Here's why:
* R Horizon: This is the bedrock layer, the unweathered parent material from which soil forms. It's the foundation upon which the entire soil profile sits.
* Weathering: The process of weathering is the breakdown of rocks, minerals, and other materials at the Earth's surface. It's a gradual process that happens over time due to factors like:
* Physical Weathering: Caused by forces like temperature changes, freezing/thawing, and abrasion.
* Chemical Weathering: Caused by reactions with water, acids, or oxygen.
* Biological Weathering: Caused by organisms like plants, animals, and bacteria.
How it Works:
1. Exposure: As the top layers of soil erode, the bedrock (R horizon) becomes exposed to the elements.
2. Weathering Begins: Weathering processes start to break down the solid rock, gradually creating fragments and particles.
3. Soil Formation: These weathered particles, mixed with organic matter and other materials, become the foundation for the development of the soil profile above.
Important Note: Weathering doesn't just happen at the very bottom. It can also occur in other parts of the soil profile, particularly in the deeper layers where the parent material is still relatively fresh. However, the R horizon is where the bedrock is directly undergoing weathering.
