The earth's geologic time scale is divided into [__] eons

What are the four eons? (w/ spaces)

From "Hades", Greek god of the underworld. Started with the formation of Earth through the collision of planetesimals.

In this eon:

- Differentiation of the different layers of the Earth.

- the formation of the Earth's magnetic field occurred during this eon.

From the Greek god "archaea" meaning old or ancient. In this eon:

- the Earth started to cooldown and form oceans 

- first continents appeared.

In this eon, deep-sea hydrothermal vents supplied heat and nutrients vital to support early life.

In this eon, unicellular prokaryotes became the dominant life form on Earth.

What showed that unicellular prokaryotes were the dominant life form on Earth?

The rise of cyanobacteria produced so much oxygen that free oxygen became present in the atmosphere and triggered The Great Oxidation Event.

This was triggered by the rise of cyanobacteria produced so much oxygen that free oxygen became present in the atmosphere. 

From "protero", meaning early, and "zoos" meaning life. First eukaryotes appeared in this eon.

Prokaryotes started living inside ancestral eukaryotes through endosymbiosis, producing mitochondria and chloroplasts as stated in The Endosymbiont Theory.

First multicellular organisms appeared in this eon during the Ediacaran period.

Periods in Paleozoic Era

Eras in the Phanerozoic Eon:

[____________] - a wide variety of complex life forms in all major animal phyla started to appear in the fossil record. Diversification of species.

Organisms developed hard calcium carbonate shells that fossilize.

The most widespread organism in this Period are the Trilobites.

This period was also know as the "Age of Invertebrates"

The earliest vertebrates were present in this eon.

In this period, after the melting of glaciers, coral reefs became widespread, aiding the evolution of fishes, both with and without jaws. (First jawed fish appeared)

Earliest vascular plants appeared on land as well as insects.

First insects appeared in this period.

This period was also known as the "Age of Fishes"

In this period, the rapid diversification of FISHES occurred, as well as the appearance of lobe-finned fishes which eventually became the first tetrapods.

A period in the Hadean eon where the atmosphere and ocean forms and where the oldest rocks formed as the earth cooled.

First land animals appeared in this period.

First AMPHIBIANS appeared.

The first REPTILES appeared in this period.

First LARGE CARTILAGENOUS fishes appeared in this period such as sharks.

The period where the plants that turned into coal came from.

This period is also known as "The Age of Amphibians"

This is the period when the PANGEA formed.

Three eras in the Phanerozoic Eon:

The second era of the Phanerozoic Eon.

The third era of the Phanerozoic Eon.

This is the period where the first dinosaurs appeared.

Periods during the Mesozoic Era.

The PANGEA cracked in this period.