The Geosphere

The Geosphere

The Rock Cycle

The rock cycle
Credit: NESTA

The geosphere includes the rocks and minerals on Earth – from the molten rock and heavy metals in the deep interior of the planet to the sand on beaches and peaks of mountains. The geosphere also includes the abiotic (non-living) parts of soils, and the skeletons of animals that may become fossilized over geologic time.

Beyond these parts, the geosphere is about processes. The processes of the rock cycle such as metamorphism, melting and solidification, weathering, erosion, deposition, and burial are responsible for a constant recycling of rocks on Earth between sedimentary, igneous, and metamorphic states.

  • Sedimentary rocks are formed via weathering and transport of existing rocks, and then deposition, cementation, and compaction into a sedimentary rock.
  • Igneous rocks are formed by cooling and crystallization of molten rock.
  • Metamorphic rocks are formed when heat or pressure are applied to other rocks.

The primary agent driving these processes is the movement of Earth’s tectonic plates, which creates mountains, volcanoes, and ocean basins. Changes in the rate that rocks are made and destroyed can have a profound affect on the planet. As the rate of plate tectonic movements has changed over geologic time scales, the rock cycle has changed as well, and these changes have been able to affect climate. For example, at times when the rate of plate movements has been high, there is more volcanic activity, which releases more particles into the atmosphere. (See this week’s case study for more information about volcanoes and climate.) Faster plate tectonic movements also mean more mountains are built in areas where plates converge. As rocks are uplifted into mountains, they start to erode and dissolve, sending sediments and nutrients into waterways and impacting the ecosystems for living things.

As climate changes, the geosphere interacts with various other parts of the Earth system.

Biosphere: The carbon cycle, usually linked with the Earth’s biosphere, includes deep storage of carbon in the form of fossil fuels like coal, oil, and gas as well as carbonate rocks like limestone. The carbon cycle is one of several biogeochemical cycles, which all involve the geosphere, the biosphere, and other spheres of the Earth system.

Cryosphere: Glaciers and ice sheets, parts of the cryosphere, have a large impact on the rocks and sediments below them. For example, the continental ice sheet moved rocks as it flowed south during the last ice age, creating Cape Cod, Long Island, hills, and lakes. The ice is also able to have a regional affect on the elevation of land, which lifts up once ice has melted from its surface. The land in north central Canada has been slowly lifting up after the melt of glaciers from the last ice age.

Hydrosphere and Atmosphere: The erosion of rocks, a major part of the rock cycle and change in the geosphere over time, turns rock to sediment and then, sometimes, to sedimentary rock. But erosion, transportation, and deposition of sediments wouldn’t occur without the hydrosphere’s rivers, lakes, and ocean or the atmosphere’s winds and precipitation. Different combinations of sedimentary rocks form in environments with different climate conditions. This allows geologists to reconstruct what an environment was like millions of years ago based on the sedimentary rocks that were deposited.