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Crystal Structures of Metals

Pure metals adopt one of three packing arrangements

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To the Center of the Earth

To the Center of the Earth

Credit: NASA/Goddard
Source: http://www.flickr.com/photos/24662369@N07/5710028991
License: CC BY-NC 3.0

We can go to the Moon and explore its make-up. We can study the planets and the Sun to get an idea of their compositions. We can study our own planet, but only on or near the surface. Under the Earth we can only travel 2.4 miles before stopping. Beyond that, we have very little solid data as to what the interior of the Earth is like.

Amazing But True

  • What’s at the center of the Earth? Many civilizations have speculated about this question, but obviously nobody has been there to see. Most of the myths revolve around some deity or another who dwell at the Earth’s core. Many legends involve a hollow Earth of some sort, often with palaces and cities. Modern science fiction has also played a role in these speculations, from Jules Verne’s A Journey to the Centre of the Earth to more contemporary versions.
  • Scientific data about the core of the Earth strongly suggests that it is primarily iron. This theory is supported by studies of the composition of the Sun and of meteorites, as well as studies to see how the core responds to seismic waves passing through the core. The presence of iron in the core is believed to be the explanation for the magnetic fields of the Earth.
  • Credit: Hendrik Kueck
    Source: http://www.flickr.com/photos/hendrik/5103219/
    License: CC BY-NC 3.0

    The relative size of the Earth's core to the rest of our planet [Figure2]

  • At the very center of the core, the iron is thought to be solid. Even though very high temperatures exist at the center of the Earth (estimated to be somewhat greater than 5400°C), there are also high pressures. On the surface of the Earth, iron exists in three different crystalline forms. However, recent studies indicate that one of those forms cannot exist at high pressures. Seismic studies narrowed the crystal structure down to the hexagonal close-packed form. This finding also explains whys seismic waves travelling North-South have a slightly higher speed that those travelling East-West. It is theorized that the crystals achieve a specific alignment as they form which affects the rate of passage of energy.
  • Watch a video about the interior of the earth at the link below:


Show What You Know

Use the links below to learn more about the core of the earth. Then answer the following questions.

  1. What is thought to produce the hexagonal crystal structure of iron at the core of the earth?
  2. Is iron always magnetic?
  3. What is one theory of how iron got to the earth’s core?
  4. What have scientists discovered about rotation of the core?

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    Image Attributions

    1. [1]^ Credit: NASA/Goddard; Source: http://www.flickr.com/photos/24662369@N07/5710028991; License: CC BY-NC 3.0
    2. [2]^ Credit: Hendrik Kueck; Source: http://www.flickr.com/photos/hendrik/5103219/; License: CC BY-NC 3.0

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