Earth system
Surface processes
The interior builds topography; the surface takes it apart again. Weathering and erosion are distinct processes, and treating them as synonyms hides why sediment ends up sorted.
Weathering is the breaking down of rock while it is in place, by biological, chemical and physical agents. Erosion is the movement of the fragments — six main agents, often acting together.[1, 2, 3, 4]
Transport sorts. Flowing water drops the largest particles first and finer ones as it slows, which is why the grain size of a sedimentary rock records the energy that delivered its material.[1, 2]
Deposition, burial, compaction and cementation close the loop into rock, joining the surface cycle to the rock cycle and, through subduction and spreading, to the tectonic engine.[1, 2, 3]
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Weathering, erosion and sedimentation
Weathering and erosion are routinely used as synonyms. They are not: one breaks rock down where it lies, the other moves the pieces. The distinction is the whole reason sediment ends up sorted.
The rock cycle
The rock cycle is usually drawn as a circle. It is better understood as a network: many possible pathways between materials, and no requirement that any particular rock travel the whole loop.
The chain
The processes in the order they act, from rock in place to rock again.
Geological process
Weathering
The breakdown of rock in place, by biological, chemical and physical means. It supplies the material that erosion later moves.
Geological process
Erosion
The movement of rock fragments away from where they were produced, by gravity, wind, rain, rivers, oceans and glaciers. Erosion transports; weathering merely breaks down.
Geological process
Sediment transport
The carriage of weathered and eroded material by wind, water or ice, during which particles are sorted by size and the largest are dropped first as the transporting medium loses energy.
Geological process
Deposition
The laying down of transported sediment where the carrying medium loses the energy to move it — or, for dissolved material, through evaporation and organic activity.
Geological process
Lithification
The conversion of loose sediment into rock through burial, compaction and cementation as pore water is expelled.
What it produces
The rocks that record each stage of the chain.
Rock
Conglomerate
A clastic sedimentary rock of rounded pebbles set in a finer matrix, recording transport energetic enough to move coarse material.
Rock
Sandstone
A clastic sedimentary rock made of sand-sized grains cemented together. Its grains are fragments of older rock, so a sandstone carries a record of a landscape that no longer exists.
Rock
Siltstone
A clastic sedimentary rock of silt-sized grains, intermediate between shale and sandstone in the grain-size classification.
Rock
Shale
A fine-grained clastic sedimentary rock made mostly of clay-sized particles, deposited where water was still enough for the finest material to settle.
Rock
Limestone
A carbonate sedimentary rock formed from the remains of organisms or by direct precipitation from water. Under metamorphism it recrystallises into marble.
What it consumes
Uplifted rock is what the surface system works on; erosion is the counterpart of orogeny.
Geological process
Orogeny
Mountain building. Not a single mechanism but a family of them: collision, subduction-related uplift, crustal shortening and thrusting, magmatic addition, and extensional fault-block uplift can each raise topography.
Earth layer
Continental crust
The thicker, less dense crust that makes up the continents. Its buoyancy is why continental lithosphere resists being drawn down at convergent boundaries, and why continental collision builds mountains instead of trenches.
Earth layer
Crust
The outermost compositional layer of the Earth: thin, rigid and brittle compared with the layers beneath it, and markedly thinner under the oceans than under the continents.
Hub last updated 2026-09-06. Every entry above is a structured record; the bracketed references link to the entities whose claims support each statement.