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Scientists trace the birth of rocky planets like Earth to the accretion of dust and gas in the early solar system, which coalesced into hot, molten bodies billions of years ago. Once a planet emerged, it underwent four distinct phases—Differentiation, Cratering, Flooding, and Surface Evolution—that sculpted its present form.
Newly formed terrestrial planets go through four main stages: Differentiation, Cratering, Flooding, and Surface Evolution.
As a protoplanet grows, frequent impacts release immense heat, causing its interior to melt. Gravity then drives a separation of materials by density: heavy elements sink to form a dense core, while lighter silicates rise to create a crust and the earliest atmosphere. This process minimizes the planet’s gravitational energy, setting the foundation for its internal structure.
Once the surface cools, the relentless bombardment of planetesimals continues. Because the crust is solid, these impacts carve permanent craters. Early planetary bodies—such as Mercury and the Moon—display heavily cratered surfaces that have remained largely unchanged, providing a window into the violent youth of the solar system.
During the ongoing cratering phase, fractures in the crust allow molten rock to erupt, spreading vast lava flows that blanket the landscape and erase many impact scars. On Earth, water vapor also vented through fissures, condensing into rain that ultimately formed the first oceans—a phenomenon not seen on other terrestrial planets.
The final, protracted stage is shaped by tectonics, erosion, and atmospheric processes. Plate movements build mountains and shift continents, while weathering slowly smooths the surface, erasing the chaotic marks of earlier stages. Earth's internal heat, sustained by radioactive decay, has kept its interior dynamic, fostering conditions that allowed life to emerge.
