Describe Earth's formation.

Describe Earth's formation.

• A. Earth formed as a fragment of an existing planet with no core-silicate differentiation.
• B. Earth formed from a rotating disk of gas and dust around the young Sun, with heavier elements forming the core and lighter silicates forming the crust.
• C. Earth formed from a single chunk of rock with no differentiation.
• D. Earth formed by direct condensation of water to create oceans first.

Answer: (B)

Planets grow from a rotating disk of gas and dust around the young Sun. As material accretes, the growing Earth heats up from impacts and radioactive decay. This heat allows iron and other dense metals to melt and sink toward the center, forming a metallic core, while the lighter silicate materials rise to form the mantle and crust. This internal differentiation creates Earth’s layered structure: a dense core beneath a silicate outer shell. Later cooling solidifies the crust, and volatiles delivered by late accretion help form oceans and the atmosphere. This aligns with evidence that Earth experienced an early molten state and developed a differentiated interior. The idea of Earth as a fragment of another planet with no differentiation contradicts the observed layered structure. The notion of a single, undifferentiated chunk also clashes with the heating and melting that differentiation requires. And oceans forming first from direct water condensation wouldn’t account for how water is delivered and retained until after the planet cooled and volatile-rich material accumulated.

Planets grow from a rotating disk of gas and dust around the young Sun. As material accretes, the growing Earth heats up from impacts and radioactive decay. This heat allows iron and other dense metals to melt and sink toward the center, forming a metallic core, while the lighter silicate materials rise to form the mantle and crust. This internal differentiation creates Earth’s layered structure: a dense core beneath a silicate outer shell. Later cooling solidifies the crust, and volatiles delivered by late accretion help form oceans and the atmosphere.

This aligns with evidence that Earth experienced an early molten state and developed a differentiated interior. The idea of Earth as a fragment of another planet with no differentiation contradicts the observed layered structure. The notion of a single, undifferentiated chunk also clashes with the heating and melting that differentiation requires. And oceans forming first from direct water condensation wouldn’t account for how water is delivered and retained until after the planet cooled and volatile-rich material accumulated.