ProtoEarth

ProtoEarth refers to the early state of the planet that later became the modern Earth, existing roughly from the time of Earth's accretion until the complete differentiation of its core and mantle. This period spans from about 4.6 billion years ago to roughly 4.4 billion years ago, when the planet had not yet settled into the layered structure observed today.

During the protoEarth phase, the planet was primarily a molten, convecting body formed by the coalescence of planetesimals in the solar nebula. Short-lived radionuclides such as aluminium‑26 and iron‑60 produced intense heat, supporting widespread melting of iron and silicate materials. The high temperatures allowed the metallic iron to migrate toward the center, creating an early core, while melt‑rich silicates formed a proto-mantle that slowly cooled.

The protoEarth's atmosphere was likely vaporous and dominated by volatiles released from interior degassing, including water vapor, carbon dioxide, and sulfur compounds. This volatile inventory set the stage for the later development of a stable, oxygen‑free atmosphere. Periodic large‑scale impacts, particularly the theorized Moon‑forming event, further influenced the planet’s thermal budget and contributed to the accretion of crustal materials.

Understanding the protoEarth is crucial for planetary science because it provides insight into the processes of planetary differentiation, core formation, and the early evolution of Earth's surface and atmosphere. Its study relies on geochemical evidence from meteorites, isotopic dating, and numerical simulations of early solar system dynamics.