Introduction We will consider all spheres of Earth Lithosphere – Rock – Geology Atmosphere –...
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Transcript of Introduction We will consider all spheres of Earth Lithosphere – Rock – Geology Atmosphere –...
Introduction
We will consider all spheres of Earth
Lithosphere – Rock – GeologyAtmosphere – Air - Meteorology & ClimatologyHydrosphere – Water – OceanographyBiosphere – Life - Biology
Our goal is to understand interactions between spheres
http://www.hcsi.com/im_lib/space/geosna.jpg
First, we must agree on a method of work
Lava lamp
Scientific Method
• Hypothetico-deductive framework
• Hypotheses have testable consequences
• We test hypotheses to try to falsify them
• Karl Popper
1934 Popper Logic of Scientific Discovery
http://www.eeng.dcu.ie/~tkpw/
Falsification
• Paradigm shifts
Book: The_Structure_of_Scientific_Revolutions (1962)
biography of
An example: The earth’s orbit
• The Greek philosophers including Aristotle (384 BC - 322 BC ) observed the Sun rising in the east and setting in the west and inferred that the Sun revolved around Earth in a geocentric (Earth-centered) orbit.
http://en.wikipedia.org/wiki/Aristotle
Galileo's Letter to the Prince of Venice
http://www.mira.org/fts0/planets/099/text/txt002x.htm
Aristotle’s model is wrong
• Galileo’s observations of the orbits of Jupiter’s four largest satellites revealed that the Aristotle-Ptolemy model is unbelievable
• Objects that do not orbit the Earth
• We now know that the planets, including the Earth, orbit the Sun
http://www.hcsi.com/im_lib/imlib_space.html
IoEuropa
Callisto
Ganymede
http://www.enchantedlearning.com/subjects/astronomy/planets/jupiter/moons.shtml
A new lawA new law Isaac Newton (1665) discovered the force that
held the planets in their orbits around the sun - gravity.
gravitation, "every body in the universe attracts every other body.“
Force = mass x acceleration = maGravitational Force = gm1m2/r2 identify symbols
Both orbit, but …
Sun is much more massive, appears to hold still while the earth orbits around it.
We will see “g” again
How Far Away?
• We use the speed of light to indicate distance – light years 9460 billion kilometers
• Nearby Cepheids (variable stars) maximum brightness varies with period
• Measure apparent brightness and get distance
of far away Cepheids
• Our galaxy, the Milky Way, is 100,000 light years across (diameter)
Continuous, Emission and Absorption Spectra
White light contains a continuum of colors from short wave violet to long wave red
Hot, dense materials emit discrete "emission" spectra
When light with a continuous spectrum passes through a cold, rarefied gas, an absorption spectrum results.Each gas absorbs the same wavelengths that it emits when it is hot.
The spectrum of the light from our Sun is an Absorption spectrum.
Hydrogen
Helium
Redshift: absorption spectra shift to red with retreat of the emitter
Analogy: Passing train whistle, high to low frequency = short to long wavelength“Doppler Effect”
Very distant objects aren’t just single stars, those are galaxies of stars! Hubble: What if their colors reflect their speed and
direction?
Blue, moving toward us
Red, very distant, moving away fast
Hubble Space Telescope
The Hubble Redshift
• Hubble discovered that the most distant galaxies with Cepheids had their light
shifted to the red end of the spectrum. This meant that they are moving away from us.
• Hubble: Turn this into a new yardstick: the redder the shift, the further the galaxy
• Result: the edge of the universe (furthest objects we can detect) is approximately 15 billion light years away.
http://en.wikipedia.org/wiki/Edwin_Hubble
http://skyserver.sdss.org/astro/en/proj/advanced/hubble/conclusion.asp
Very red and far object
Origin of the UniverseThe spectral shift of light coming from distant
galaxies tells us that the universe is expanding out of a very small volume that began at most 15 billion years ago
Estimates vary according to method The universe expanded from a state of pure
energy, hydrogen atoms condensed from energy in a process called nucleosynthesis E=mc2
Origin of the Elements
• Very small volume expands “Big Bang”
• A few minutes energy cools to form H
• Hydrogen gas clouds condensed to form main sequence stars.
• H fuses to form He and heavier atoms
• “Main sequence stars” form Oxygen and Carbon.
