The Geologic Timeline

Geologic Time Scale ► The division of Earth’s history is divided into units of time, based on the fossil records contained in the rocks. ► The Geologic Time Scale is broken-up into four major divisions… ► Eons, Eras, Periods, Epochs

Eons of Geologic Time ► These are the largest division ► They are measured in hundreds of millions to billions of years ► There are four of them  Hadean  Archaean  Protoerozoic  Phanerozoic ► Hadean, Archaen and Proterozoic are often classified as “Precambrian Time”

Precambrian Time ► The Hadean Eon (4.6 – 3.8 Billion Years Ago)  Earth cooled and formed from a cloud of gas, and from asteroid collision.  Iron and Nickel sank to the core.  Oxygen and Silicon rose to the surface.  Earth’s solid surface is created  (Hadean is sometime not recognized) ► The Archaean Eon (3.8 – 2.5 Billion Years Ago)  An early atmosphere develops  Ancient oceans develop  Continent-building occurs  The first forms of life (bacteria) arrive ► The Proterozoic Eon (2.5 Billion – 543 Million Years Ago)  Single, super continent of Rodinia forms  Atmosphere becomes oxygen-rich  Multi-cellular plant and animal life develops

Eras of Geologic Time ► The Eras are the second longest division of the geologic time scale ► They are measured in hundreds of millions of years ► They are defined by the life forms found in the rocks as fossils

The Phanerozoic Eon, and the “Big Three” Eras ► The fourth Eon (Phanerozoic) contains the only real Eras...  The Paleozoic Era ► An explosion of life forms ► Fish develop ► Life comes on land ► Giant insects  The Mesozoic Era ► Pangaea is formed ► Reptiles and Dinosaurs thrive  The Cenozoic Era ► Flowers, Birds and Mammals thrive ► Pangaea breaks up ► Volcanoes and Mt. Building occur ► Remember that an Era is defined by the different life forms found as fossils in the rocks.

Periods of Geologic Time ► Geologic Periods are defined by the life forms that were abundant, or became extinct. ► Each Era is broken-down into multiple Geologic Periods, based on the life forms that thrived or died ► They are measured in millions to tens of millions of years

Epochs of Geologic Time ► These are the smallest of the major divisions ► They are measured in millions of years to tens of millions of years ► They are distinguished by different groups of organisms

So where are we… ► We are in the…  Phanerozoic Eon…  The Cenozoic Era…  The Quaternary Period…  The Holocene Epoch.

A “graph” representing Geologic Time ► Label the…  The Hadean Eon,  Archaean Eon,  Proterozoic Eon ► Label all three of the early Eons as “Pre-Cambrian” Time. ► Label the…  Paleozoc Era  Mesozoic Era  Cenozoic Era ► Label all three of these Eras as the Phanerozoic Eon.

A “football field” representing Geologic Time