EAS 100 A2 02 Cycles Handouts-2
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Transcript of EAS 100 A2 02 Cycles Handouts-2
15-09-04
1
Introduction to Earth Science: Studying the Earth • Scientific methods • Earth scientists:
areas of study within the Earth sciences
• Systems and cycles in Earth science
• Applications of Earth and Atmospheric Science
Read: Blue Planet: Ch. 1 The Earth System
Scientific methods and the study of the Earth
Source: USGS
Experiment and observation
• Physics and chemistry are primarily experimental sciences
• Earth Science is
primarily an observational science (though experiments are also used)
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Observation in the age of satellites
https://svs.gsfc.nasa.gov/vis/a000000/a003800/a003868/GlobalSnowNDVIFire.mp4
Earth Science in the age of computers
https://svs.gsfc.nasa.gov/vis/a010000/a011700/a011719/11719-1920-MASTER.mp4
What makes an idea scientific?
• It can be tested against observation or experiment
BP 12.18
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What makes an idea scientific?
• It can be tested against observation or experiment
BP 12.18
The Scientific Method
A long, careful series of experiments or observations that aims to explain or understand the natural world.
Observation and hypotheses
Step 1: Observation
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The Scientific Method
Step 2: Hypothesis formation
hypothesis:
A tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation.
Step 3: Hypothesis testing
The Scientific Method
The Scientific Method
Step 3: Hypothesis testing
And steps 4, 5, 6, etc.
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The Scientific Method
Step 3: Hypothesis testing
And steps 4, 5, 6, etc.
If a hypothesis passes the tests…
Source: www.destination360.com
The Scientific Method
Hypothesis becomes theory
theory:
A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.
The Scientific Method • If, over many years
and much additional testing, the theory holds…
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The Scientific Method
Theory becomes law
law:
A statement describing a relationship observed to be invariable between or among phenomena for all cases in which the specified conditions are met
• Example: “Law of Conservation of Energy” (1st Law of Thermodynamics)
In a system of constant mass, the energy involved in physical or chemical change is neither created not destroyed but merely converted from one form to another
The Scientific Method
• Example: “Law of Conservation of Energy” (1st Law of Thermodynamics)
In a system of constant mass, the energy involved in physical or chemical change is neither created not destroyed but merely converted from one form to another
The Scientific Method
E = mc2
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The Scientific Method
Repeated testing, evaluation, modification of hypothesis, more testing…
Very powerful methodology!
• An example: principle of superposition
Sandstone layers in Nova Scotia
Principles: generalizations with exceptions
Principles: generalizations with exceptions • An exception:
overturned strata in mountain belts
Folded sedimentary layers in the Swiss Alps
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The principle of uniformitarianism
• Ancient sand dune, Zion, Utah
The principle of uniformitarianism
• Ancient sand dune, Zion, Utah
• Modern sand dune, Yuma, Arizona
The principle of uniformitarianism
• Ancient sand dune, Zion, Utah
• Modern sand dune, Yuma, Arizona
Are the processes that created ancient features similar to those that create modern ones?
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The principle of uniformitarianism
• Proposed by James Hutton in 1795 – Theory of the Earth
• Ancient features of the Earth are best interpreted in terms of processes that operate at the present day
• ‘The present is the key to the past’
Siccar Point, Berkwickshire, Scotland
‘Hutton’s unconformity’
• Hutton interpreted the contact between the lower rocks and the upper rocks as an ancient erosion surface, produced by processes similar to those operating at the present day
BP 1.12
Changes in Earth History
• Hutton proposed a very strict principle of uniformitarianism
• We now recognize that there have been big changes in Earth processes including:
long term changes (e.g. tectonics; evolution of the atmosphere)
short term changes (catastrophic meteorite impacts)
Source: exploratorium.com
Meteor Crater, Arizona
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Principle of actualism
• A more moderate version of Hutton’s principle is called actualism
‘The natural (i.e., physical and chemical) laws that allowed the formation of ancient features of the Earth are the same ones in operation today.’
• This allows for change!
