There's a lot of talk about fossil fuels when people speak about climate and how it changes. For now, set aside whether or not these fuels increase the global average temperature. What are "fossil fuels"?
Fossil fuels include methane, propane, oil, coal--what are referred to as hydrocarbons. They have only C (carbon) and H (hydrogen) atoms. The simplest is methane, CH4, also called natural gas. Ethane (C2H6), propane (C3H8 ) and butane (C4H10) are all common hydrocarbons used for things like home heating, butane lighters, etc.
In addition to methane and it's relatives, there's oil and coal. These are not pure hydrocarbons. Crude oil is not like gasoline or home heating oil--crude oil has various compounds mixed in, sometimes metals. Crude oil is distilled into various compounds, including gasoline, in a refinery. This is a multistep process.
In the past, and probably some schools now, children were taught oil came from dead dinosaurs that were covered by rock and dirt and then crushed by soil or rock. Sinclair Oil has a dinosaur trademark, which adds to the belief. Today, the belief is oil was created from zooplankton, algae and dead plant matter on the bottom of lakes and the ocean. This material was then buried under sediment, creating an environment without oxygen. If oxygen were present, microbes could break down the organic matter. Over time, heat and pressure break down the organic compounds and produce kerogen--a waxy solid that then is further heated and compressed by the earth, resulting in liquid crude oil. This process can be shown to work in a lab--kerogen to oil via heat and pressure. Once a liquid, the hydrocarbon cannot return to the solid state.
The theory of algae and zooplankton forming oil is called "biotic" formation. While we call it "fossil fuel", there are not fossils involved, just organic matter trapped on a lake bottom. There is another theory of oil formation called "abiotic formation" that holds that oil is not formed from dead organic matter but rather formed deep within the mantle of the earth. Pressure and heat compress substances that are transformed to liquid hydrocarbons. This liquid, crude oil, migrates through the mantel and is trapped in impermeable strata. One piece of evidence cited for the abiotic theory is that oil and gas wells will regenerate after a while, allowing us to get more oil from a "spent" well. Much of the support for the abiotic theory is found in Russia and the Ukraine, though there were theories about abiotic oil dating back to the 16th century and the 19th century.
We do know methane can be created abiotically. It's found on Saturn's moon Titan in large quantities, along with other hydrocarbons. No dead organic material would have been available for the formation of the methane. Methane is also also formed in landfills as the buried material decomposes. Currently, there's no reliable, economical way to recover this gas (some have tried but the expense was large).
Even if the oil supply is diminished, there remains methane from various sources that can be used for heating and generating electricity.
Which theory is correct? No one knows. Oil formed long before there were humans to observe how it happened. It's possible that both theories are correct and oil comes both from organic matter and from deep in the earth's mantle.
Why is this importunate? One of the worries with oil, ignoring any CO2 factors, is what is called "peak oil". Peak oil is the point at which humans reach the maximum available oil and the supply then decreases rapidly over a short period. In other words, we will need more oil than we can find and recover. If the biotic theory is correct, oil is no longer being formed (although it is possible for oil to still be forming under the oceans and in areas where there were lakes, etc, since we don't know that all formation of oil ended in the past. It is likely that new oil would not form fast enough for our needs even if this is happening.) If oil is abiotic, then it is constantly forming and moving toward the surface of the earth. If it's both processes, then there is likely far more oil than we estimated and our supply is secure for many years (if not centuries). The biotic theory has the most evidence at this point. However, in the last 10 to 20 years, huge reserves of oil and natural gas have been found. No one really has a firm idea of how much oil is out there nor when it will peak, if ever.
|Work over rig|
|Drill rig (at dusk)|