One evolutionary event important for plants was the development of the atmosphere and oxygen and carbon dioxide since plants take in carbon dioxide and give off oxygen. The development of photosynthesis was key to taking advantage of this aiding in the ingestion of carbon dioxide and the respiration of oxygen. Also, the development of soil for plants to grow in is related to the evolution of landforms as for example the flooding of the banks of major rivers to deposit silt useful as a growing medium or the melting of glaciers forming glacio-fluvial soil deposits helped to provide such growing mediums. Natural selection also played a role in plant evolution so that varieties of each plant species developed and the varieties favorable to the environmental conditions would thrive. Also, biodiversity or the development of many types of plants adapted to their environment and to each other was very important to the development of say a rainforest or a tropical jungle.