Earth's Internal Structure: Lithosphere, Asthenosphere, and Core

Lithosphere and the Asthenosphere Paradigm

The crust and mantle form a rigid layer known as the lithosphere. This layer is fractured into lithospheric plates, which include:

• Oceanic Plates: Composed of basaltic oceanic crust.
• Continental Plates: Composed of granitic continental crust.

The Asthenosphere

The lithosphere is a rigid, fragmented layer consisting of large blocks moving at speeds of several centimeters per year. During the 1970s and 1980s, it was established that the asthenosphere acts as a continuous layer beneath the lithosphere, serving as a lubricant. Without this layer, the movement of the lithosphere would be impossible due to friction with the underlying mantle.

The Terrestrial Core

Heat generated by early planetary collisions and the decay of radioactive elements caused the planet to melt almost completely. This allowed dense iron to sink inward, creating a metallic core surrounded by a rocky mantle composed of peridotite.

Core Dynamics and Terrestrial Magnetism

The outer core is liquid, existing at temperatures over 3,000 degrees under a pressure of millions of atmospheres. Under these conditions, iron exhibits fluidity similar to water. Furthermore, the base of the outer core is approximately 1,000 degrees hotter than its upper portion. This significant temperature difference, coupled with its fluidity, produces violent convection currents.

Ionized iron separates positive and negative charges, which circulate along trajectories that generate a magnetic field. The Earth's rotation directs these convection flows, causing the magnetic poles to remain near the geographic poles. The study of paleomagnetism—the remanent magnetism of ancient rocks—reveals that the terrestrial magnetic field has weakened notably over time.

Earth's Internal Thermal Energy

The engine driving these processes is the Earth's internal thermal energy. The heat within the planet is almost entirely residual, originating from its formation 4.5 billion years ago through three primary processes: