When rocks are subjected to weathering and erosion at the surface, they eventually become sedimentary rocks.

Here's why:

* Weathering: This breaks down the existing rock into smaller pieces, called sediment. This can happen through:

* Physical weathering: Freezing/thawing, abrasion, root wedging, etc.

* Chemical weathering: Acid rain, oxidation, etc.

* Erosion: This transports the weathered sediment away from its original location. Wind, water, and ice are common agents of erosion.

* Deposition: Eventually, the sediment comes to rest in a new location, often in layers.

* Lithification: Over time, the sediment is compacted and cemented together, forming sedimentary rock.

So, weathering and erosion are the first steps in the long process that turns existing rocks (igneous, metamorphic, or even other sedimentary rocks) into sedimentary rocks.