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chap1_highlights - Cosmology and the Birth of the Earth and...

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Unformatted text preview: Cosmology and the Birth of the Earth and Journey to the Center of the Earth Chapter 1 Highlights History of Concepts ~1000 BC ~ days of Homer -Earth is a flat disk with water at edges + land in middle. Stars overhead in Celestial Sphere + Hades below The Flat Earth Society http://www.flat-earth.org/ Heraclides (330 B.C.) formalized Plato's first Solar System model, called the geocentric model. http://zebu.uoregon.edu/~js/ast121/lectures/lec01.html Claudius Ptolemy, (87 -150 AD), astronomer, mathematician and geographer from Alexandria, Egypt, believed geocentric universe and circular orbits but had to explain retrograde motion Digitally stacked images showing location of Mars on successive nights in August 2004 showing http://campus.pc.edu/faculty/rarts/courses/physics/105/notes/Topic_2_The_Motions_of_the_Planets/Ptolemys_geocentric_universe.jpg Retrograde Motion circa 1500’s…Copernicus’s revolution… the Heliocentric view of the Universe… Do galaxies move in relation to each other? Need to understand noise (sound and light) has a pitch Pitch depends on frequency - # of waves moving past a point in given time Light also is measured by its frequency Louie Joe Doppler Effect When train stands still, Louie and Joe hear the same pitched whistle. When train moves towards Louie, its motion squeezes the sound waves reaching Louie, and stretches those reaching Joe. Louie Louie Our ears interpret squeezed and stretched waves as sounds of different pitch. For Louie, the moving whistle sounds higher than when it was standing still; for Joe, it sounds lower. Joe Back to light frequency Low frequency High frequency Doppler effect can be applied to light to see the effect of a star’s velocity as seen from Earth. W. W. Norton American astronomer Edwin Hubble in 1929 Hubble absorption lines outside our galaxy are shifted towards RED shifted ‘Red shift’ = source is moving away from Red Earth at very high velocity Earth wherever he looked, he saw only red shift wherever only Conclusion: each galaxy is moving each away from its neighbors, i.e., the i.e., Universe is expanding Universe Origin of the Universe Evidence indicates that all matter was concentrated in a single point; unimaginable energy kept matter from organizing into elements Fig. 1.15 Something triggered the Big Bang ~13.7 billion yrs ago Something Big NASA Within 1 second, Universe expanded & cooled enough Within to allow protons and neutrons and H to form to After 3 minutes of cooling, H, He and Li formed. After further cooling early elements began collecting into clouds called NEBULA Some nebula assembled larger + larger clouds due to gravitational attraction; others were left behind in isolation Gravity causes largest nebular cores to become very dense; H and He collide & FUSE forming more complex elements, up to Fe (#26 of 92 naturally occurring elements) Enormous energy is released in these nuclear fusion reactions, and a STAR is born When the H & He fuel is used up, the star enters the SUPERNOVA stage Supernovae explode and scatter mass into space, forming all of the remaining 92 elements in the process Nebular hypothesis: formation of our solar system A 2nd- or 3rd-generation nebula formed from H, He, + heavier elements produced by fusion reactions in stars and during explosions of supernovae. 80% H, 15% He, 5% other elements http://meteorites.lpl.arizona.edu/nebula.html The nebula condensed into a swirling disc called an accretionary disk Separation of the Sun and planets The center grew dense + hot for fusion to begin and become our Sun. Solid dust particles condensed into rings that orbited the Sun. ~4.6 byrs ago (oldest meteorites & Moon rocks) Dust particles collided, stuck together, and assembled into planetesimals. Formation of the Earth Planetesimals grew by continuous collisions. Gradually, an irregularly shaped proto-Earth developed. The interior heated up and became soft and gravity reshaped the proto-Earth into a sphere. The interior of the Earth separated into a core and mantle. Homogeneous Earth Homogeneous Formed from multiple Formed impacts of material left over from Big Bang, fusion reactions in stars and supernova explosions Known from studying composition of meteorites composition Before and after impact differentiation begins differentiation Center heats up and gravity takes over density driven Fe migrates inward lighter material moves out Heterogeneous Earth Heterogeneous Crust Mantle Outer core (liquid Fe) Inner core (solid Fe) Lithosphere Asthenosphere Formation of the Moon A small planet collided with Earth soon after both were formed. This collision blasted debris into a ring that orbited the Earth. The Moon formed out of this ring of debris. We will discuss this hypothesis more next lecture Impact Impact Ejecta begins to aggregate into a single body Moon formation complete Nature 0658 fig2.2 Data for Earth and Moon connection 1. Studies of radiogenic elements and isotopes in lunar rocks roughly the same age, 4.5 Ga. 2. They also came from the same neighborhood: Unlike all meteorites analyzed, the nonradioactive, stable isotopes of oxygen in moon and Earth rocks match like blood types, implying the two spheres formed at the same radial distance from the sun. 3. Indeed, results from Apollo showed the pair to be more intimately connected than previously thought. Formation of the oceans and atmosphere Eventually the atmosphere developed from gases spewed out of volcanoes. When the Earth cooled enough, moisture condensed in this atmosphere to form rain that created the oceans. Relative size of planets Terrestial Planets Terrestial Planets Mercury, Venus, Earth, Mars Closest to sun - similar histories Too hot for light gases - blown away by solar winds Mercury Leaving heavy minerals Jupiter Dense rocky planets Solar wind Formed around 4.7 By Saturn Gas Giants or Jovian Planets Gas Giants or Jovian Planets • • • • Farthest from sun + similar histories Mostly volatile (gas) material Small rocky cores Mostly H and He and other light elements, commonly as ice Recent meteorite hits home in Freehold, NJ Meteorites provide the best look at the composition of the early solar system. The mass of the Earth increases every year because of 3,000 tons of meteorite debris that hits its surface from space. http://www.einsteinyear.org/facts/physicsFacts Review Solar nebula Formation of planets Condensation of sun The result! Journey to the Center of the Earth Fig. 2.05 W. W. Norton What is the Elemental composition of entire Earth? elements of earth Heavy elements left behind by solar winds In what form do we find these elements? Organic compounds Minerals Rocks Glass Metals Native Copper Melts Organic compounds Minerals Glass Rocks Metals Melts Volatiles or a gas How do we know what is down beneath the surface of the earth? How do we know what is down beneath the surface How do we know what is down beneath the surface of the earth? of the earth? The deepest research borehole ever drilled was in The deepest research borehole ever drilled was in Russia. More than a decade, a huge purpose­built rig Russia. More than a decade, a huge purpose­built rig drilled over 12 km to investigate continental crust drilled over 12 km to investigate continental crust structure. structure. It did not enter the mantle It did not enter the mantle We have only directly sampled We have only directly sampled 0.18% of the earth’s interior. 0.18% of the earth’s interior. Occasionally Occasionally deep­sourced volcanoes bring up pieces of the mantle Mantle Xenoliths “Heart of Stone”- found by a Rutgers Graduate Student Mantle Xenoliths Mantle xenolith collected in Nicaragua by Fara Mantle xenolith collected in Nicaragua by Fara Lindsay, PhD student in our department Earth’s Interior now Earth’s Crust 0­40 40 640 2891 liquid 5150 solid 6370 km So how do we know this? elements of whole earth elements Whole earth chemistry Fe 35% O 30% Si 15% Mg 10% Other 10% What is the Elemental composition of the What is the rocks at the surface of the Earth? QuickTime ™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Heavy elements left behind by solar winds Continental Crust Hawkesworth and Kemp, 2006, The differentiation and rates of generation of the continental crust, Chemical Geology Silica tetrahedron ­ SiO2 Silica tetrahedron ­ SiO Silica tetrahedra link together to make most common minerals Silicates Silicates ….most common mineral group Common minerals make up common igneous rocks Fine­grained Same rock, different grain size coarse­grained SILICIC MAFIC ULTRAMAFIC avg continental + oceanic crust Granodiorite