This illustration shows a rock column. Using potassium-argon dating, geologists have calculated an age of 200 million years for rock A, a granite. Rock F, the volcano, has been given an age of 225,000 years. Use the ages and illustration to answer the questions.
1. Did the canyon form before or after layers B, C, D, and E?
How do you know?
2. Did rock B form before or after rock C?
How do you know?
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