I thought it would be useful to have a geologic time scale on hand for reference. The Quaternary is truncated, but who cares about the Holocene? The four columns deal with different spans of time and so are not proportional to each other.
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"Ma" refers to "million years" (technically, "Ma" stands for "megaannum", "mega" for million and "annum" for years) and "Bndy Age" is just "Boundary Age" shortened. For those of you interested in such things, the colors are from the USGS, the basic design was adapted several iterations ago from a GSA timescale and has diverged in its own merry way, and dates and additional information have come from "Geologic Time Scale 2020" (Gradstein et al., editors), the International Commission on Stratigraphy, and, farther back, USGS Fact Sheet 2007-3015. (I should note that the ICS numbers are not exactly the same as the numbers in Gradstein et al. 2020.)
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