Short answers, pulled from the story.
Sediment is the most abundant solid material on Earth and forms when rock is broken down by weathering and erosion. This loose collection of particles ranges from microscopic clay to massive boulders and is transported by wind, water, or ice to new locations. Over millions of years, this accumulation undergoes lithification to transform into sedimentary rocks.
The classification of sediment relies on a logarithmic scale known as the Phi scale which measures particle size from colloid to boulder. This system distinguishes between a boulder larger than 256 millimeters and a colloid smaller than 1 micrometer. The shape of these grains is defined by parameters such as sphericity, roundness, and surface texture.
Sediment moves across the landscape through three primary agents which are water, wind, and ice. Fluvial processes driven by rivers carry the majority of sediment while aeolian processes driven by wind transport fine sediments. Glacial processes move a wide range of sediment sizes from fine clay to massive boulders.
The marine environment serves as the ultimate destination for much of the Earth's sediment accumulating over time in various depositional environments. The continental shelf receives silty clays and increasing marine faunal content while the shelf slope holds much more fine-grained silts and clays. In the deep ocean the exoskeletons of dead organisms become the primary source of sediment accumulation.
Human activity has significantly altered the natural balance of sediment transport leading to severe environmental consequences. Slash and burn agriculture and shifting cultivation of tropical forests strip the ground of vegetation making the upper soils vulnerable to wind and water erosion. The cost of removing accumulated sediments due to water erosion alone is estimated to exceed 2.3 billion euro annually in the EU and UK.
Coastal development and sedimentation pose a critical threat to coral reefs which are vital ecosystems for marine biodiversity. Sediment can negatively affect corals by physically smothering them, abrading their surfaces, and causing them to expend energy during sediment removal. This process can also cause algal blooms that ultimately lead to less space on the seafloor where juvenile corals can settle.