Organic activity, with regards to weathering and erosion, is defined as the activity of plants and animals that cause physical weathering of landforms. This activity includes tree roots growing into crevices, lichens growing on rocks and animals burrowing into dirt.
Tree roots are strong enough to wedge apart rocks. When this happens on a cliff side or steep slope, the process can cause boulders to slide downward. Lichens cling to rocks and produce small amounts of acid. This acid eventually breaks down minerals and weaken stones, especially when thousands of lichens cover large areas. Burrowing animals loosen soil that washes away after heavy rain.
All of this organic activity is important because it helps weather rocks into soil over time. This soil produces viable ecosystems for more plants and animals. As new rocks rise to surface after tectonic movement, organic activity once again takes hold. In this way, Earth's natural geological processes assist life on the surface.
Weathering and erosion move large amounts of surface soil to different parts of the Earth. These deposits of soil, called sediments, allow plants to thrive. These plants provide food and shelter for animals. Organic activity is part of the overall balance of nature that keeps the Earth teeming with life.