Final answer:
Pebbles and sand can turn into a conglomerate, a sedimentary rock, through the processes of compaction and cementation. Compaction reduces the spaces between grains, while cementation binds them together with minerals like calcite, quartz, and pyrite that act as a natural glue.
Step-by-step explanation:
To turn pebbles and sand into a conglomerate, a type of sedimentary rock, two main processes must occur: compaction and cementation. During compaction, the porosity of the sediment, which is the empty space between grains, is reduced. This is similar to compressing garbage in a trash can to make more space. The weight and pressure of additional sediments on top cause the grains beneath to pack tightly together.
As compaction occurs, water is forced out of the pores. This water often contains dissolved minerals, which precipitate into the gaps. Cementation takes place when these minerals, like calcite, quartz, and pyrite, harden and act like a glue to bind the sediments into a solid rock.
Sediments may originate from the weathering and erosion of pre-existing rocks and are then transported by wind, water, or ice to a location where they can accumulate. Over time, with continued deposition and buried by additional layers, these sediments undergo the lithification process to become sedimentary rocks such as conglomerates, sandstones, and shales.