Geochemical cycle

A geochemical cycle is a complex pathway for chemical elements. These elements move through the Earth's crust and surface. This process allows chemicals to interact with various reservoirs. A reservoir is a place where chemicals are stored for a time. These cycles involve both geological and chemical factors. They move elements like silicon and aluminium through the planet. They also move general alkali metals. Over very long periods, these cycles cause massive changes. They help drive the evolution of our oceans and continents.

To understand these cycles, we must look at the Earth system. Earth is an open system regarding radiation from the sun. However, it is practically closed when it comes to matter. This means Earth follows the law of conservation of mass. This law states that matter cannot be created or destroyed. Instead, matter is only transformed or migrated. The same matter remains on Earth as it was when the planet formed. The system contains seven different reservoirs. These include the atmosphere, hydrosphere, biosphere, pedosphere, and lithosphere. The deep Earth and outer space are considered isolated reservoirs.

Geochemical cycles focus on specific interactions within the Earth. They occur between the deep Earth and the lithosphere. The deep Earth consists of the mantle and the core. The lithosphere is the Earth's outer crust. Scientists often distinguish these from biogeochemical cycles. Biogeochemical cycles involve the atmosphere, hydrosphere, lithosphere, and biosphere. While some use the terms interchangeably, they refer to different reservoirs. Geochemical cycles specifically deal with crustal and sub-crustal reservoirs. This distinction helps scientists track how elements move deep underground.

There are two primary pathways for material flux. Flux is the movement of material between reservoirs. One pathway is subduction, which occurs at convergent boundaries. This happens when one tectonic plate moves under another plate. The plate sinks deep into the mantle. This sinking process creates many geochemical transformations. These changes help cycle elements back into the deep Earth. This is a vital part of the planet's internal movement.

The second major pathway is volcanism. This process occurs at divergent boundaries. At these boundaries, one tectonic plate separates from another. This separation creates a rift in the crust. Molten rock, known as magma, erupts through this rift. This magma travels from the deep Earth toward the surface. This movement is a key way that elements are redistributed. It connects the deep mantle to the surface reservoirs.

Volcanism also leads to the creation of new rocks. When magma reaches the surface, it cools and crystallizes. This process forms igneous rocks. We categorize these rocks based on where they form. If crystallization happens at the surface, they are extrusive igneous rocks. If crystallization happens within the lithosphere, they are intrusive igneous rocks. Intrusive rocks can eventually reach the surface through denudation. This cycle of melting, cooling, and moving is constant.

These cycles involve the natural separation and concentration of elements. They also include heat-assisted recombination processes. These processes allow elements to bond in new ways. Because these changes happen over such long timescales, they are hard to see. We cannot easily notice them in our daily lives. However, they are responsible for the very structure of our world. They ensure that the chemical building blocks of Earth are always in motion.