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Chapter 8 Geology

• "... Earth is a giant heat engine, and hot things are forever struggling to cool themselves down. This is the most telling way to think about our planet ... as a great hot ball trying to shed thermal energy into space." [p. 217]
  
  
• "The core of Earth is almost 6000 degrees Celsius. The space through which Earth is hurtling is about -270 Celsius." [p. 217]
  
  
• "Earth condensed about 4.5 billion years ago from the ring of rock and dirt that remained after the formation of the sun ... Denser materials like iron and nickel were tugged most strongly by the planet's gravitational field and gradually migrated toward the center. Lighter elements, inlcuding oxygen and silicon, felt less of a pull and formed intermediate and outer layers." [p. 218]
  
  
• "Earth's core, its compacted ball of iron, nickel ... is really a ball within a ball, an inner zone about the size of the moon ... surrounded by an outer core about the size of Mars." [p. 219]
  
  
• "The inner core is ... hot enough to melt iron ... but the pressure is so great that the atoms cannot flow and so the inner core is a solid." [p 219]
  
• "In the outer core, pressures are a bit more relaxed, ... and the iron slips around like a liquid. As the molten metal of the outer core glides around the solid iron of the inner, the motions generate Earth's magnetic fields. ... These magnetic fields help to deflect much of the solar wind, the high-energy particles that stream from the surface of the sun. ... Together air and magnetic fields scatter most solar X-rays, cosmic rays and gamma rays." [p. 219]
  

• "The concentration of iron, nickel, and their atomic ilk in the core, to the near exclusion of the lighter elements, makes for an unmistakable boundary between core and noncore. This adjacent layer is called the mantle. ... The difference in density between core and mantle is as extreme as the difference between the surface and the air above it." [p. 220]
  
  
• "Most of the Earth's girth is taken up by the mantle. The mantle is more like Silly Putty. It is solid, but it can move, and it does all the time." [p. 220]
  
  
• "Above the mantle is the ... crust." [p. 220]
  
  
• "The crust is composed of relatively light rocks buoyed atop the conensed superputty of the mantle. The crust is also the coolest part of the Earth, and thus is brittle and prone to fracturing." [p. 221]
  
  
• "In general, continental crust is about six or seven times thicker than oceanic crust." [p. 221]
  
  
• "... in fact much of the seabed is quite young, hundreds of millions of to billions of years younger than the dry land." [p. 221]
  
  
• "... theory of plate tectonics, a fundamental organizing principle of geology and one of the grand discoveries of the twentieth century." [p. 221]
  
  
• "By general consensus, there are seven to ten large, or major plates, and twenty-five to thirty minor ones." [p. 223]
  
  
• "The plates are about fifty miles thick, although they vary in density. ... The plates bearing the continents are relatively thick and light, while those scalloped with ocean basins are thin and dense. ... The upper part of each mobile plate, the crusty part, is brittle and prone to cracking and crumbling. The nether portion, in the mantle, is hotter and more plastic, more likely to yield when pressed. ... All the plates are sliding over, or in some cases with, the more viscous lower mantle beneath." [p. 223]
  
  
• "In a million years, a plate migrates some 30 miles. Give a plate 100 million years, and it will have globetrotted 3,000 miles." [p 223]
  
  
• "Early in the evolution of the solar system wild swarms of comets (chunks of ice and dirt) were attracted by Jupiter but missed it and ended up hitting Earth. Some of this ice vaporized back into space but some of it seeped into the rock. ... About 4 billion years ago volcanic activity helped free this water from the rock and it began to form huge clouds which eventually supersaturated the atmosphere and it then rained for hundreds of thousands of years, filling up the ocean basins." [p. 228]

Chapter 9 Astronomy

• "Of the many extraordinary findings in astronomy over the past half cntury or so, space scientists cite two as cosmic standouts: the discovery and elucidation of the Big bang that rang in our universe and the surprising centrality of ancient stars to the rise of life on earth." [p. 239]
  
  
• "Using mathemtical models, scientists have chased the universe back to point close to the Big Bang ... to 10*-35 seconds after time zero." [p. 243]
  
  
• It was early stars that formed most of the elements which eventually permitted the possibility of organic compounds forming.