Earth's History/Geologic Time Reduced Unit
Unconformity
A gap or missing layer in a rock column
Superposition
A principle that states that younger rocks lie above older rocks if the layers have not been disturbed
Relative Age
An object or event being older or younger than another
Era
Shorter than an eon, longer than a period
Period
Shorter than an era, longer than an epoch
Epoch
Smallest unit of geologic time
4.6 billion years
The estimated age of Earth and the solar system
Correlation
The matching of rock layers from different areas in terms of age
Geologic Time Scale
Broken into eons, eras, periods, and epochs
Fossil
Evidence of past life; most commonly preserved in sedimentary rock
Eon
Largest unit of geologic time
Index fossil
Must come from a species that existed for a short period of time
Older
rocks on the bottom of a rock column
Younger
rocks on the top of a rock column
Precambrian
the name of the era that accounts for about 90% of Earth's history