Introduction to Life Through Time Exhibit

Richard A. Paselk, Associate Curator

Thirteen display cases at the HSU Natural History Museum address the theme of changes of Earth and its inhabitants over time. The history of Earth is divided into three major time periods, or eons.

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).

Eleven cases in the Natural History Museum correspond to the twelve periods of the Phanerozoic. Thus we see cases for the first five periods and subperiods of the Paleozoic Era: the Cambrian, the Ordovician, the Silurian, the Devonian, the Mississippian, and the Pennsylvanian.

The last period of the Phanerozoic, the Permian, is combined with the first period of the Mesozoic, the Triassic, in a single case.

Two more cases finish the Mesozoic Era, one for the Jurassic Period and one for the Cretaceous Period.

Finally two cases, one for the Paleogene, and one for the Neogene comprise the Cenozoic 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 Exhibit. Others may be accessed through the main Exhibit page. You may also access the life through time cases via links on the Life Through Time Mural or the Geological Timeline:

Life Through Time Mural

Geological Timeline