Just as a lark and as a little exercise in making HTML tables (and to make clear what one error was in that last post), I threw together this table of the geological time scale, taken from Mayr’s What Evolution Is. I come from that generation of biologists where we were required to memorize the timescale to this level of detail; I’m a bit rusty on the dates now (but these are pretty much the same as what I had to learn in the late 1970s), and I was just realizing that we don’t even mention this stuff in introductory biology anymore.