Which of the following best defines a nonrenewable resource?

The definition of a nonrenewable resource emphasizes its inability to be replaced once it has been consumed. This includes resources such as fossil fuels (like coal, oil, and natural gas) and minerals, which take millions of years to form and cannot regenerate on a human timescale. Once these materials are depleted, they cannot be replenished, leading to potential scarcity and environmental impact over time.

In contrast, the other definitions describe characteristics of renewable or sustainable resources. Renewable resources are those that can regenerate within a human timeframe, such as solar energy or timber when managed sustainably. Sustainable resources emphasize long-term maintenance of ecological balance without depletion. Resources that are readily available in nature may refer to both renewable and nonrenewable resources, but do not capture the essence of nonrenewability itself. Thus, the statement that a nonrenewable resource is one that cannot be replaced once used captures its fundamental nature accurately.