Fossil fuels are a non-renewable source of energy. This means that they cannot be replenished or replaced within a human lifespan, making them a finite resource that will eventually run out. Fossil fuels are formed over millions of years from the remains of plants and animals that lived and died long ago. They include coal, oil, and natural gas.

Non-renewable source of energy:

1. Limited availability: Fossil fuels are found deep underground, and their extraction requires significant effort and resources. Once these resources are depleted, they cannot be easily replenished.

2. Long formation process: Fossil fuels take millions of years to form, as layers of organic matter are subjected to heat and pressure. This slow process means that it is not possible to produce more fossil fuels within a human lifespan.

3. Environmental impact: The extraction, production, and use of fossil fuels have significant environmental consequences. Burning fossil fuels releases greenhouse gases, such as carbon dioxide, into the atmosphere, contributing to climate change. Additionally, the extraction of fossil fuels can lead to habitat destruction, air and water pollution, and other negative effects on ecosystems.

Renewable source of energy:

On the other hand, renewable sources of energy can be replenished or replaced within a human lifespan. These sources of energy are naturally replenished and do not deplete over time. Examples of renewable energy sources include solar power, wind power, hydropower, and geothermal energy.

1. Continuous availability: Renewable energy sources rely on natural processes that are ongoing, such as the sun's rays, wind currents, water cycles, or geothermal heat. As long as these processes continue, these energy sources will be available.

2. Lower environmental impact: Renewable energy sources have a lower environmental impact compared to fossil fuels. They do not produce greenhouse gas emissions during operation, reducing their contribution to climate change. Additionally, renewable energy sources do not require extensive extraction processes that can harm ecosystems.

In conclusion, fossil fuels are a non-renewable source of energy because they are limited in availability, take millions of years to form, and have significant environmental impacts. Renewable energy sources, on the other hand, can be replenished and have a lower environmental impact.