Which material moved toward the centre to form layers in the early Earth?

Correct answer: Denser, heavier materials

As the young Earth became sufficiently hot and partly molten, gravitational differentiation separated materials according to density. Dense elements and minerals, especially iron and nickel, sank toward the centre and contributed to the formation of the core. Less-dense silicate materials moved upward and formed the mantle and crust. This process explains why Earth developed concentric layers rather than remaining a uniform body. Option A is correct because gravity causes denser material to sink and lighter material to rise or remain nearer the surface. Light gases alone could not form the metallic core, while ice pieces and plant remains are not plausible materials for the formation of Earth’s internal layers.