Chapter 2 presents details about the Earth’s magnetic field that build upon what you learned inChapter 1. Although the Earth’s magnetic field has only a North and South pole, the two poles (adipolar field) periodically alternate their locations while remaining near the Earth’s axis ofrotation. You also learn that when igneous rocks cool they record the direction and dip of themagnetic field in existence at that time (paleomagnetism) and that scientists can later tease thisinformation out of rocks.You learn how scientists began to couple isotopic age-dating of rocks with the rocks’paleomagnetic signatures to build detailed paleomagnetic histories. Scientists then discoveredthat each continental block had a unique paleomagnetic record, suggesting differing andconfliction locations of the Earth’s magnetic poles in rocks of the same age. Because physicistswere quite certain that the Earth’s magnetic field has always been dipolar, this led scientists topostulate that, over time, the continents might have drifted over Earth’s surface, takingindependent paths like hockey players in an ice rink.The major features of the ocean are discussed, and how patterns of earthquakes, heat flow,crustal age, paleomagnetism, and thickness of sea-floor sediment led several scientists in theearly 1960s to conclude that new crust is made at mid-ocean ridges, flows sideways away fromthe ridges, and is recycled down into the mantle at deep-sea trenches. During the 1960s, the ideaof oceanic crust being made and destroyed became accepted as a means to explain Wegener’scontinental drift and many other geologic phen=omena.You are introduced to the lithosphere and asthenosphere, the basic definition of a tectonic plate,and the three basic types of plate boundaries: divergent, convergent, and transform. You learnabout rifting of both oceanic and continental crust at divergent boundaries; why only oceaniccrust is recycled (subducted) into the mantle; and that transform boundaries generally lackvolcanism. You also learn about triple junctions and hot spots. Each of these concepts isreinforced with the study of actual boundaries and features of each type. You also learn about theforces that move plates—both ridge-push and slab-pull. The chapter concludes by showing you GPS data, which was not available to scientists until the1980s, has become proof that discrete zones of the Earth’s surface (plates) move in differentdirections and supports the theory that crust is made and destroyed at some plate boundaries.Alfred Wegner died in 1930, disgraced by most geologists for his ideas that continents haddrifted through time. Had Wegener lived another 40 years, he likely would have been thrilled bythe new data collected about the Earth and might, like the glaciologist Louis Agassiz (who westudy in chapter 18, have slowly won over the opinions of his colleagues.Chapter 2 Textbook Annotations- 2.1 Introduction o Alfred Wegener thought that continents once fit together like pieces of a giantjigsaw puzzle, to make one vast supercontinent. This is known as Pangaeao Pangaea was later fragmented into separate continents that drifted apart, movingslowly to their present positions, this is known as continental drift. o In 1960, Harry Hess and Robert Dietz, proposed that as continents drift apart, newocean floor forms between them, this is called sea floor spreading. o As the continents move toward each other when the old ocean floor between themsinks back down into the Earth’s interior, a process known as subduction. o Earths lithosphere (the outer, rigid shell) consist of about twenty distinct pieces,or plates that slowly move relative to each other. This is knowing as platetectonics. o The theory of plate tectonics: The plate movements that “build” regionalgeological features. This is how we can successfully explain many geologicalphenomena. - 2.2 Wegener’s Evidence for Continental Drift o Pangaea existed until the end of Mesozoic Era (251 – 65 million years ago). Pangaea then broke apart, and the land masses moved away from eachother, to form the continents that we see today. - The fit of the continents o All the continents could be joined, with remarkably fewoverlaps or gaps, to create Pangea. o Wegner concluded that the fit was too good to be acoincidence and thus that the continents once did fittogether.- Locations of past glaciations o Glaciers are rivers or sheets of ice that flows across theland surface. o As the glacier flows, it carries sediment grains of all sizes(clay, silt, sand, pebbles, and boulders). o Grains protruding from the base of the moving ice carvescratches, called striations, into the substrate. o When the ice melts, it leaves the sediment in a depositcalled a till, that buries striations. o Thus, the occurrence of till and striations at a location serveas evidence that the region was covered by a glacier in thepast.  By studying the age of glacial till deposits, its beendetermined that large areas of the land were oncecovered by glaciers during the time known as theice ages. - One of these ice ages occurred from 326 –267 million years ago, near the end of thePaleozoic Era. - The distribution of climatic beltso Studied sedimentary rocks that were formed at this time,for the material making up these rocks can reveal clues tothe past climate.  Equatorial: late Paleozoic sedimentary rock layersinclude abundant coal and the relicts of reefs.  Subtropical: late Paleozoic sedimentary rock layersinclude relicts of desert dunes and deposits of salt. - The distribution of fossils o Continents provide homes for different species. o Many kinds of plants grow only on one continent.  Thus, animals and plants evolved independently ondifferent continents. - When all continents were in contact, landanimals and plants could have migratedamong many continents. o The distribution of fossil speciesrequired that the continents have tohave been adjacent to one another inthe late Paleozoic and earlyMesozoic Era. - Matching Geologic Units o If the continents had been joined to create Pangaea in thepast, then these matching rock groups would have beenadjacent to each other and thus