Water = 2 Hydrogen + 1 Oxygen
H2O
Symbols for elements
Origin of Heavy Elements
• A star more than 8-20 times the mass of our sun burns faster, then expands into a red super giant star, similar to Betelgeuse.
• Pressure is high enough to also produce the heavier elements including silicon Si, magnesium Mg, iron Fe.
• Once its fuel is exhausted,
a supernova explosion occurs. http://www.solarviews.com/cap/ds/betelgeuse.htm
Main Sequence Stars
Super GiantStars
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Most rocks are made of these two
Origin of Our Solar System
• Our solar system with its abundant collection of heavier elements condensed from the gas cloud left after the explosion of a supernova.
Supernova ejects matter-rich pressure waves into space
Local concentrations of dust coalesce
Balance between gravityand solar wind
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Planetesimalsstrike growingEarth
Iron melts andbegins to sink
Lighter materialsconcentratecloser to surface
Crust andmantle
Inner core
Atmosphere
Crust
Mantle
Outer core
Liquidcore
The moon formed after a Mars-sized planet hit earth, about 4.6 bya
We got most of the core material in the exchange
DIFFERENTIATION
During coalescence:Particles assembledue to gravity – heat up
1. Rub your hands together.Motion (“kinetic”) energyis converted to heat.
Earth’s Internal Structure
• Earth’s internal layers defined by – Chemical composition– Physical properties– Deduced from Seismographs of Earthquakes– Meteorites lend support
• Layers defined by composition– Crust– Mantle– Core
Iron-Nickel Meteorite
Earth’s internal structure• Main layers of Earth are based on physical properties including mechanical strength
• Outer layers mostly Silicate Minerals: Crust and Mantle • Lithosphere (behaves like a brittle solid) Crust and uppermost mantle• Asthenosphere “weak sphere” Rest of Upper Mantle Heat softened, plastic solid • Lower Mantle Solid due High Pressures
• Inner Layers Core Iron and Nickel, outer core hotter than melting point - liquid, inner core solid due to high pressures
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CRUST
MANTLE
(least dense)
CORE(most dense)
~2900 km
~5155 km
Upper mantle
Lower mantle
Outercore
Continental crust
Oceanic crust
0 km~100 km~350 km
Lithosphere
Asthenosphere
Innercore
Conversion Factors
6370 kilometers to the center of the Earth
6370 km x 5 miles/8 km = 3981.25 miles
Earth has a radius of about 4000 miles
Note progression of densitiesOil and water
Liquid Outer Core causesMagnetic Field
Earth has a large liquid outer core, makes a magnetic field, and so a thick atmosphere
“Asthenosphere”
“Lithosphere”
The Magnetic Field protects the Atmosphere. The Atmosphere
protects Earth from most meteors
Origin of magnetic field: the liquid outer core
An Important Magnetic Field
A magnetic field once surrounded Mars. The red planet lost its protectivemagnetic field as the smaller planet cooled down more rapidly than Earth, losing its hot liquid core. Mars retains just isolated remnants of its atmosphere where pockets of relict magnetism remain.
A Perfect SpotA Perfect Spot
Earth's distance from the Sun allows Earth's distance from the Sun allows water water to exist as a to exist as a liquid. liquid.
The The biosphere biosphere of Earth has moderated the composition of of Earth has moderated the composition of the atmosphere to make it more suitable for life. Vegetation the atmosphere to make it more suitable for life. Vegetation absorbed large volumes of carbon dioxide and produced absorbed large volumes of carbon dioxide and produced oxygen Ooxygen O2 and Ozone O and Ozone O3. .
Earth's Earth's atmospheric gases atmospheric gases protect the planet from all but protect the planet from all but the largest incoming space projectiles (comets, meteorites) the largest incoming space projectiles (comets, meteorites) and ozone blocks harmful ultraviolet radiation from the Sunand ozone blocks harmful ultraviolet radiation from the Sun
The Geothermal GradientThe Geothermal Gradient The temperature gradient in the crust The temperature gradient in the crust
averages approximately 25averages approximately 25ooC per C per kilometer.kilometer.
Varies with location (higher in areas of Varies with location (higher in areas of volcanic activity) and depthvolcanic activity) and depth
Shows the interior of the planet is much Shows the interior of the planet is much hotter than the exterior. hotter than the exterior.
