| 31. | North America is the source of much of what humanity knows about geologic time periods.
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| 32. | Over geologic time crustal movement brought these injected igneous rocks to the surface of the earth.
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| 33. | That's sudden on the scale of geologic time.
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| 34. | Like Mercury; this is probably due to slumping of the weak icy crust over geologic time.
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| 35. | Limestones have accumulated over billions of years of geologic time and contain much of Earth's carbon.
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| 36. | Since 1977, stages on the geologic time scale.
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| 37. | Additionally, in geologic time scales, the ice caps may grow or shrink due to climate variation.
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| 38. | In geologic time, that's not even an eyeblink.
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| 39. | Developing a sense of geologic time is frightening.
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| 40. | Since its primordial beginnings, life on Earth has changed its environment on a geologic time scale.
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