only need a paragraph each

1. Fossil fuels have become a mainstay of global energy supply over the last 150 years. Why is the use of fossil fuels so widespread?

2. Fossil fuels present four challenges for long-term sustainability. What are they, and how do they compare in the severity of their impact and cost of their mitigation strategies?

3. The dominant global supply has changed from wood to coal to oil since the 1700s. How long did each of these energy transitions take to occur, and how long might a transition to alternate energy supplies require?