Relationship to other sciences:
Source: USGS
• Earth science is largely an observational science
Relationship to other sciences: • Earth science makes use of principles and laws derived
from other sciences, such as physics, chemistry and biology. – Example: “Law of Conservation of Energy”
(e.g., 1st Law of Thermodynamics)
In a system of constant mass, the energy involved in physical or chemical change is neither created not destroyed but merely converted from one form to another
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Earth scientists: areas of study within the Earth sciences
Source: NASA
Geologists
• Field observations • Geologic maps • Samples • Chemical analyses • Resource
development and extraction
Shiprock Peak, New Mexico
Source: University of Wisconsin-Madison
Geophysicists
• Use variations in the Earth’s physical properties to determine subsurface structure, composition, etc.
Seismic velocities
Magnetic, electrical properties
Variations in strength of local gravitational field
• Examine the earth using natural phenomena such as earthquakes
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Paleontologists and Biogeographers
• Paleontologists Fossils and the history of life
• Biogeographers Distribution of living things at the present day
Hydrologists & Oceanographers
• Liquid water on and below the Earth’s surface
• Living things in
water • Sediments
deposited on the sea floor or the bottom of lakes
Atmospheric Scientists
• Meteorologists & climatologists
• Physics of the atmosphere
• Short term changes in the atmosphere (weather)
• Geographical variation and long term changes in the atmosphere (climate)
Source: University of Washington
Hurricane Katrina
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Glaciologists
• Behaviour and distribution of ice
• The impact of glaciers
on the landscape (e.g., erosion, deposition) and downstream environments
• Interactions between
ice masses and climate
Canine Glacio-hydrologists
Donjek
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Logan
Logan
Systems and cycles
A system is a portion of the universe that can be separated from the rest for the purpose of observing changes
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Types of systems
• Systems may be:
– Isolated – Closed – Open
BP 1.3
Isolated systems
• No matter or energy lost or gained
• Imaginary concept
BP 1.2
Closed systems
• No matter lost or gained; energy may be exchanged with surroundings
• The Earth is approximately a closed system
BP 1.2
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Open systems
• Matter and energy exchanged with surroundings
• Examples of open systems: – An ocean – An island – A forest – A leaf – You
BP 1.2
The Earth as a system
• Earth is approximately a closed system
• Note: – Small amounts of
gas are lost to space
– Small amounts of material are added by meteorites and comets
– These amounts are extremely small compared with the mass of the Earth
BP 1.5
Systems within the Earth
• The Earth system contains several major open systems – Atmosphere – Geosphere – Hydrosphere – Biosphere – Cryosphere
BP 1.5
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Cycles
• Cycles trace the flow of material or energy through systems
• Examples include: – The energy cycle – The hydrologic cycle – The rock cycle
• When a cycle is quantified it is sometimes called a ‘budget’
www.savingadvice.com/images/blog/hello-kitty-bicycle.jpg
The Energy Cycle Source: http://www.noaanews.noaa.gov
The Sun
Sun’s energy output
• 3.8 x 1026 W total energy output
• 1.7 x 1017 W reaches Earth
• Energy flux at Earth’s distance is 1370 W per m2
BP 3.4
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Energy flux on Earth’s surface
Earth Radius: R=6370 km
Energy flux: 1370 W/m2
Earth intercepts πR2=1.74x1017 W
Spread out over sphere, which has area 4πR2
Average energy flux is thus 1370 [W/m2]/4 = 342 W/m2
BP 3.5
Energy budgets • Energy flow is measured in Watts per square meter • 1 W = 1 J/s • First law of thermodynamics: conservation of energy
Source: http://stephenschneider.stanford.edu
The Energy Cycle
• Drives all of the processes that we see operating on the Earth
• Energy inputs – Solar radiation: light, radiant heat,
etc., – Geothermal energy: released
from nuclear breakdown of Uranium, Thorium etc.,
– Tidal energy – a result of gravitational attraction of Moon
• Energy losses – Reflection into space – Re-radiation, as radiant heat
Tides
Geothermal energy
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Solar energy
• Energy comes from the sun as electromagnetic (or EM) radiation, mainly in the visible and infrared bands.
• About 1.74 x 1017 W (Watts) or 174,000 TW (Terawatts)
Short wavelength Solar radiation 174,000 TW
Where does solar energy go? (1)
• About 30% is reflected into space (52,000 TW) • Just under half is converted to heat and is re-
radiated (81,000 TW)
Short wavelength Solar radiation 174,000 TW
Long wavelength radiation Reflected
into space 52,000 TW
Converted to heat 81,000 TW
Where does solar energy go? (2)
• Just under a quarter goes into melting ice and evaporating water; energy is stored in the hydrosphere (40,000 TW)
• 350 TW are converted to winds, ocean currents, waves etc
Short wavelength Solar radiation 174,000 TW
Long wavelength radiation Reflected
into space 52,000 TW
Converted to heat 81,000 TW
Evaporation and melting 40,000 TW
Precipitation
Wind, Waves and currents
Water and ice storage bank
350 TW
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Where does solar energy go? (3)
• 40 TW are captured by living things
Short wavelength Solar radiation 174,000 TW
Long wavelength radiation Reflected
into space 52,000 TW
Converted to heat 81,000 TW
Evaporation and melting 40,000 TW
Precipitation
Wind, Waves and currents
Water and ice storage bank
350 TW
Photo-synthesis
40 TW Plant
storage bank
Decay
Buried organic matter
Geothermal energy
• Energy is released within the Earth by the slow breakdown of Uranium, Thorium and other radioactive elements.
• Total amount is estimated at ~32 TW
Short wavelength Solar radiation 174,000 TW
Long wavelength radiation Reflected
into space 52,000 TW
Converted to heat 81,000 TW
Evaporation and melting 40,000 TW
Precipitation
Wind, Waves and currents
Water and ice storage bank
350 TW
Photo-synthesis
40 TW Plant
storage bank
Decay
Buried organic matter
Geothermal energy 32 TW
Where does geothermal energy go?
• This energy drives volcanoes, hot springs, earthquakes, and movements of continents.
• It is also radiated in very small amounts, averaging ~60 mW/m2, from the Earth’s surface
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Where does geothermal energy go?
– Volcanoes and hot springs on land 0.3 TW – Volcanoes under the sea 11 TW – Heat loss (conduction) from the surface 21 TW
Short wavelength Solar radiation 174,000 TW
Long wavelength radiation Reflected
into space 52,000 TW
Converted to heat 81,000 TW
Evaporation and melting 40,000 TW
Precipitation
Wind, Waves and currents
Water and ice storage bank
350 TW
Photo-synthesis
40 TW Plant
storage bank
Decay
Buried organic matter
Geothermal energy 32 TW
Volcanoes Hot springs 0.3 TW Heat flow 21 TW
Submarine volcanoes 11 TW
Where does tidal energy go?
• Tidal energy: 27 TW
Short wavelength Solar radiation 174,000 TW
Long wavelength radiation Reflected
into space 52,000 TW
Converted to heat 81,000 TW
Evaporation and melting 40,000 TW
Precipitation
Wind, Waves and currents
Water and ice storage bank
350 TW
Photo-synthesis
40 TW Plant
storage bank
Decay
Buried organic matter
Geothermal energy 32 TW
Volcanoes Hot springs 0.3 TW Heat flow 21 TW
Submarine volcanoes 11 TW
Tides 27 TW
Summary of energy cycle
Short wavelength Solar radiation 174,000 TW
Long wavelength radiation Reflected
into space 52,000 TW
Converted to heat 81,000 TW
Evaporation and melting 40,000 TW
Precipitation
Wind, Waves and currents
Water and ice storage bank
350 TW
Photo-synthesis
40 TW Plant
storage bank
Decay
Buried organic matter
Geothermal energy 32 TW
Volcanoes Hot springs 0.3 TW Heat flow 21 TW
Submarine volcanoes 11 TW
Tides 27 TW
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Solar energy budget
Source: http://stephenschneider.stanford.edu
Laws of thermodynamics • Energy is conserved (1st Law of Thermodynamics)
• All energy flows are ultimately converted to heat. This reflects the 2nd Law of Thermodynamics:
– Whenever energy is used to do mechanical work in a system, some of that energy is dispersed (lost) as heat.