Volcanism an indication that heat is being Volcanism an indication that heat is being transferred from the interior toward the transferred from the interior toward the surface. surface.
Heat transfer occurs by convection, Heat transfer occurs by convection, radiation and conduction. (define)radiation and conduction. (define)
From the Asteroid Belt to Earth
• The gravitational attraction of Jupiter , or passing comets, jostles asteroids from their asteroid belt orbits causing collisions
• Sends asteroids toward the inner planets.
• Impacts with earth, moon and terrestrial planets have left scars that can still be observed today
Barrington CraterWinslow, Arizona
The Tunguska Event • Had the object responsible for the
explosion hit the Earth a few hours later, it would have exploded over Europe (most probably Scandinavia) instead of the sparsely-populated Tunguska region, producing massive loss of human life and changing the course of human history
http://en.wikipedia.org/wiki/Tunguska_event
A Dirty Comet Impact in 1908 -- No Crater
2100 km2 flattened
Comets – dirty snowballs – are jostled loose from the Oort Cloud and fall toward the Sun
K-T Mass Extinction - A Crisis in the History of Life
Cretaceous-Tertiary extinction claimed dinosaurs, flying reptiles, marine reptiles, and many marine invertebrates
Chicxulub impact structure on the Yucatan Peninsula, Mexico
65 mya this event placed dust in the atmosphere and started fires that killed 70% of all species
http://en.wikipedia.org/wiki/Chicxulub_Crater
Gravity Map
The dust is found in a thick layer worldwide, and forms the K|T boundarythe boundary between the Age of Reptiles and the Age of Mammals.
Luis and Walter Alvarez
The K\T ash layer in Alberta
Shocked Quartz
The consequences of a Chicxulub
• Powerful air blast flattens everything for thousands of square kilometers
• Massive earthquake 100 to 1000 x greater than historical times
• Deep crater 10-20 x object diameter• Massive plume of dust into atmosphere.
blocking sunlight• Lower temperatures and a short-term cooling trend. • Earth in darkness prevents photosynthesis for the next
year.• Vegetation would not survive • Colossal wildfires that would add smoke to the rapidly
darkening skies. • Giant tsunami waves with heights up to 2 miles) would be
possible from a Chicxulub-sized event in the deep ocean.
The End of the Age of Reptiles65 million Years Ago
NASA'sannualbudget fordetection ofNEOs:$3 million
One superfund cleanup $21 million
The Geology Paradigm
What is That?
Okay, that’s enough background. During WWII ships with depth sounders crisscrossed the earth’s oceans
• Alfred Wegener• Proposed hypothesis in 1915 • Published The Origin of
Continents and Oceans
• Continental drift hypothesis • Supercontinent Pangaea began breaking
apart about 200 million years ago
Continental drift: An idea
before its time
South American and African Coastlines Fit
Fossils, mountain ranges, glaciers
The revolution beginsThe revolution begins
• During the 1940s and 1950s technological advances permitted mapping of the ocean floor. Hess was captain of a minesweeper with sonar. Left it on all WWII.
• Seafloor spreading hypothesis was proposed by Harry Hess in the early 1960s.
http://www.amnh.org/education/resources/rfl/web/essaybooks/earth/p_hess.html
Remember Arthur Holmes
Harry Hess
http://www.gfdl.noaa.gov/~io/Bubble.html
Convection, the basic idea of Plate Tectonics, Atmospheric Cells, and Ocean Currents
Bubble Convection ( i.e. the lava lamp model)
Start with a hot bubble, it expands and so is less dense. It rises as surrounding dense material presses on it, especially at deeper, higher pressure, levels. When it hits a barrier it spreads, cools and becomes denser. It sinks and returns material to the start.
1_20
Mid-oceanridge
Harry’s Idea:Sea-Floor Spreading
Convection cells in the hot mantle hit the lithosphere barrier. They spread out and cool,
pulling the lithosphere apart. New lava gets into the cracks, filling the gap, and FORMING NEW
OCEAN CRUST!
Some mineral crystals in solidifying lava align with Earth’s magnetic field. Tilt tells latitude.
Earth’s North –SouthPoles can flip. Tilt will change direction
New lava rock will have the signature of the magnetic field when it froze
How Can We Test Harry’s Hypothesis?
