 There are a number of different factors that influence the rate of weathering. One of the most important is water. And water is important for both the physical and chemical weathering. For physical weathering, having water go into the cracks and rocks, change phase or evaporate is really important. For chemical weathering, water facilitates the chemical reactions. So without water, chemical weathering doesn't occur. Another important thing is temperature. And for physical weathering, we talked about how the freeze-thaw cycling can enhance the breakage of rocks. For chemical weathering, it's really important because reactions are faster at higher temperature. So given the same rock type, the same water chemistry, a rock near the equator, where it's warm on average, will be much more quickly chemical weathered than one, say, in Antarctica. Another important component is the water chemistry. So a number of the reactions, for example, weathering, plagiclase, consume acidity. And so more acid water can cause a lot of weathering reactions to occur more quickly. And so this actually is really important in terms of plants. And so I'm going to put vegetation as a fourth key aspect of chemical weathering. And one aspect of that is the organic acids. So plants evolved to produce organic acids that helped break down rocks to make good soil and it releases nutrients in the rock and provides a good substratum for the vegetation to grow on. So the fact that vegetation often releases organic acids is an evolutionary response to the fact that acids help promote weathering processes. Another key component for vegetation is roots. So roots start out small and they grow bigger and the little root tips can go into small cracks in the rock and as they grow, they can break the rocks apart. And so the effect of roots is very important on the extent of weathering. So the chemical weathering depends very strongly on environmental conditions and biology. Thanks for watching.