What defines an aquifer?

An aquifer is defined as a natural underground layer capable of yielding water, typically consisting of permeable rock, sand, or gravel that can store and transmit groundwater. This characteristic allows aquifers to supply water for various uses, including drinking water and irrigation. The geology of an aquifer plays a crucial role in determining its ability to store and move water.

In contrast, the other options pertain to different concepts. While a layer of rock that stores oil relates to petroleum geology, it does not pertain to water storage. A body of water above ground is a lake or river, which is distinctly different from the geological structure of an aquifer. Lastly, a layer of sand that filters water could describe a component of an aquifer, but it does not capture the full definition, as aquifers can include various materials and are not limited to just sand. Thus, the defining feature of an aquifer is its capacity to yield water from an underground source.