CEE 1030 1st Edition Lecture 13 The 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 cm 3 density of granite rock CRUST 2 6 g cm 3 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 Lehrman Seismic tomography can see variations in lithosphere subducting slabs etc need high power computers to do this Earth s layered structure layers defined by 1 composition 2 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 time The 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 core