Evolution of Earth’s Layered Structure
Earth has a layered structure, having an outer rocky crust and mantle overlying a molten and solid metal core, however, this internal layered arrangement did not exist early in Earth's history (Figure 1.85).
• Early in Earth's history the composition of the planet was probably more homogeneous. However, just like oil and water don't mix, metals separated from non-metal substances, and as metals are denser, gravitation forced them to sink toward the planet's core.
• Likewise, molten material rich in dissolved gases and lighter silica-rich matter is less dense and over time it gradually migrated upward accumulating in the mantle and thin crust where some of it reached the surface, resulting in volcanism and massive degassing.
• Despite intense asteroid bombardment, early crust began to form.
• Chemical segregation under the influence of gravity established the basic divisions of Earth’s interior (core, mantle, and crust). This process also happened with other planets, moons, and planetesimals in the Solar System.
Figure 1.85. Formation of the early Earth and the eventual development of its internal layered structure: core, mantle, and crust. Volcanic degassing and accumulating gases from space led to the formation of Earth's atmosphere and oceans.