– Because heat is an unorganized, random vibration of molecules, we say that the entropy (a measure of disorganization) of the system has increased.
– The net entropy of the universe always increases.
2nd Law of Thermodynamics • Without some external source of energy, entropy on
Earth would increase until we use up all available energy (losing it as heat).
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2nd Law of Thermodynamics • Without some external source of energy, entropy on
Earth would increase until we use up all available energy (losing it as heat).
Source: http://www.geocities.com/larkspur10/neo/228/towers.jpg
Source: http://www.noaanews.noaa.gov
The Sun
2nd Law of Thermodynamics
The Hydrologic Cycle • Water cycle BP 1.9
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Hydrologic pathways: Evapotranspiration
• Evaporation – from
surface water
– from land • Transpiration
– from plants
BP 1.9
Hydrologic pathways: Condensation and precipitation
• Condensation – Clouds
• Precipitation – Rain – Snow
BP 1.9
Hydrologic pathways: Surface and subsurface flow
• Melting • Surface flow
– Glaciers – Streams – Rivers
• Infiltration • Groundwater
movement
BP 1.9
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Hydrologic reservoirs
• Oceans (97.5%)
• Ice sheets (1.85%)
• Groundwater (0.64%)
• Lakes, rivers, atmosphere (.01%)
BP 1.9
Earth’s water budget
1015 = 1,000,000,000,000,000
Earth’s water budget
1015 = 1,000,000,000,000,000 (a “million billion”)
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Reservoir change
• For most of these reservoirs, the rate of flow in approximately balances rate of flow out.
• Volume of water in the reservoir is approximately constant
• When flow in > flow out, reservoir expands • When flow in < flow out, reservoir contracts • The ice sheet reservoir has been getting smaller over
time because melting > snowfall
Residence time
• Size of reservoir / flow rate = residence time • A measure of the average time that a water molecule
spends in the reservoir • Typical residence times:
Oceans and ice caps: thousands of years Streams and rivers: a few weeks Atmosphere: a few days
Hydrologic cycle BP 1.9
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The Rock Cycle • Cycling of rock material at
surface of the Earth • Three types of rock
Igneous Sedimentary Metamorphic
BP 1.12
Magma • Melting point: 800-1200ºC
(depending on rock type) • Molten rock is magma; at the
surface, it’s called lava
BP 7.5
Igneous rock
• Cooling • Solidification
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Intrusive Rocks
• Magma cools below surface
• Generally have larger crystals
• “Phaneritic” (visibly crystalline)
Ansel Adams
Extrusive Rocks
• Lava that cools above surface
• Typically have microscopic crystals
• “Aphanitic” (without visible crystals)
Source: USGS
Differences in Crystal Size
• Intrusive rocks “phaneritic” large crystals
• Extrusive rocks “aphanitic” small crystals
Due to differences in rate of cooling
Slow = large Fast = small
http://www.birdseyefoods.com
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Weathering Destructive processes that change the physical and chemical characteristics of rocks at the earth's surface.
Erosion Transportation of weathering products
Source: http://www.truecolorearth.com
Sediment Deposition à Sediment Source: http://en.wikipedia.org/wiki/McCormick's_Creek_State_Park
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Sedimentary rock Results from “lithification” of sediments Sedimentary Rock: Often “Clastic” (made up of fragments)
Source: http://library.thinkquest.org/05aug/00461/images/sandstone.jpg
Metamorphism • Results from heat and pressure (without melting)
BP 4.22
Metamorphic rocks
• New minerals • Change in texture • Fabric
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Igneous rock
• For comparison…
Metamorphic rocks
• New minerals • Change in texture • Fabric
The rock cycle: summary
Magma
Igneous rock
Weathering
Transportation
SedimentLithification
Sedimentary rock
Metamorphism
Metamorphic rockMelting
Erosion
Deposition
Cooling
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Other Cycles
• Biogeochemical cycles
– Nitrogen cycle – Carbon cycle
(We’ll look at these later on.)