Geologic Time, Topographic Maps
Unconformity
A gap or missing layer in a rock column
Contour line
A line on a topographic map connecting points with the same elevation
Topographic map
A map that shows elevation of the land
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
Contour interval
The difference in elevation between contour lines
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
Hachured line
Contour line that shows a dip or depression in the land
Index contour line
Every fifth contour line on a topographic map that shows the elevation
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
Highest possible elevation
One number less than what the next contour line's value would be
Gentle slope
When the contour lines are far apart
Steep slope
When the contour lines on a topographical map are close together
Older
rocks on the bottom of a rock column
Younger
rocks on the top of a rock column
Hilltop
shown by the smallest closed circles on a topographic map
Precambrian
the name of the era that accounts for about 90% of Earth's history