The geosphere is the solid part of Earth, encompassing everything from its surface to its deepest interior. It is composed of various layers, each with distinct characteristics and compositions. Understanding the geosphere helps explain the planet’s dynamic processes and physical makeup.
Earth’s Outermost Layer
The Earth’s outermost layer is the crust, a thin, rigid shell. It varies in thickness, with continental crust ranging from 25 to 70 kilometers, and oceanic crust 5 to 10 kilometers. The crust is primarily composed of silicate minerals, with oxygen and silicon being the most abundant elements.
About 98% of its mass consists of eight main elements: oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. Common minerals include feldspar, quartz, and pyroxenes, forming igneous, sedimentary, and metamorphic rocks. The crust, despite being the thinnest layer, serves as the foundation for continents and ocean basins.
Beneath the Surface
Beneath the crust lies the Earth’s mantle, a thick layer extending approximately 2,900 kilometers deep. It makes up about 84% of Earth’s volume and 67% of its mass. This layer is predominantly solid rock but behaves like a viscous fluid over long geological timescales due to high temperatures and pressures. Its “plastic” nature allows for slow, continuous convective motion, where hot material rises and cooler material sinks. This convection drives tectonic plate movement on the surface.
The mantle is rich in silicate rocks, particularly those containing iron and magnesium. Oxygen, silicon, and magnesium are the most abundant elements, along with iron, aluminum, calcium, sodium, and potassium. Common minerals include olivine and pyroxene in the upper mantle, and bridgmanite and ferropericlase deeper due to pressure. Temperatures range from 700°C near the crust to 4,000°C near the core.
The Deepest Core
At Earth’s center, the core divides into a liquid outer core and a solid inner core. The outer core is a fluid layer about 2,260 kilometers thick, while the inner core is a solid sphere with a radius of approximately 1,220 kilometers. Both parts are primarily composed of iron and nickel, with trace amounts of sulfur, silicon, oxygen, and carbon in the outer core. Temperatures in the core range from 4,000°C to over 6,000°C, with high pressures keeping the inner core solid despite the heat.
The liquid outer core’s convective motion, driven by heat from the inner core, generates Earth’s magnetic field. This movement of molten iron and nickel creates electric currents, producing the planet’s magnetic field.