Archean

The Archean Eon spans from 4.0 billion to 2.5 billion years ago, representing the era when Earth's crust cooled sufficiently for continents to begin forming. The planet looked vastly different than today, featuring a faint young sun, a toxic atmosphere lacking free oxygen, and high volcanic activity. Despite these harsh, volatile conditions, the Archean is monumental because it marks the definitive origin of life on Earth. The earliest fossil evidence, found in ancient rock formations like stromatolites, reveals that simple, single-celled microscopic organisms - specifically anaerobic bacteria and archaea - thrived in the primitive oceans. Geologically, the high heat flow from the Earth's interior drove rapid tectonic activity, creating small proto-continents that gradually collided to form larger landmasses. The end of the Archean set the stage for the oxygenation of the planet.