Universe Cycle - Solar System (5)
 Lab 

   
OBJECTIVES:
  • Comparing meteorites to Earth rocks.
  • Learning names for meteorites.
VOCABULARY:
  • meteor
  • meteorite
  • meteoroid
  • asteroid
  • tektite
  • rock
MATERIALS:

Students examine a tektite and compare it to Earth rocks


Meteorites

BACKGROUND:



Meteorite impact crater in the 
Australian outback

A meteoroid is a naturally occurring, relatively small, solid body. Bodies larger than 1 kilometer in diameter are usually called asteroids. Meteoroids and asteroids move quickly, at speeds of greater than 10 km/second, about 58,000 miles per hour!

When a meteoroid enters through the Earth's atmosphere, it is slowed by friction with atmospheric molecules. This causes the meteor to heat up. It often glows, and leaves a trail of vaporized material and ionized air behind it. A glowing meteoroid moving through the atmosphere is called a meteor. Meteoroids enter the Earth’s atmosphere continuously. Most of these objects, however, are dust to sand sized particles, which burn up, or vaporize, high in the atmosphere.


Regmaglygt texture of meteorite 
from Sikhote Alin, Russia

If a meteor survives its passage through the atmosphere and strikes the Earth’s surface, it is called a meteorite. This can happen in two ways. Some meteors disaggregate or explode in the atmosphere, and their remnants fall to the surface. If a meteor travels all the way to the surface, it usually creates a crater. The energy of the meteor compresses the ground where it strikes, forming a hemispherical cavity. In addition, much of the meteor, and some of ground is vaporized.

Material is also ejected from the crater, landing in piles all around it. This material may include bits of the meteor and surface rocks, as well as molten rock formed by the energy of the impact. This molten rock is similar in appearance to terrestrial magma. In some impacts, large blobs of molten rock are flung outward. These strike the surface and quickly cool, forming glassy objects called tektites. Tektites in this scenario are considered primarily melted Earth materials that sprayed upward and outward during an exceptional meteorite impact.


Camel Donga meteorite from Australia

Meteorites and tektites are rare for three reasons. First, much of a meteorite is vaporized during its impact with the surface. Second, after they reach the Earth’s surface, meteorites and tektites are subjected to weathering and breakdown. Third, these objects may be buried by the deposition of sand, mud, or other sediment.

Meteorites have three general compositions:

  1. Iron meteorites are composed mainly of metallic iron and nickel, often mixed together as an alloy. 
  2. Stony meteorites contain mainly silicate minerals, such as pyroxene, plagioclase feldspar, and olivine. They also contain minor amounts of metals, particularly nickel and iron alloys. Stony meteorites account for 95% of all meteoritic material. 
  3. Stony-iron meteorites contain a mixture of silicate minerals and nickel-iron alloy. Stony meteorites are similar to igneous Earth rocks like basalt. Iron meteorites probably resemble the material in the Earth’s core.

You may wish to tell the students that their tektite samples are from Thailand, and are about 1.2 million years in age. They came from a crater that has not been found, but was probably someplace in Cambodia. Tektites from this impact have been found as far away as central Australia.

PROCEDURE:

In this lab the students will compare meteorites with Earth rocks and then see what happens to a meteorite when it hits the Earth's surface.

  1. The students have samples of granite, basalt, obsidian, sandstone, and schist from Earth. They also have a small meteorite to use for comparison. This sample is a tektite from Indonesia. Tell students to compare and contrast the samples.
     
  2. In this lab the students will compare samples of tektites with five Earth rocks: granite, basalt, obsidian, sandstone, and schist. They will probably conclude that the tektite is most similar to basalt or obsidian because both samples will be black in color and contain visible minerals. However the composition of tektites is more similar to obsidian. Basalt is actually quite different; the tektites contain much more silica. The granite, sandstone, and schist do not resemble the meteorite at all.


Tektite collection

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