Earth Structure

Introduction to Earth Structure

Earth is composed of several layers - the crust, mantle, outer core, and inner core - each unique in its properties and composition.
The transition from one layer to another is marked by abrupt changes in seismic velocities known as discontinuities.
The crust is Earth’s outermost layer, and it differs in thickness and composition between the oceanic and continental regions.
The mantle, beneath the crust, is the thickest layer and accounts for about 84% of Earth’s total volume.
The core, divided into the outer core and inner core, lies beneath the mantle and is primarily composed of iron and nickel.

Earth’s crust is subdivided into oceanic crust and continental crust based on differences in thickness and composition.
The oceanic crust, about 5-10 km thick, is generally denser and is mainly composed of basaltic rock.
The continental crust is considerably thicker, varying between 20-70 km, and mostly consists of granitic rock.
The crust is broken into a series of pieces called tectonic plates, and their movement over the partially molten upper mantle (asthenosphere) leads to seismic activity.

The mantle extends from the base of the crust to the outer core and is about 2,900 km thick.
It is subdivided into the upper mantle (including the asthenosphere), the transition zone, and the lower mantle.
The mantle consists mainly of ultramafic rock, peridotite, which is denser and darker than the crustal rocks.
The mantle’s upper most layer, the asthenosphere, has softer, partially molten rock which allows the rigid tectonic plates of the crust to move.

The core is divided into the outer core and inner core based on physical state.
The outer core, about 2,200 km thick, is mostly composed of liquid nickel and iron. The motion of this liquid generates Earth’s magnetic field.
The inner core, 1,250 km in radius, is solid despite its high temperature because of its extremely high pressure.
Knowledge about the core primarily comes from studying P-waves and S-waves (seismic waves) generated during earthquakes.

The investigation of Earth’s structure is possible due to the study of seismic waves generated by earthquakes and man-made explosions.
By studying the changing speed of seismic waves as they travel through Earth’s interior, scientists can draw inferences about different layers’ properties.
Earth’s structure study also contributes to our understanding of geological phenomena like volcanoes, earthquakes, and mountain building.
Studying Earth’s layered structure is fundamental for understanding plate tectonic theory, the thermodynamics of Earth’s interior, and earth’s magnetic field origin.