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Esimerkit

• 1967, Rankama, Kalervo, Institute of Geology and Mineralogy, University of Helsinki, Helsinki, Finland, Megayear and Gigayear: Two Units of Geological Time
• These syntheses gave a fresh geological, as opposed to solely geophysical, view of the up to multi-megayear and near gigayear mechanism responsble for the palimpsests of a general process of change in the upper crust: a process that we may observe, often apparently 'frozen' -- because it is so slow, at different steps in the process, in different places within the upper crust.
• The illustrative example here provides for a few gigayear spread in ages of tracers of the stellar halo in a spiral (this is obviously sensitive to the chosen turnaround redshift) as found for the Milky Way field stars (Schuster & Nissen 1989) and globular clusters (reviewed by Bolte 1993).
• It's hard to tell the difference between a 5-gigayear, 8-gigayear, and 10-gigayear cluster for such a sparse object as this unless you've got very high-quality photometry.
• The fraction could be as high as 100% if the nuclear activity lasts much less than a gigayear.