The geologic process most responsible for soil formation is weathering.

Here's why:

* Weathering breaks down parent rock: Weathering is the process of breaking down rocks, minerals, and other materials at the Earth's surface. It can be physical (like freezing/thawing or abrasion) or chemical (like oxidation or dissolution).

* Creates the foundation for soil: Weathering creates the small particles (sand, silt, clay) that make up soil. It also releases nutrients from the rock, making them available for plants.

* Other processes build on weathering: While weathering is the primary driver, other processes like erosion, deposition, and the activities of organisms (like earthworms and bacteria) contribute to soil formation.

So, while other processes are important, weathering is the fundamental geologic process that lays the foundation for soil.