Cosmic Origin

#before-4bya

~13.8 — 13.4 BYA

Atoms

• Atoms (recombination): ~13.7996 BYA

Cosmic Dark Ages

• Cosmic Dark Ages: ~13.8 to ~13.6 BYA

First Stars

• First stars form: ~13.6–13.7 BYA

~13.4 — 12 BYA

First Large-Scale Structure

• Ignition of First stars (Pop III): Population III stars remain theoretically unobserved despite strong indirect evidence.
• Reionization begins: the ultraviolet light from early stars ionizes hydrogen.
• First galaxies:  Form from dark matter halos.

~12 — 8 BYA

Galaxies

• Galaxies grow: Through mergers and star formation.
• First generations of stars: Synthesis of heavy elements (carbon, oxygen, iron) via nuclear fusion and supernovae.

Heavy Elements

• Heavy elements: Seed future planetary systems.
• The Milky Way: Forms and evolves during this period.

~8 — 4.6 BYA

Galactic Stabilization

• Star formation rate: Peaks and then declines.
• Spiral galaxies (like the Milky Way): Develop stable structures.
• Multiple generations of stars: Enriched interstellar space with metals. Conditions for rocky planets become common.

~4.6 — 4.54 BYA

Solar System

• Solar system forms: ~4.57 BYA → A region of the Milky Way collapses into a protoplanetary disk. The Sun ignites at the center. Planets, moons, asteroids, and comets form from remaining material.

Earth

• Earth forms: ~4.54 BYA