Why is time important for science? 4.6 Billion years The Geologic Time Scale is a broad division of time that chunks the Earths history five ways, based upon specific characteristics in the geologic record. It utilizes geologic and biologic events. It was first proposed in 1913 by British geologist Arthur Holmes. Two or more geological eras form an Eon, which is the largest division of geologic time, lasting many hundreds of millions of years. Broad time spans based upon the characteristics of life (Biologic Events) Two or more geological periods comprise an era, which is hundreds of millions of years in duration. Shorter time spans based upon major disturbances of the Earths crust (Geologic Events) The period is the basic unit of geological time in which a single type of rock system is formed, lasting tens of millions of years. Short time spans which are subdivisions of the periods An epoch is a division of a geologic period; it is a small division of geologic time, lasting several million years An age is a unit of geological time which is distinguished by some feature (like an Ice Age). An age is shorter than epoch, usually lasting from a few million years to about a hundred million years. The Geologic Time Scale is arranged chronologically, with the oldest events at the bottom and the most recent events at the top. The Geologic Time Scale combines two types of time: Relative Time Time based upon the relationships of (igneous) rocks or approximate orders of events Absolute Time Time based upon units stated with numbers Geologic Time Line The age of the earth is estimated at 4.6 billion years. That span of time is difficult to imagine. The following examples may help: How Big is a Billion? One sheet has 4000 asterisks. 500 sheets would have 2 million asterisks How many sheets for a billion asterisks? It would take 250,000 pages or 500 bundles to show one billion asterisks! You would need a stack of paper over 83 feet tall!!! Other Billion examples: Save a billion $- you save $100 a day for 27, years Count to a billion- 3 seconds per number would take you 95.1 years Walk a billion steps- each step at 2 feet per step will take you times around the equator.