Earths` geological History is divided into different categories, going Eon > Era > Period > etc etc
Further info (Wikipedia)The Paleozoic Era, spanning 538.8–251.902 mya(million yrs ago), marks the development of our current animal phylums, such as chordata and arthropoda(my personal fav). Periods(sub categories) of the Paleozoic Era include(these are just the ones ive focused on most, feel free to make your own research and contact me if you want to yap about it):
Paleozoic, esp Cambrian, Animals have a reputation for looking as if mother nature was on an acid trip. If life on earth can be this sillygoofy, just imagine what alien life could be like :o I would like to learn much more about botany but as of now, im more of a microbe and animal type gal, meaning this list will focus most on animals