| 11. | The age of the impact event is uncertain.
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| 12. | This crater was formed following the Orientale impact event, and so is younger.
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| 13. | The Sudbury occurrence has been attributed to an impact event and associated crustal melting.
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| 14. | The meteorites cluster in families that seem to correspond to distinct impact events on Mars.
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| 15. | This became the first crater on Earth definitely proven to be from an impact event.
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| 16. | This sandstone has been fractured and brecciated by the impact event to form the rim.
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| 17. | Their presence therefore is a primary criterion for recognizing that an impact event has occurred.
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| 18. | Chapter 3 is about the process of formation of a crater during an impact event.
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| 19. | The lunar geologic timescale is based on the most prominent impact events, including stratigraphic horizon.
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| 20. | Current archaeological thought dates souterrains as late Iron Age, thousands after the supposed impact event.
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