Which type of energy harnesses heat from decaying radioactive materials?

The correct answer is geothermal energy because it specifically involves harnessing heat that originates from the Earth, which includes heat produced by the decay of radioactive materials found deep within the Earth's crust. This decay process generates heat continuously over geological timescales, contributing to the geothermal gradient, which is the increase in temperature with depth beneath the Earth's surface.

Geothermal energy systems extract this natural heat, providing a sustainable and renewable energy source for electricity generation and direct heating applications. This heat can be accessed through geothermal power plants or through geothermal heat pumps, showcasing the practicality of utilizing the Earth’s internal thermal energy.

In contrast, wind energy relies on the kinetic energy of moving air, solar energy captures sunlight, and biomass energy originates from organic materials and their decomposition process. None of these options involve the specific process of harnessing heat from decaying radioactive materials like geothermal energy does.