Chicxulub Impact Crater

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Chicxulub Impact Crater
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Learning Experience 1 Using gravity anomalies
to locate the Chicxulub impact crater

• In part 1, learners to create a contour map
  where local measurements of the Earths gravity
  have been recorded over Mexicos Yucatan
  peninsula.
• Learners examine the contour map that they have
  drawn to see if they can discern a pattern in the
  data that suggests the existence of a feature
  that could be an impact crater. To expedite the
  lesson, the data points have already been
  correctly positioned on the worksheet, which is
  located in the student handout.
• The second part repeats the process with the aid
  of a computer. A software program called
  Surfer can produce sophisticated results in a
  matter of minutes. The input gravity data file
  has been prepared in advance. With Surfer the
  computer is doing the same thing that learners do
  by hand.

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Background

• Geophysicists use gravity surveying to
  investigate subsurface geology on the basis of
  variations in the Earths gravitational field
  that result from the differences of density
  between subsurface rocks.
• At the Earths surface, the mean value of
  gravity is 9.8 m s-2 (meter per second per
  second).
• Variations in gravity caused by density
  variations between rocks are much smallerabout
  100 mm s-2 (micro meter per second per second).
  In geophysics, the unit of 10-3 cm s-2 is the
  milligal (mGal). Deviations of the local or
  regional gravity from some reference state are
  gravity anomalies.
• Gravity anomalies are associated with large
  meteor impacts because the resulting crater is
  often filled by melted sheets of rock and
  sedimentary rocks called breccias. These have a
  relatively low density. Since the rocks that
  fill the crater are less dense than the
  surrounding strata, the gravitational field near
  the crater is weaker than the background
  measurements.

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Critical Thinking Questions

• Whats the difference between a comet, an
  asteroid, a meteor, and a meteorite?
• How can measurements of the Earths gravity
  fields help us to locate impact craters that have
  been buried by sediments?
• Did our interpretation of the gravity data prove
  the existence of an impact crater at Chicxulub?
  Why or Why not?
• If a scientist finds an anomalous ring in his/her
  gravity data and suspects that it is the result
  of an meteor impact, what other forms of evidence
  would support his/her theory?
• Describe the effects on a large meteor impact on
  Earth processes. In particular, focus on
• A) the atmosphere
• B) the oceans and the land
• B) climate and
• C) plants and animals.

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Learners appreciate of the importance of
multiple lines of evidence in supporting a
hypothesis
seismic
lithology/mineralogy
gravity
cenotes