Geological Timescale Divisions

Study Notes

Eon: The largest division of the geological timescale, with four eons: Hadean, Archean, Proterozoic, and Phanerozoic.
Era: A division of an eon, with multiple eras within each eon. Eras are characterized by significant geological or biological changes.
Period: A division of an era, with multiple periods within each era. Periods are characterized by specific rock formations or geological events.

Formation of the Earth: Approximately 4.5 billion years ago, the Earth formed through the accretion of dust and gas in the solar nebula.
Oxygenation of the Atmosphere: Around 2.7 billion years ago, oxygen-producing cyanobacteria emerged, changing the Earth's atmosphere.
Mass Extinctions: Five major mass extinctions have occurred, with the most recent being the Cretaceous-Paleogene extinction event that wiped out the dinosaurs.

Early Life: The first life forms, such as single-celled organisms, emerged around 3.5 billion years ago.
Cambrian Explosion: Around 541 million years ago, there was a rapid diversification of life forms, with the emergence of many animal phyla.
Dinosaurs: Dominated Earth's landscapes during the Mesozoic Era (252-66 million years ago), with over 1,000 known species.
Mammals: Emerged during the Paleocene Epoch (66-56 million years ago) and diversified during the Cenozoic Era.

The largest division of the geological timescale is the Eon, with four eons: Hadean ( earliest phase of Earth's history), Archean ( ancient era), Proterozoic (era of slow change), and Phanerozoic (era of visible life).
An Era is a division of an eon, characterized by significant geological or biological changes.
A Period is a division of an era, characterized by specific rock formations or geological events.

The Earth formed approximately 4.5 billion years ago through the accretion of dust and gas in the solar nebula.
Oxygen-producing cyanobacteria emerged around 2.7 billion years ago, changing the Earth's atmosphere.
There have been five major mass extinctions, with the most recent being the Cretaceous-Paleogene extinction event that wiped out the dinosaurs.

The first life forms, such as single-celled organisms, emerged around 3.5 billion years ago.
The Cambrian Explosion, around 541 million years ago, was a rapid diversification of life forms, with the emergence of many animal phyla.
Dinosaurs dominated Earth's landscapes during the Mesozoic Era (252-66 million years ago), with over 1,000 known species.
Mammals emerged during the Paleocene Epoch (66-56 million years ago) and diversified during the Cenozoic Era.