Earth's History

Age of rock compared to ages of other rocks.

• Relative Age

• Absolute Age

• Radioactive Dating

• Radioactive Decay

The number of years that have passed since the rock formed.

• Relative Age

• Absolute Age

• Radioactive Dating

• Radioactive Decay

The process of determining the age of an object using the half-life of one or more radioactive isotopes.

• Relative Age

• Absolute Age

• Radioactive Dating

• Radioactive Decay

A gap in the geologic record that shows where rock layers have been lost due to erosion

• Unconformity

• Fossil

• Radioactive Dating

• Radioactive Decay

The preserved remains or traces of an organism that lived in the past.

• Unconformity

• Fossil

• Radioactive Dating

• The Law of Superposition

In undisturbed horizontal sedimentary rock, the oldest is at the bottom and the newest the top.

• Unconformity

• The Law of Superposition

• Radioactive Dating

• Radioactive Decay

A record of the geologic events and the evolution of life forms as shown in the rock and fossil record.

• Geologic Time Scale

• Era

• Period

• Index Fossil

Geologists divide the time between the Precambrian and the present into 3 long units of time called..

• Geologic Time Scale

• Eras

• Period

• Index Fossil

Eras are subdivided into units of geologic time called...

• Geologic Time Scale

• Eras

• Periods

• Index Fossil

fossil that is useful for dating and correlating the rock layer in which it was found.

• Geologic Time Scale

• Eras

• Periods

• Index Fossil