I know, right? It sounds much less exciting, but the process by which algae and other plant life soak up the Sun's energy, store it for millions of years, then give it all up for us to burn as fuel is a pretty fantastic tale!
Fossil fuel is a fuel formed by a natural process, the anaerobic decomposition of buried dead organisms who soaked up and stored energy from ancient photosynthesis. Picture ancient trees, algae and peat soaking up the sun, then storing that energy for us to use millions of years later. These organisms and their resulting fossil fuels are millions of years old, sometimes more than 650 million years. That's way back in the day when Earth's inhabitants were mostly viruses, bacteria and some early multi-cellular jelly-like critters.
Fossil fuels consist mainly of dead plants – coal from trees, and natural gas and oil from algae, a diverse group of aquatic photosynthetic eukaryotic organisms I like to think of as pond scum. These deposits are called fossil fuels because, like fossils, they are the remains of plants and animals that lived long ago.
If we could go back far enough, we'd find that our oil, gas, and coal deposits are really remnants of algal pools, peat bogs and ancient muddy swamps. Dead plants and algae accumulate and over time, then pressure turns the mud and dead plants into rock. Geologists call the once-living matter in the rock kerogen. If they haven't been cooked too badly, we call them fossils.
Kerogen is the solid, insoluble organic matter in sedimentary rocks and it is made from a mixture of ancient organic matter. A bit of this tree and that algae all mixed together to form a black, sticky, oily rock. The Earth’s internal heat cooks the kerogen. The hotter it gets, the faster it becomes oil, gas, or coal. If the heat continues after the oil is formed, all the oil turns to gas. The oil and gas then seep through cracks in the rocks. Much of it is lost. We find oil and gas today because some happened to become trapped in porous, sponge-like rock layers capped by non-porous rocks. We tap into these the way you might crack into a bottle of olive oil sealed with wax.
Fossil fuel experts call this arrangement a reservoir and places like Alberta, Iran and Qatar are full of them. A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. Petroleum reservoirs are broadly classified as conventional and unconventional reservoirs. In the case of conventional reservoirs, the naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability. In unconventional reservoirs, the rocks have high porosity and low permeability which keeps the hydrocarbons trapped in place, so these unconventional reservoirs don't need a rock cap.
Coal is an important form of fossil fuel. Much of the early geologic mapping of Canada (and other countries) was done for the sole purpose of mapping the coal seams. You can use it to heat your home, run a coal engine or sell it for cold hard cash. It's a dirty fuel, but for a very long time, most of our industries used it as the sole means of energy. But what is so bad about burning coal and other fossil fuels? Well, many things...
Dirty or no, coal is still pretty cool. It is wild to think that a lump of coal has the same number of atoms in it as the algae or rainforest that formed it. Yep, all the same atoms, just heated and pressurized over time. When you burn a lump of coal, the same number of atoms are released when those atoms dissipate as particles of soot. You may wonder what makes a rock burn. It's not intuitive that it would be possible, and yet there it is. Coal is combustible, meaning it is able to catch fire and burn. Coal is made up mostly from carbon with some hydrogen, sulphur (smells like rotting eggs, stinky pew), oxygen and nitrogen thrown in.
It is just that the long-ago rainforest was far less dense than the coal you hold in your hand today, and so is the soot into which it dissipates once burned. The energy was captured by the algal pool or rainforest by way of photosynthesis, then that same energy is released when the coal is burnt. So the energy captured in gravity and released billions of years later when the intrinsic gravity of the coal is dissipated by burning. It's enough to bend your brain.
The Sun loses mass all the time because of its process of fusion of atomic content and radiating that energy as light. Our ancient rainforests and algal pools on Earth captured some of it. So maybe our energy transformations between the Earth and the Sun could be seen more like ping-pong matches, with energy, as the ball, passing back and forth.
As mass sucks light in (hello, photosynthesis), it becomes denser, and as mass radiates light out (hello, heat from coal), it becomes less dense. Ying, yang and the beat goes on.
