Structure of Earth's interior
Pro Research Analysisby 
Searched over 200M research papers
Earth's Interior Structure: Layers and Composition
The Earth's interior is organized into several distinct layers: the crust, mantle, outer core, and inner core. The crust is the outermost layer, varying in thickness from about 4 miles under the oceans to about 30 miles beneath mountains. The upper crust is mainly granite, while the lower crust and oceanic crust are primarily basaltic in composition. Beneath the crust lies the mantle, which is composed mostly of high-density oxides and silicates of silicon, iron, and magnesium. The core, which makes up the innermost part of the Earth, is predominantly iron, with the outer core being molten and the inner core solid. The core may also contain small amounts of lighter elements such as silicon, oxygen, sulfur, carbon, and hydrogen McQueen1964Ohtani2022Schulze2018.
Methods for Studying Earth's Interior: Seismic Waves and Gravity
Scientists study the Earth's interior using both indirect and direct methods. Indirect methods include analyzing the Earth's rotation, density, and mass, while direct methods rely heavily on seismic waves generated by earthquakes and artificial sources. Seismic data help identify the boundaries and properties of different layers, while gravity measurements provide insights into the behavior of the outermost layers Dercourt1933Poirier1991. Free oscillations of the Earth, observed after large earthquakes, also offer direct constraints on the density and composition of the deep interior .
Key Boundaries and Discontinuities in the Mantle
Within the mantle, there are important boundaries marked by changes in seismic velocity and density. The 410 km and 660 km discontinuities are caused by mineral phase transitions, such as the transformation of olivine to wadsleyite and the breakdown of ringwoodite into ferropericlase and bridgmanite. These transitions help define the upper and lower mantle. At the base of the lower mantle, the post-perovskite transition occurs, which may correspond to the D'' layer at the core-mantle boundary. Other notable features include Large Low Shear Velocity Provinces (LLSVP) and Ultra-Low Velocity Zones (ULVZ), which are thought to be regions of iron enrichment and possibly dense iron-rich melts .
Dynamics and Heat Transfer in the Earth's Interior
The structure and dynamics of the Earth's interior are shaped by its thermal regime. Heat is transferred from the deep interior to the surface mainly by convection in the mantle and core, with conduction occurring at boundary layers. Mantle convection drives plate tectonics, continental drift, and the movement of the lithosphere over the asthenosphere. The heat sources include residual heat from Earth's formation, radioactive decay of elements like potassium, uranium, and thorium, and latent heat from core solidification. Plumes rising from the lower mantle may bring material and heat to the surface, though they account for a small portion of the total heat loss today Pollack1991Teng2016Schulze2018.
Composition and Properties of the Core
The Earth's core is divided into a liquid outer core and a solid inner core. The outer core is responsible for generating Earth's magnetic field through the movement of molten iron. The inner core is mainly iron-nickel alloy, but its exact structure is still debated. It may consist of a mixture of different iron phases, such as hexagonal close-packed (hcp) and body-centered cubic (bcc) structures, which could explain observed seismic anisotropy and low shear velocities Dziewoński1987Masters1979Ohtani2022.
Conclusion
The Earth's interior is a complex, layered structure with distinct physical and chemical properties at each depth. Our understanding comes from a combination of seismic, gravitational, and mineralogical studies, revealing a dynamic system driven by heat and material movement. While much has been learned about the composition and behavior of the crust, mantle, and core, ongoing research continues to refine our knowledge of the deep Earth and its processes Pollack1991Dercourt1933McQueen1964+7 MORE.
Sources and full results
Most relevant research papers on this topic
Observational constraints on the chemical and thermal structure of the Earth's deep interior
The Earth's free oscillations constrain the density distribution, suggesting the outer core is not strongly chemically stratified but a thermally stable core cannot be excluded.
Introduction to the Physics of the Earth's Interior
This book provides a comprehensive introduction to the physics of the Earth's interior, covering fundamentals, melting laws, transport properties, and current seismological, thermal, and compositional models.
DOI