Granodiorite Continental crust Intermediate Oceanic crust ­ mafic Basalt Gabbro Peridotite Peridotite Mantle rocks Garnet Peridotite How do we get to this?? Now the indirect methods used Now the indirect methods used to “sample “ the earth’s interior 1. Earth’s density Mass of Earth Experiment Mass Mt. Schiehallion, Scotland •Sir Isaac Newton predicted that the gravitational attraction of •Sir Isaac Newton predicted that the gravitational a nearby mountain would deflect a plumb bob from its a nearby its vertical position. In 1772 Nevil Maskelyne calculated the vertical position. In 1772 Nevil Maskelyne calculated the Earth’’s mass by measuring the deflection which provided a Earth s mass by measuring the deflection which provided a ffirst reasonable estimate of Earth's mass[by Declan DePaor] irst reasonable estimate Earth's Declan DePaor] Mass of Earth Experiment Mass Mt. Schiehallion, Scotland Density (grams/cm3) Earth’s density Earth’s density 5.5 g/cm3 = Granite Temperature oC Surface rock Density 2.5­3.0 g/cm3 Now the indirect methods used to Now the indirect methods used to “sample “ the earth’s interior 1. Earth’s density 2. Seismic waves Discovered change Discovered change in velocity with depth. Marks crust­mantle boundary, ~5­10 km beneath ocean floor ~32 km below continents. Represents change in chemical composition Mohorovicic Discontinuity (Moho) 3.5 g/cm3 seismic discontinuities Little (2%) magma bubbles Other seismic discontinuities mark density changes in the mantle 5.5 g/cm3 Dr. Inge Lehmann (1888­1993), Dr. Inge Lehmann (1888­1993), discoverer of the Earth's inner core. Danish seismologist Inge Lehmann studied the seismic waves from a 1929 earthquake near New Zealand. A few waves should have been deflected by the core, but were recorded at seismic stations. She hypothesized that the waves had bounced off some kind of boundary within the core. In 1936 she hypothesized that Earth’s center consisted of two parts: a solid inner core surrounded by a liquid outer core, separated by a discontinuity. Lehmann’s hypothesis was confirmed in 1970 with more sensitive seismographs . Now the indirect methods used to Now the indirect methods used to “sample “ the earth’s interior 1. Earth’s density 2. Seismic waves 3. Geothermal gradient Another thing about the earth Another thing about the earth ….Geothermal gradient T and P increase with depth Earth’s Interior now Crust 0­40 40 640 Crust 2891 liquid 5150 solid 6370 km Mantle Outer core (liquid Fe) Inner core (solid Fe) Earth’s Interior now Crust 0­40 40 Crust •Outer most layer. 640 •0 to 40 km deep 2891 •Continental Crust (35 to 40 km thick; Granite) liquid •Oceanic Crust (7 to 10 km thick; Basalt) solid •Lower density stiff and brittle 5150 6370 km What is the Elemental composition of the What is the rocks at the surface of the Earth? QuickTime ™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Heavy elements left behind by solar winds Lithosphere – Asthenosphere – Asthenosphere rigid, brittle, nonrigid, soft, ductile, flowable soft, flowable between 150-350 km outer 100-150 km mantle crust and top of mantle Boundary placed at 1280o C Moho Earth’s Interior now Crust 0­40 40 Mantle •2,885 km thick 640 •Largest part of the Earth by volume. 2891 liquid 5150 solid 6370 km •Peridotite dominate rock type. •Divided into upper and lower mantle. •“Soft” layer (solid but partially melted) Earth’s Interior now Crust 0­40 40 Core •Outer Core- 2,9000 to 5,155 deep. 640 2891 liquid 5150 solid 6370 km •Composed of liquid Iron (w/ small amount of other elements). •Inner Core- 5150 to 6370 km deep. •Composed of Solid Iron Crust Crust Mantle Outer core (liquid Fe) Inner core (solid Fe) Lithosphere Asthenosphere What else do we know about mother earth? magnetic dipole W. W. Norton Magnetic inclination Magnetic inclination Not measured on normal compass Modeled field lines of the electric dynamo in the liquid outer core that controls the earth’s magnetic field http://es.ucsc.edu/%7Eglatz/geodynamo.html But the earth’s magnetic field does switch 500 yrs after middle of reversal 500 yrs before 500 yrs before middle of reversal middle of reversal ...
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This note was uploaded on 04/03/2012 for the course GEOL 100 taught by Professor Neitzke during the Fall '10 term at Rutgers.

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