and seek to
acquire evidence about it through measurement
and experimentation
• Scientists try to explain their observations by
developing a hypothesis
• Once a hypothesis has been examined and found
to make successful predictions and withstand
numerous tests, it may become a theory
• Eventually, a theory or group of theories whose
applicability has been decisively demonstrated,
may become a law or a principle

How Science Works
• The fact that nothing is absolutely
certain in nature is not problematic for
scientists, but can be difficult for non-
scientists to comprehend fully
• It is important to understand that
uncertainty does not imply a lack of
scientific knowledge or understanding

Energy
The Blue Planet: Chapter 2

Outline
• What is Energy?
• External Energy Sources
• Internal Energy Sources
• Earth’s Energy Cycle
• Energy and Society

What is Energy?
• Energy is the capacity to
– Do work
– Move matter
– Make things happen
• Energy exists in many different forms
• The sum of the different kinds of energy
in a system is the internal energy

What is Energy?
• To change the internal energy of a
system, energy must be added or taken
away
• This is called work

What is Energy?
• Energy can take lots of different forms,
but all are described as either
• Potential Energy
– Energy that is stored in a system
• Kinetic Energy
– Enegy that is expressed in movement
• Or a combination of these

What is Energy?
• Potential energy, energy that is stored
in a system, can take the form of
– Chemical energy
– Nuclear energy
– Stored mechanical energy
– Gravitational energy

What is Energy?
• Kinetic energy, energy that is expressed
in the movement of electrons, atoms,
molecules, materials, and objects,
includes
– Radiant energy
– Electrical energy
– Thermal energy (heat)
– Sound
– Motion

What is Energy?
• The transfer of energy from one form to
another and one body to another is
subject to the 3 laws of
thermodynamics
– 1st
Law: Conservation and Transformation
– 2nd
Law: Efficiency and Entropy
– 3rd
Law: Absolute Zero

What is Energy?
• 1st
Law: Conservation and Transformation
– In a system of constant mass, the energy
involved in any physical or chemical change
is neither created nor destroyed, but merely
changed from one form to another.

What is Energy?
• 2nd
Law: Efficiency and Entropy
– Energy always changes from a more
useful, more concentrated form to a less
useful, less concentrated form.

What is Energy?
• 3rd
Law: Absolute Zero
– The third law of thermodynamics
postulates the existence of the state of
absolute zero temperature
– Temperature is a measure of heat, the
vibrational motion of particles
– In a state of absolute zero temperature, all
of this motion would cease
– Absolute zero provides the foundation
point for the Kelvin temperature scale

External Energy Sources
• All processes in the Earth system are
driven by energy
• External energy sources are
– The sun
– Gravity and tides

• The Sun is a star that radiates heat as a
result of thermonuclear reactions
(fusion) in its core
• Fusion converts matter to energy
• Energy released by fusion in the Sun is
in the form of gamma rays (98%) and
neutrinos
• Gamma rays are responsible for the
tiny fraction of the Sun’s energy that
reaches the Earth

• The Sun consists of six
concentric layers
– The Core: site of all nuclear
fusion reactions, 62% He,
38% H
– The Radiative Layer: energy
released from the core
moves across by radiation
– The Convective Layer:
across which energy moves
by convection

• The Sun consists of six
concentric layers
– The Photosphere: the
visible portion of the sun
that emits light
– The Chromosphere: a
low-density layer of very
hot gas
– The Corona: the
outermost layer of even
lower density gas

• Radiation energy released in the Sun’s
core has a very short wavelength and is
extremely energetic
• As gamma rays move outward from the
core they are repeatedly absorbed and
reemitted as longer-wavelength, lower-
energy radiation

• The energy flux from the Sun varies
with wavelength, and the shape of the
Sun’s spectral curve matches that of a
blackbody radiator
• This refers to the radiation-absorbing
properties of a body, a perfect
blackbody absorbs all light that strikes it

• The spectrum of electromagnetic radiation
emitted by the Sun is not the same as the
spectrum of solar radiation that reaches the
Earth’s surface
• Gases in the Earth’s atmosphere selectively
absorb some wavelengths of solar radiation
• The ozone layer absorbs very short
wavelength (UV) radiation, this energy is
transformed into heat, warming the
stratosphere

