It's pretty cool. The farther back we go, the fewer divisions (supereon, eon, era, period, epoch). The more recent, the more divisions. For example, the mesozoic era is further divided into three periods, but the periods are not further divided into epochs.
However, the current era, the Cenozoic Era is divided into periods also, the paleogene, the neogene, and the quaternary. With these periods, for the first time, we have epochs.
The paleocene has three epochs, the neogene has two epochs, and the quaternary has two epochs, the Pleistocene and the Holocene.
And with the epochs we have "ages" which I think may or may not be the best choice of words.
Whatever.
The four ages of the Pleistocene epoch: Gelasian; Calabrian; Middle; and, Late.
The current epoch, the Holocene epoch does not yet have "ages"?
Of course that's one of the problems for newbies: when scientists talk of the various "ages," they do not specify eon, or era, or period, or epoch. They will toss around "Devonian" and "Cambrian" in same sentence, for example. One if the fourth period of an era, whereas the other is the first period of the same era, but confusingly, the Precambrian is a supereon. There apparently is no name for a supereon that follows the Precambrian. By default, it would have to be the Postcambrian (which is not quite correct, because the Postcambrian would also include the Cambrian period).
It appears there was only one supereon.
The Precambrian supereon was made up of three eons. After the supereon Precambrian, and after the three eons of the supereon Precambrian, there has been only one additional eon, the Phanerzoic eon. The Phanerzoic life, from the Greek visible life, is the eon of abundant life. Prior to the Phanerzoic there was life, but not well understood.
The eon of visible life, the Phanerzoic Era has three era: the paleozoic (fish); mesozoic (reptiles/dinosaurs); and, cenozoic (mammals).
From wiki:
No comments:
Post a Comment