Lesson 2 - building a time line

This is a surface where the rock has eroded away, producing a break, or gap, in the rock record.

• unfonformity

• inconsistancy

• uniformity

• correlation

This is when geologists match rocks and fossils from separate locations.

• correlation

• key beds

• unconformity

• uniformity

These are species that existed on Earth for a short length of time (about 1-10 million years), were abundant, and inhabited many locations.

• index fossils

• key beds

• major geologic events

• unconformities

These are rocks or sediment layers that are used as a marker to correlate with other rock layers.

• key beds

• index fossils

• major geologic events

• unconformities

These leave behind evidence in rocks that geologists can use to determine relative age. Some examples include mountain ranges uplifting and eroding, oceans flooding the land and then retreating.

• major geologic events

• key beds

• index fossils

• unconformities

This is the model of Earth's history from its origin 4.6 billion years ago to the present.

• geologic time scale

• key beds

• index fossils

• major geologic events

These are the longest units of geologic time.

• eons

• era

• period

• epoch

These are the second longest units of geologic time. Eons are divided up into these.

• eras

• periods

• epochs

• unconformities

These are the third longest units of geologic time. Eras are divided up into these.

• periods

• eons

• epochs

• unconformities

These are the smallest main unit of geologic time. Periods are broken up into these.

• epochs

• eons

• eras

• unconformities