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4. Planetary Age
1. Event highlights
Accretion of Planetesimals
Following the solar nebula collapse, dust grains in the disk collided and stuck together via electrostatic forces and gravity to form "planetesimals." These kilometer-sized objects further coalesced to form the protoplanets of the inner and outer Solar System.
The T-Tauri Solar Wind
The young Sun entered a highly active "T-Tauri" phase, generating intense solar winds. This stream of charged particles swept away the remaining nebular gas and dust, halting the growth of the Jovian planets and stripping the primordial atmospheres from the inner planets.
Planetary Differentiation
Intense heat from accretion and radioactive decay caused the early Earth to melt. Heavy elements like iron and nickel sank to the center to form the metallic core (generating the magnetic field), while lighter silicates rose to form the mantle and crust.
Formation of the Moon
A Mars-sized protoplanet collided with the newly differentiated Earth. The debris from this cataclysmic impact formed a ring around Earth, which rapidly accreted to form the Moon.
Formation of Atmosphere and Oceans
As Earth cooled, volcanic activity outgassed volatiles (water vapor, carbon dioxide) from the interior to form a secondary atmosphere. As temperatures dropped further, this water vapor condensed to form the first oceans, augmented by water delivered by comets.
Late Heavy Bombardment
A period of intense asteroid and comet impacts scarred planetary surfaces and pulverized the early crust. This "cleaning up" of leftover solar system debris kept Earth's surface molten and hostile for millions of years.
Stabilization of the Lithosphere
The Planetary Age concluded with the stabilization of Earth's solid crust and the formation of the first continents (such as the Vaalbara supercontinent). This transformed Earth from a chaotic, molten "battlefield" into a stable environment capable of sustaining complex chemical evolution.