Geologic Time Scale

How Old is Earth? There are 2 main opinions:
- Geologists belive it is about 4.5 billion years old
- Creationism says that it is about 6000 years old
History of The Scientific Geologic Time Scale

    The Geologic Time Scale is an idealized model used by earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth.  The scale has been organized into various units according to events which took place in each period. Different spans of time on the time scale are usually separated by major geological or paleontological events, such as mass extinctions. For example, the extinction of dinosaurs marked the end of the Cretaceous and the beginning of the Paleogene periods.The table is split up into 3 categories called Eras, Periods, and Epochs. According to the Geologic Time Scale the Earth is approximately 4.570 billion years old.

Important Definitions
The longest division of geologic time made up of one or more periods.

A unit of time, longer than an Eoch and shorter than an Era.

A unit of time that is a division of a period.

Extinction Event-
A sharp decrease in the number of global species in a relatively short period of time. (mass extinction)

Index Species-
Species that are found only in a certain period of time (if found scientists can date the fossil and rock around it).

A remnant or trace of an organism of a past geologic age, such as a skeleton or leaf imprint, embedded and preserved in the earth's crust.

Analogies for Human"s Time on Earth

If the 12 hours showing on the dial are equal to earth's history of 4.5 billion years, humans arrived only half a minute before 12. This means that the entire human history is just 10 seconds old - because the chain of evolution from the great apes to humans actually took up 20 seconds.