Final answer:
Fossil fuels are formed over millions of years from the remains of ancient plants and animals. The process includes decomposition, compaction, and heat-induced transformation. Due to the significant time required for their formation, they are considered non-renewable and measured in eons.
Step-by-step explanation:
Fossil fuels such as coal, petroleum, and natural gas are formed from the remains of ancient plants and animals. This process of formation is known to take millions of years due to the time-consuming steps it involves including decomposition, compaction, and heat-induced transformation. Hence, we infer that fossil fuels are made over millions of years. Given the substantial length of time required for their formation, they fall into the category of non-renewable resources. With respect to the time options provided – decades, centuries, millennia, and eons – the formation of fossil fuels is most appropriately measured in eons.
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