How do plants cause weathering of rocks?  

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Weathering of rocks, is simply, the breakdown of rocks by various factors. Plants are capable of weathering of rocks. In fact, plants can cause both mechanical and biological (or chemical) weathering of rocks. When plants grow on (or in vicinity of) rocks, their roots expand and go through cracks and fissures in the rocks. Over time, the roots grow in size and cause the crack to widen and eventually result in fragmentation and break down of the rock. This type of weathering (known as the mechanical weathering) will be even faster if the plant is larger in size. Plants are also capable of releasing molecules such as organic acids and chelating agents that break down the rocks and cause biological weathering. An example is lichen growing on rock surfaces.

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