2.5 Geologic Timeline

The law of crosscutting states that a fault or intrusion is younger than the rocks it cuts through.

Precambrian Time is the earliest part of Earth's history, covering about 88% of geological time, and it precedes the Paleozoic Era.

The Earth formed approximately 4.6 billion years ago.

The law of superposition states that in undisturbed sedimentary rock layers, younger rocks lie above older rocks.

Trilobites are considered the oldest among these fossils.

Relative dating is a method used to determine the age of rocks and fossils in relation to one another, without assigning a specific numerical age.

An unconformity is a surface of contact between two groups of unconformable strata, indicating a gap in the geological record.

Absolute dating provides a specific age or date for a rock or fossil, while relative dating places events in order without exact dates.

Index fossils are fossils of organisms that were widespread but only existed for a short period of time, used to date and correlate the age of rock layers.

The Cenozoic Era is known as the 'Age of Mammals' and is significant for the evolution of mammals and birds after the extinction of the dinosaurs.