Chapter 28: The Planet Earth


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(Note: This reading quiz contains some material from lecture that is not found in the textbook.)

The purpose of this chapter is primarily to give an overview of the physical features of the earth and to introduce vocabulary so that we can explain (in subsequent chapters) "how the earth works."

The solar system is understood to be a remnant of the cloud of matter that condensed to form the protostar which became the sun. Thus, the planets are thought to have (about) (less than, the same?) age as the sun, which is estimated from models of the rate at which the sun produces energy from fusion and from actual measurements of ages of rock from the earth and moon to be about 4.5 (thousand, million, billion?) years. Evidence that the planets form a system with common, simultaneous origin:

  • all around the sun pretty much in the same plane;
  • all rotate (spin) in the same direction as they revolve (Uranus and Venus being exceptions).

    Unfortunately, the hydrologic system (flowing water) has eroded much of the early history of the earth. When we want evidence for the early history of the earth, we look at the .

    History of the Moon (in chronological order):

  • time of heavy bombardment (accretion) forms heavy cratering pattern to create the lunar (highlands, maria, rayed craters?) ;
  • Some very large, but relatively infrequent impact craters;
  • "Thermal event" spreads lava from the interior of the moon to form in the largest craters; and,
  • infrequent rayed craters form on top of the maria.

    When we approach the earth from space, one of the striking features is the presence of an and a hydrosphere. One of the great puzzles of Planet Earth is the presence of and oceans on its surface.

  • Continental crust (rock) is (same, different?) when compared to oceanic crust.
  • Continental crust is much (younger, older?) than oceanic crust.
  • Continental crust is much more deformed and twisted than oceanic crust.

    Additional features of continental crust:

  • On the average, continental crust is near sea level. Thus, shallow seas have often swept inland over the continents.)
  • Continental crust is typically thicker than oceanic crust. (Continental crust about 50 kilometers; oceanic crust about 8 kilometers.)
  • Continental crust is less dense than oceanic crust. (Continental crust about 2.7 grams per cubic centimeter; oceanic crust 3.0-3.2 grams per cubic centimeter.)

    The composition of continental crust is described as (granitic, basalt?) , but oceanic crust is (granitic, basalt?) . Granite and basalt are both examples of (sedimentary, igneous, metamorphic?) rock. Granite is (grainier, smoother?) than basalt. Sandstone and limestone are examples of rock. Slate and marble are examples of rock.

    Three generic (common) features of continents are:

  • shield;
  • platform; and,
  • mountains.
    The oldest and most deformed rocks are found in the (which one above?) . The mountain belts are found at the (center, edge?) of the continents and are relatively young features of the continents.

    Until after the Second World War, it is possible that we knew more about the surface of the moon than we did about the 75% of our planet under the oceans. Exploration after the War showed that there was a mountain ridge that practically girded the planet, but only occasionally protruded above the surface of the ocean. Along the top of parts of it, at least, was a crack or "rift." The generic features of the ocean basins are (moving roughly from center of the rift toward the continents):

  • oceanic ridge and rift;
  • hills on the flanks of the ridge;
  • abyssal (hills, plains?) ;
  • continental rise;
  • continental slope.

    Also found in the oceanic basins are:
  • trenches;
  • island and chains; and,
  • seamounts.





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