Final answer:
The substructure expands out lower in the ground due to soil creep or solifluction, and also due to the systematic approach to building structures from the bottom up, as per the Aufbau Principle. Additionally, there is ongoing discussion about whether even smaller substructures exist beneath currently known particles.
Step-by-step explanation:
The substructure often expands out lower in the ground due to a natural process known as soil creep or solifluction. This occurs when moisture in the soil freezes during cold conditions, causing the ground to expand due to the ice expanding outwards at right angles to the slope. As temperatures rise and the soil thaws, it subsequently subsides vertically, which can create terraces on grassy slopes.
It's also worth noting that the building of structures, such as a house, requires a solid foundation. This is referred to using the Aufbau Principle, which suggests a systematic construction from the bottom up, similar to how atomic sublevels are arranged in increasing energy for electron configurations. Lastly, while discussing substructures, it's interesting to consider that as our understanding of matter deepens, we may discover more complex substructures beneath what we currently perceive as fundamental particles, much like atoms were once thought to be indivisible.