The Following Questions Refer to the Description and Figure Below

question 66

Multiple Choice

The following questions refer to the description and figure below.
The figure represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley) , the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about 1 million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley.

Figure 25.1
-Assuming that the rate of sea-floor spreading was constant during the 1-million-year period depicted above, Earth's magnetic field has undergone reversal at an average rate of once every

• A) 10,000 years.
• B) 25,000 years.
• C) 100,000 years.
• D) 250,000 years.
• E) 1,000,000 years.

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Mars

Fourth planet out from the Sun.

Creative Leap Approach

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