Geo 101N 1st Edition Lecture 4Outline of Last Lecture I. Earth Compositiona. Planetsb. DifferentiationII. Moon III. Earths compositionIV. Formation of the Oceans and AtmosphereOutline of Current Lecture V.Magnetic Field continuedVI. Plate TectonicsVII. Alfred WegnerCurrent LectureI. Magnetic Fielda. Movement of electrically chargedparticles creates the magnetic fieldb. The field around a bar magnet canbe revealed using iron filings c. Earths magnetic field protectsthe earth from solar windsd. The field is weakest at the poles, which iswhy we see the aurora’s theree. Iron-bearing materials record thedirectionality of the magnetic field whenthey coolII. Auroraea. Some ions from the solar winds travelcloser to earth following field linesb. Spectacular following a solar storm/flaresc. Aurora borealis = north; Aurora australias= southIII. Rock Magnetisma. Reveals that the magnetic field has reversed in the pastb. Stacked lava flows that have reversed N/S magnetic polesIV. Magnetic Field Reversalsa. Happen ~250,000 mya the polarity reversesThese 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.b. Strength of the field has dropped ~10% in the last 150 yearsc. Perhaps we are approaching a reversal againd. Reversals have been modeled using supercomputers; shows that the last reversaltook ~100 years and happened ~780,000 years agoV. Plate Tectonicsa. Development of the theory of plate tectonics revolutionized the way people think about the earthb. Hundreds of geologists working with different types of data contributed to the eventual acceptance of the theoryc. = paradigm shifVI. What came before the plate tectonics field?a. The contracting earth model: the earth was/is slowly cooling and contracting as heat from the formation is losti. Mountains are just “wrinkles” formed due to the contraction of the earthii. Ocean basins are caused by surface collapsesiii. The continents were static (not moving)iv. Vertical motion is the only real movement of the earths surfaceVII. Alfred Wegnera. The coasts of Africa and South America are eerily similar = observational b. In the early 1900’s several scientists, including Wegner, proposed versions of continental movement theoriesc. Called “mobilists” to belittle their ideasd. Wegner published in 1912; based his model on observational evidencee. Mobilists, and Wegner, were doubted because he had no mechanism to explain “continental drif”VIII. Continental Drifa. Continents have occupied different locations in the pasti. ~250mya all continents were stuck together = Pangeaii. Continents “drifed” across the earths surfaceb. Evidence:i. Fossils-plants and animals that don’t travel easily; iemesosaurs, a freshwater reptileii. Shapes of modern continentsiii. Glacier locations/evidence of their flowiv. Matching features such as Africa and the Appalachian Mountains in NorthAmerica and the South American continentIX. Wegner’s Hypothesisa. Consistent with evidenceb. Ignored by other geologists-no mechanismc. Opposition came up with alternative hypothesisX. Wegnera. Died in 1930 @ the age of 50 doing field research in Greenlandb. His science was lost w/o an advocate then WWII happened; it wasn’t until the 1950’s when his idea was revived c. The development of new science (radar) and the discovery of new observational