CEE 1030 1st Edition Lecture 13The Earth’s interior -Distance from center of earth to surface: 6371 km (factor of 500x deeper) -samples of deep crust and upper mantle: ex. xenoliths in some lavas baseball analogy can we figure out what is inside a baseball without cutting it in half?can measure:- mass of baseball (g)- volume of baseball (cm3)- calculate density= mass/volume Can calculate the average density of planet earth -average density of planet earth- 5.5 g/cm3- density of granite rock= CRUST- 2.6 g/cm3- Iron (+5-10% Nickel)- the only common elements in the solar system with right density (10-12 g/cm3) seismology- the study of seismic waves generated by earthquakes and large explosions - much of our knowledge about earth’s interior comes from seismology - behavior of seismic waves provide critical information about the interior of the earth seismic waves move at different velocities through rocks with different properties: density, elasticity, composition pressure, and temperature - at boundaries between materials with different properties, seismic waves change speed and direction: reflection and refraction These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Body Waves - P waves: primary, ‘push-pull’, compressional - P waves always travel faster than S waves- P waves can be transmitted through liquid - S waves: secondary, ‘shaking’, shear- S waves can not be transmitted through liquid Global network of seismic stations- established to monitor international nuclear bomb test ban treaties The crust- mantle boundary The Moho (Mohorovicic discontinuity) discovered in 1909 by Andriaja Mohorovicic seperates crustal rocks from underlying mantle The core- mantle boundary - discovered in 1914 by Beno Gutenberg- boundary between Inner core and Outer core discovered in 1936 by Inge LehrmanSeismic tomography - can see variations in lithosphere, subducting slabs etc. - need high- power computers to do this Earth’s layered structure- layers defined by:1. composition2. physical properties such as mechanical strength The Core The core- an iorn- rich sphere with a radius of 3486 km – larger than the planet mars Inner core- solid inner sphere 1216 km radius Outer core- liquid outer layer ~ 2270 km thick -average density is ~11 g/cm3- mostly iron, with 5% to 10% nickel + lesser amounts of lighter elements -repsonisible for earth’s …..-Evidence for core composition?- iron is the only common element in the solar system that has the right density to form core.- iron meteorites also contain 5-10% nickel Early differentiation- dense iron sank to form core, light silicate minerals formed mantle Earth’s magnetic field -large permanent bar magnet deep in earth? Unlikely. Temperatures too hot for any material to retain its magnetism - movement of electrically- conducting liquid iron in outer core geodynamo- earth’s inner core is getting bigger over timeThe mantle - solid rocky (silica- rich) shell that extends to a depth of ~2900 km (1800 miles) - makes up 82% of earth’s volume - composition= ultramafic rock, peridotite - upper mantle= olivine + pyroxene minerals - lower mantle= denser more tightly- packed versions of these minerals - upper/ lower mantle boundary at 670 km The crust - earth’s thin outer skin: range in thickness from ~ 3 km (2 miles) at some oceanic ridges to ~80 km(50 miles in some mountain belts) - comprises 0.6% of earth’s volume - two distinct types: 1. oceanic 2. continental different ages and compositions The oceanic crust oceanic crust- density ~3.0 g/cm3-composition= mafic igneous rock basalt -oceanic crust is young (< 200 Ma and then)The continental crust continental crust: density ~2.7 g/cm3- composition= felsic igneous rock andesite - some parts of continents are ancient (2-4 Ga)Layers defined by physical properties- with increasing depth, earth’s interior is characterized by gradual increases in temperature, pressure and density - depending on temperature and depth, earth materials may behave like: 1. a brittle solid 2. deform in a plastic- like manner and flow 3. melt and become liquid lithosphere (“rock” sphere)- relatively cool, outer rigid shell of earth. - forms the earths tectonic plates that move - comprises crust + uppermost mantle - varies in thickness from 70 km to 250 km asthenosphere- (“weak” sphere)- soft, comparatively weak layer of upper mantle beneath the lithosphere. Close to our at melting point- small % of melt present Earth’s internal heat engine - earth’s temperature gradually increases with depth at a rate known as the geothermal gradient - heat transferred through lithosphere by conduction Plate tectonics and internal heat- major sources of earth’s internal heat heat from radioactive decay of isoptopes of uranium, thorium, and potassium heat releases as iron crystallized to from the solid inner
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