Paleomagnetic reversals would be recorded by lava (called basalt) at mid-ocean ridges
Fred Vine and Drummond Matthews: Harry’s idea is A TESTABLE HYPOTHESIS
New lava rock will have the signature of the magnetic
field when it froze
Maps of Magnetic Stripes in Oceanic CrustPrinceton PostDoc Fred Vine
and Drummond Matthews
Did they prove Harry’s idea?
Plate tectonics: The new paradigmPlate tectonics: The new paradigm• More encompassing theory than
Wegener’s continental drift
• Explains motion of Earth’s lithosphere by seafloor spreading (creation of new ocean floor) and subduction (destruction of old ocean floor)
• All major earth features are explained
Harry Hess’s Seafloor Spreading developed into
Here we see Divergent Margins (the Atlantic Mid-Ocean Ridge – Harry’s Sea-Floor Spreading) and
Convergent Margins (the dense Pacific Ocean Plate is being dragged under South America – called subduction zones )
The Asthenosphere boils, like soup. This moves the cold Lithosphere PLATES above
Lithosphere is "the scum floating on top of the boiling soup"
Continental Lithosphere
Oceanic Lithosphere
Subduction Zone
Asthenosphere
Divergent Boundaries (Rising Convection Currents) Mid-Ocean Ridge
Convergent Boundaries (Descending Convection Currents)
Subduction Zone
Mantle material rises, ponds under the lithosphere, spreads, pulls the lithosphere apart. Mantle minerals exposed to low pressures. Some mantle minerals are unstable at low pressures.They melt, forming lavas, which get into the cracks, and cool into basalt, the main rock of ocean lithosphere.
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NORTHAMERICANPLATE
CARIBBEANPLATE
PACIFICPLATE
COCOSPLATE
ANTARCTIC PLATEANTARCTIC PLATE
Mid-AtlanticRidge
Mid-AtlanticRidge
SOUTHAMERICANPLATE
AFRICANPLATE
ARABIANPLATE
INDIAN-AUSTRALIANPLATE
PHILIPPINEPLATE
PACIFICPLATE
FIJIPLATE
EURASIANPLATE
NAZCAPLATE
SCOTIAPLATE
90º90º 0º
0º
45º
45º
180º
0º
45º
45º
180º 180º90º 90º0º
180º
JUAN DEFUCAPLATE
Convergent plateboundaryDivergent plateboundary
Transform plateboundary
Seven or so major plates, about an equal number of small plates
Components of Plate Tectonics: there are three main types of plate marginsDivergent, Convergent and Transform
Each plate bounded by combination of all three boundary types
Divergent boundaries are located mainly along Mid-Ocean Ridges (MORs)
The East African Rift
MORs can start as rift valleys, the dry land precursor of mid-ocean ridges.
Soon enough they connect to the sea, and flood, forming a new ocean
CONTINENTAL PLATE
CONTINENTAL PLATE
Oceanic lithospherebeing subducted
(a)
Convergent Plate BoundariesIf Seafloor Spreading (Divergence) is occurring somewhere,
plates must push against one another in other areas
Subducted Ocean Plate loses water and adjacent Mantle partially melts, new buoyant magma rises to the surface, forming a
Volcanic Arc such as the Andes Mountains of South America
Rocks deformed in collision
Collisionalmountains
(b)
Collisions formed the Appalachians, and, more recently, the Himalayas and the Alps.
Suture
Once the ocean crust between them is subducted, the continents collide. Both are thick and made of buoyant (low density) minerals, so neither
continent can be subducted under the other
The collision of India and Asia produced the Himalayas
1. Subduction Zone Phase 2. Collision Phase
Convergent Boundaries
Ocean-Continent
Ocean-Ocean
Continent-Continent
TypesProducts
India
Asia
Andes, Cascades
Japan, Aleutians
Himalayas, Alps, Appalachians
Favorite quiz picture
Transform Margins accommodate movement as plates slide past one another, for example
the San Andreas Fault and between Mid-Ocean Ridge segments
Transform Plate
Boundaries
Plate Tectonics Explains It AllPlate Tectonics Explains It All• The Plate Tectonic concept caused the
realization that Earth’s many geologic features were all caused by the same process.
• We now understand mountains, volcanoes, and big earthquakes associated with, for example, the San Andreas fault.
• We understand rift valleys and how oceans form, deep ocean trenches, mid-ocean ridges, and why fossils and mountain ranges look alike across vast oceans.