Weathering breaks rocks down into smaller pieces over time through mechanical, chemical, and biological processes. Mechanical weathering is caused by temperature changes that make rocks expand and contract, cracking them. Water freezing in these cracks also breaks rocks apart. Chemical weathering occurs as rainwater reacts with minerals in rocks. Biological weathering results from plant roots and small creatures breaking up rocks to make space in cracks. All of these types of weathering break rocks into smaller pieces that eventually become soil.