• The Sun is responsible for 99.985% of all
energy in the Earth system, but external
energy also comes in as a result of gravity:
the mutual physical attraction between the
Earth and the Moon
• The gravitational pull that the Moon exerts
on Earth is balanced by an equal and
opposite inertial force created by Earth’s
movement

• The side of Earth nearest the Moon is
pulled toward the Moon by gravity while
the side of Earth farthest from the Moon
is pulled away by inertial force
• This produces a periodic distortion
called a tide, which takes the form of a
flattening distortion (ellipsoid)

• The Earth is elastic, meaning it has the
capacity to deform reversibly
• The internal resistance (friction) caused
by the elastic deformation within the
planet is translated into heat - one of
Earth’s internal heat energy sources
• Though both are caused by gravity, do
not confuse Earth tides (body tides) with
ocean tides!

Internal Energy Sources
• In addition to energy from the Sun and
Earth tides, there are sources of energy
that come from within the planet itself
• Terrestrial (geothermal) energy sources
have a much smaller input than the sun,
but greater than the tidal contribution

• The increase in temperature as
you go deeper in the Earth is
called the geothermal gradient
• The geothermal gradient varies
from place to place and becomes
less pronounced with depth
• By extrapolation, the temperature
of the Earth’s core is calculated
to be about 5300 K - almost as
hot as the surface of the Sun!

• Heat energy flows out through solid rocks at
Earth’s surface by conduction
• However, volcanoes involve the movement of hot
material from inside the planet to outside, so
some heat energy reaches the Earth’s surface by
convection
• Convection is a very efficient way for the Earth to
transfer heat from its interior to the surface, and
convective heat transfer provides the driving force
behind plate tectonics

• There are several sources for Earth’s
internal terrestrial energy
– Radiogenic heat: the main source,
accounting for ~66% of interior heat flow, is
produced by decay of radioactive elements
– Accretionary heat: internal heat left over
from the formation of the Earth by
countless particles colliding into each other
and sticking together

• There are several sources for Earth’s
internal terrestrial energy
– Tidal heating: heat generated by internal
friction from the constant distortion of the
planet
– Core formation: heat from the gravitational
potential energy of the dense core material
sinking into the center of the planet plus
heat released as the innermost material
solidified

Earth’s Energy Cycle
• The energy cycle encompasses the
inputs and outputs, pathways, and
reservoirs for the energy that drives all
of the other cycles of the Earth system
• Functioning like a budget, energy may
be added or subtracted and transferred
from one reservoir to another, but
overall the transactions must balance

• Energy In
– Incoming solar radiation powers the winds,
rainfall, ocean currents, waves, the rest of
the hydrologic cycle, and photosynthesis
– Earth’s internal heat energy drives the
tectonic cycle, causing the lithospheric
plates to shift, uplift mountains, cause
earthquakes and cause volcanic eruptions

• Energy Out
– Earth loses energy by reflection (albedo)
and by degradation and reradiation
– 40% of solar radiation is reflected by the
top of the atmosphere, clouds, ocean
surfaces, continents, and ice and snow

• Energy Out
– Absorbed solar radiation undergoes
irreversible degradation through transfer
from reservoir to another and conversion
from one form to another, eventually
ending up as heat, reradiated into space
– Earth’s outgoing radiation is also
selectively absorbed by gases in the
atmosphere, causing the greenhouse
effect

Energy and Society
• Humans tap into energy from Earth’s
reservoirs to extract power for
– Transportation
– Home and office use
– Industrial use
• Energy consumed by the global
population annually is 3.0 x 1020
Joules
– Equivalent to burning 10 barrels of oil per
person per year

Energy and Society
• 4 energy sources have
been extensively
developed:
– Fossil fuels
– Biomass energy
– Hydroelectric energy
– Nuclear energy
• 5 other sources are
being developed
more extensively:
– Solar energy
– Wind energy
– Waves
– Tides
– Geothermal energy

Earth's Energy Reservoirs and Cycles

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