Geological Time Scale
Introduction
The geological time scale is a system of chronological measurement that relates stratigraphy to time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history.
Principles of the Geological Time Scale
The geological time scale is based on the Principle of Original Horizontality, the Principle of Superposition, the Principle of Cross-Cutting Relationships, and the Principle of Faunal Succession. These principles allow geologists to determine the relative ages of rocks and features on Earth.
Divisions of the Geological Time Scale
The geological time scale is divided into several units of time. These divisions are, from largest to smallest: eons, eras, periods, epochs, and ages.
Eons
Eons are the largest division of the geological time scale. There are four eons in Earth's history: the Hadean, the Archean, the Proterozoic, and the Phanerozoic.
Eras
Eras are the second largest division of the geological time scale. Each eon is divided into several eras. For example, the Phanerozoic eon is divided into three eras: the Paleozoic, the Mesozoic, and the Cenozoic.
Periods
Periods are the third largest division of the geological time scale. Each era is divided into several periods. For example, the Mesozoic era is divided into three periods: the Triassic, the Jurassic, and the Cretaceous.
Epochs
Epochs are the fourth largest division of the geological time scale. Each period is divided into several epochs. For example, the Cretaceous period is divided into two epochs: the Early Cretaceous and the Late Cretaceous.
Ages
Ages are the smallest division of the geological time scale. Each epoch is divided into several ages. For example, the Late Cretaceous epoch is divided into six ages.
Dating Methods
There are two main types of dating methods used by geologists to determine the age of rocks: relative dating and absolute dating.
Relative Dating
Relative dating methods are used to determine the sequence of geological events. These methods are based on the principles of stratigraphy.
Absolute Dating
Absolute dating methods are used to determine the actual age of rocks. These methods are based on the decay of radioactive isotopes.
Importance of the Geological Time Scale
The geological time scale is an important tool used by Earth scientists to understand the history of our planet. It allows scientists to correlate events across different locations, to understand the evolution of life, and to study climate change over time.