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| Rocks are often the only witnesses to a planet's distant past. Their color, shape, and scars tell a story about what happened to the planet long ago. Rocks are usually found in layers with the oldest at the bottom and the youngest at the top. But a major event, such as an earthquake or an asteroid impact, disrupts these layers, leaving behind a record of when and where catastrophic events occurred. |
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Examines rocks to learn about a planet's history |
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"It's the dream of every child to get to play in the dirt. We geologists get to do it for real." 
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