Earth’s Geochemical and Dynamic Units: A Comprehensive Analysis
Geochemical Units
Geochemical units are defined by the composition of the chemical materials that make them up.
Crust
The crust is the outermost layer of the Earth, extending from the surface to the Mohorovičić discontinuity. There are major differences in thickness and composition between continental and oceanic crust.
1) Continental Crust
The continental crust ranges from 25 to 70 km in thickness. It is very heterogeneous, consisting of dense quartz rocks, feldspars, and micas. The lower half is dominated by metamorphic rocks such as gneiss and schists. Large clumps of granite are present, and the surface is covered with abundant sediments and sedimentary rocks. Continental crustal rocks range in age from 0 to 4000 Ma.
2) Oceanic Crust
The oceanic crust is much thinner, with a thickness between 5 and 10 km. It is stratified into three layers: a surface sediment layer, a basalt layer beneath it, and a gabbro layer, composed of feldspar and pyroxene. Oceanic crustal rocks are younger than continental rocks, with ages ranging from 0 to 180 Ma.
Mantle
The mantle is the zone between the Mohorovičić and Gutenberg discontinuities. It extends from the base of the crust to a depth of 2900 km. The most abundant elements in the mantle are O, Si, Mg, and Fe. It is primarily composed of peridotite. Density differences between the upper and lower mantle are due to pressure effects, which force the atoms to reorganize and form denser mineral structures.
Core
The core is the central area of the planet, located below the Gutenberg discontinuity. It represents 16% of the total volume of the Earth. Its high density, behavior when seismic waves pass through it, and its role in creating the magnetic field support the hypothesis that it is composed of iron and nickel.
Dynamic Units
Dynamic units are defined by the mechanical behavior of each terrestrial layer.
Lithosphere
The lithosphere is the outermost and rigid layer. It includes the entire crust and some of the upper mantle. Its thickness varies from place to place. Under the ocean, the oceanic lithosphere is 50 to 100 km thick, while the continental lithosphere is 100 to 200 km thick.
Sublithospheric Upper Mantle (Asthenosphere)
This layer is located below the lithosphere and extends to a depth of 670 km. The high pressures and temperatures cause the materials to behave differently depending on the time scale considered. The upper mantle beneath the lithosphere is called the asthenosphere, where mantle convection currents are thought to be limited.
Lower Mantle (Mesosphere)
The lower mantle includes the rest of the mantle, located between 670 km and 2900 km in depth. The rocks of the lower mantle are also subject to convection currents, caused by temperature and density differences between deeper and shallower areas. At the base of the mesosphere, bordering the core, is the D” layer, a discontinuous and irregular layer with a thickness from 0 to 300 km.
Outer Core
The outer core is located below the mantle, reaching a depth of 5150 km. It is liquid and characterized by convection currents, playing a key role in the creation of the Earth’s magnetic field.
Inner Core
As the core evacuates its heat through the mantle, iron crystallizes and accumulates in the center. This solid iron forms the inner core, which is increasing in size.