Explanation: the mining of copper and extraction of crude oil will sooner or later lead to their exhaustion and may take millions or thousands of years for them to replenish.
Coal is also non-renewable and it is a dirty source of energy. The reason why people reduced the consumption coal and sorted out new sources of energy is because they knew it will soon be exhausted.
The answer is wave energy and it is the main form of sea energy. We all know the sea won't run dry. The sea level might decrease or increase but never dry.
A chemical change has occurred because the wood has turned into a substance that can't be changed back to it's original form. The wood has turned to ash, chemical changes are non reversible.
