Final answer:
The energy converted by plants from sunlight during photosynthesis and stored in fossil fuels is a form of solar energy, not nuclear or geothermal energy.
Step-by-step explanation:
The conversion of light energy to chemical energy in photosynthesis ultimately results in the creation of fossil fuels over millions of years. This stored chemical energy is released when fossil fuels such as coal and petroleum are burned. The original source of this energy is solar energy, captured by plants through photosynthesis. Plants use solar energy to create glucose, which stores this energy in its chemical bonds. However, when plants die and are buried, over time, they may become fossil fuels, which can be categorized as an ancient form of biofuel.