Outline of the Timeline

The Archean Eon and the Proterozoic Eon make up the Precambrian, starting with Earth's beginning at 4,500 million years ago (Ma) and going to about 542 Ma. Life first appeared during the Archean, perhaps as early as 3,800 to 3,500 Ma, as single-celled organisms. Such simple life-forms dominated the Precambrian, leaving little fossil evidence. Finally, just before the end of the Proterozoic Eon, larger organisms appear, but their soft bodies only form fossils under special conditions. Until recently in fact, they were not even known to exist. The first case in the Life Through Time exhibit explores the Precambrian, including fossil organisms and the effects of life on Earth's geology.

The third, Phanerozoic Eon, begins about 542 mya with the appearance of hard-bodied or shelled organisms. The occurence of hard body parts also signals the beginning of the main fossil record at the beginning of the Cambrian Period.

The Phanerozoic Eon is divided into three Eras: the Paleozoic Era (542-251 Ma), the Mesozoic Era (251-65.5 Ma), and the Cenozoic Era (65.5 Ma-present).

twelve cases in the Natural History Museum correspond to the twelve periods of the Phanerozoic. Thus we see cases for the six periods and subperiods of the Paleozoic Era: the Cambrian, the Ordovician, the Silurian, the Devonian, the Carboniferous (two cases for Mississippian and Pennsylvanian subperiods), and Permian.

Three cases comprize the Mesozoic Era, "the Age of Reptiles", one each for the Triassic, the Jurassic and the Cretaceous Periods.

Finally two cases, one for the Paleogene, and one for the Neogene comprise the Cenozoic, "the Age of Mammals", or Recent Era.

Additional cases address specific aspects of the fossil record. You will find links to some of these displays as you explore the Life Through Time Timeline. Others may be accessed through the main Exhibit page.