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