When a rock is exposed to weather, it begins a process called weathering. This process breaks down the rock into smaller pieces and changes its composition. Here's how weathering happens:

Physical Weathering:

* Frost Wedging: Water seeps into cracks in the rock, freezes and expands, putting pressure on the rock. This repeated freezing and thawing can eventually cause the rock to break apart.

* Thermal Expansion and Contraction: Rocks expand when heated and contract when cooled. If this happens repeatedly, the rock can weaken and crack.

* Abrasion: Rocks can be worn down by the friction of other rocks, sand, or even wind. This is common in deserts and along coastlines.

* Root Wedging: Tree roots can grow into cracks in rocks and exert pressure, breaking the rock apart.

Chemical Weathering:

* Oxidation: This happens when iron in the rock reacts with oxygen, creating rust which weakens the rock.

* Dissolution: Acidic rainwater can dissolve certain types of rocks like limestone.

* Hydrolysis: Water reacts with minerals in the rock, changing their composition and weakening the rock.

* Biological Weathering: Living organisms like lichens, bacteria, and plants can release acids that break down rocks.

The overall effect of weathering:

* Breakdown of rocks: Weathering breaks rocks into smaller pieces, creating sediment that can be transported by wind and water.

* Soil formation: Weathering plays a crucial role in the formation of soil, which is essential for plant life.

* Landform development: Weathering can shape landscapes, creating canyons, valleys, and other geological features.

So, in short, a rock exposed to weather begins to break down, change its composition, and contribute to the formation of soil and the evolution of landforms.