eonsHadean

The eonsHadean, also called the Hadean eon, is the earliest eon in Earth’s history, spanning roughly from 4.6 billion to about 4.0 billion years ago. The name reflects a time when the planet was still forming and very little solid crust existed. The boundary with the preceding solar system formation and the subsequent Archean eon is defined largely by radiometric ages rather than a continuous rock record.

During the eonsHadean, Earth grew by accretion from the solar nebula and experienced intense internal heating. A major event, likely the collision with a large body now thought to be the Moon-forming impact, contributed to a predominantly molten surface or magma ocean. The surface environment was extreme, with widespread volcanism and frequent bombardment by planetesimals and comets. The atmospheric composition was dominated by volcanic gases such as water vapor, carbon dioxide, and nitrogen, with little or no free oxygen.

Evidence for what happened in this time comes mainly from fragile minerals that survived later conditions. Zircon crystals, some as old as about 4.4 to 4.3 billion years, indicate that liquid water and a differentiated crust may have existed earlier than previously thought. The eonsHadean leaves a world that was hot and largely reshaped by impacts, with the first stable crusts and oceans developing toward the end of the period.

By about 4.0 billion years ago, the Archean eon began, marking the transition to a more stable, cooler, and geologically active Earth. The eonsHadean thus set the stage for later crustal growth, ocean formation, and the eventual emergence of life.