This longest division of geologic time doesn't have a fixed period; in astronomy, it's one billion years
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Craters Dantu and Haulani both formed recently in geologic time, but also ... Now 
in its extended mission, the Dawn spacecraft has delivered a wealth... [DOC] [TLE] The Emerging 'Sunspot Cycle 24' and A Weakening Magnetic Field ... [PAR] Feb 25, 2009 ...