The Geologic Time Scale

Part 1

The Geologic Time Scale

The Geologic Time Scale The Geologic Time Scale is a system of chronological measurement that relates stratigraphy to time. Stratigraphy is a branch of geology which studies rock layers and layering (stratification.) It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy includes two related subfields: lithologic stratigraphy or lithostratigraphy, and biologic stratigraphy or biostratigraphy, and is used by geologists, paleontologists, and other earth scientists to describe the timing and relationships between events that have occurred throughout Earth's history.

The Geologic Time Scale This scale divides geologic history into units, with the following subdivisions: Eons are the greatest expanse of time. There are three (or four) eons: Hadean - the first eon Precambrian - further subdivided into the Achaean and Proterozoic eons Phanerozoic - the most recent and current eon Eras are subdivisions of an eon. For example, the eras of the Phanerozoic eon are: the Cenozoic (“recent life”) the Mesozoic (“middle life”) the Paleozoic (“ancient life”) Eras are further subdivided into periods. Periods are further subdivided into epochs.

The Geologic Time Scale Eon Eras Periods Epochs

The Geologic Time Scale

The Geologic Time Scale Geologic time is divided into two eons, but one of these is divided into sub-eons. the Precambrian (ancient) Eon the Achaean Sub-Eon the Proterozoic Sub-Eon the Phanerozoic (current) Eon

The Geologic Time Scale In this two eon-system, the Precambrian Eon can be said to have began with the creation of the Earth about 4.5 billion years ago and ended about 542 million years ago. The Achaean Sub-Eon began with the creation of the Earth and ended about 2.5 billion years ago. The Proterozoic Sub-Eon began about 2.5 billion years ago and ended about 542 million years ago. The Phanerozoic Eon began about 542 million years ago and continues to the present day.

The Geologic Time Scale Eons are further divided into Eras. Archean Eon Eoarchean Era Paleoarchean Era Mesoarchean Era Neoarchean Era Proterozoic Eon Paleoproterozoic Era Mesoproterozoic Era Neoproterozoic Era Phanerozoic Eon Paleozoic Era Mesozoic Era Cenozoic Era

The Geologic Time Scale The Phanerozoic Eon is further divided into Periods. Phanerozoic Eon Paleozoic Era Cambrian Period Ordovician Period Silurian Period Devonian Period Carboniferous Mississippian Period Carboniferous Pennsylvanian Period Permian Period Mesozoic Era Triassic Period Jurassic Period Cretaceous Period Cenozoic Era Tertiary Period Quaternary Period

The Geologic Time Scale The Cenozoic Era is further divided into Epochs. Cenozoic Era Tertiary Period Paleocene Epoch Eocene Epoch Oligocene Epoch Miocene Epoch Pliocene Epoch Quaternary Period Pleistocene Epoch Holocene Epoch

LAB

Lab- The Geologic Time Scale

The Geologic Time Scale Figure 11.19 The Geologic Time Scale