Energy was critical to industrializing economies. Waterpower was limited. Wood was never a very efficient fuel, as it gives off comparatively little heat: not enough to melt metals. In comparison, charcoal gives off twice as much heat as wood when burned. That left fossil fuels, which were abundant.
Humanity is rapidly extracting and burning fossil fuels without full understanding of the consequences. ~ American climatologist James Hansen
Fossil fuels are ancient organic matter protractedly pressed and heated via subterranean processes into various forms. Whereas coal comprises dead plants pressed into rock resemblance, petroleum originates from archaic algae and zooplankton, oozed into a viscous brew.
Coal came from the demise of mighty trees during the aptly named Carboniferous period (359–299 mya). It was an oxygen-rich time when insects grew to horror-movie size: foot-long cockroaches, dragonflies with meter-long wingspans, and gigantic spiders.
When the trees toppled, the stagnant swamps in which they grew protected them from rotting. Over millions of years the erstwhile trees dried, were compressed, and naturally cooked into coal.
Making crude oil is a more delicate process than crunching trees into coal. The dead bodies of tiny sea creatures had to have been trapped, preserved, and cooked at precisely the right pressures and temperatures. If the process went awry, the oil broke down into methane, also known as natural gas. Crude petroleum consists of several chemical components called fractions, which make for distinct products.
These fossils lay near the surface and within Earth’s crust for hundreds of millions of years; decayed organic remains transformed by pressure and heat into combustible hydrocarbons with rich energy content. Tapping that energy incurs considerable externality in polluting the air with particulates and greenhouse gases.
The hydrogen content of fossil fuels provides most of the energy. Much of the once-trapped carbon is released into the atmosphere, where it acts as a warming agent.