Saturday, November 29, 2014

Climate Change Part 11 Where Oil comes from Part 1

Note: This program first aired on November 22, 2014.

At last! A return to the Climate Change Series!!
It’s been many weeks, even months since we last talked about climate change, but I haven’t forgotten that I never finished that series. Today we start to rectify that. When last I looked at climate change, we were talking about the formation of the massive coal beds that fueled the beginning of the industrial revolution. Coal is still big business and a significant environmental issue today, especially in electricity production, air quality and destructive mining practices. Coal has been surpassed by oil in both the popular imagination and in the carbon dioxide emissions data as the number one climate change villain, and it is to oil that we turn today.

Where does oil come from? It doesn’t have its own neat and tidy geologic era like coal does, and the processes that form oil are still going on today. People have been arguing about the origins of oil since we discovered it. One camp holds that oil forms abiotically, meaning it can form from inorganic sources of carbon in the absence of life. The other posits that oil is formed biotically, from carbon found in once living organisms. It turns out both theories are correct, though one explains the vast commercial deposits of oil we exploit better than the other. Hydrocarbons can be created inorganically, that’s how Saturn’s moon Titan can have lakes filled with liquid methane on its surface, or meteorites can contain organic carbonaceous materials. The vast majority of hydrocarbons here on Earth though, are formed through biotic processes.

When oil is found in large deposits, it is always found in sedimentary rock that is marine in origin. Whether it is a sedimentary deposit that is still under water, or a much more ancient deposit that is now far inland, that rock deposit originated as terrestrial sediment that was washed into the ocean and deposited along the coastal margins of the continental shelf and continental slope. Its what gets buried along with that sediment that makes up the oil that we burn so freely today. And for that we need to talk about productivity.

Virtually all energy that flows through living organisms and biotic systems originates from the sun. This is true for your breakfast, its true for your dog food, its true for the gas in your car. The sun’s energy comes to Earth in the form of light, in your breakfast, dog food and gasoline, it has been transformed into chemical energy. Plants are the means by which that energy gets changed from wavelengths of light to chemical bonds, a process we all know as photosynthesis. Plants absorb light energy and rearrange the bonds of water and carbon dioxide. They form new molecules from those atomic ingredients, and in the bonds of the new molecule, aka glucose, the sun’s energy is stored chemically. Ecologically this is known as primary productivity. The more primary productivity going on, the more energy is entering an ecosystem. 

In the ocean primary productivity is limited by two factors; light and nutrient availability. At the surface of the ocean there is usually plenty of light, so what tends to limit productivity in most parts of the ocean is nutrient availability. When we say nutrients, we mean the same kinds of things that plants everywhere need: nitrogen, phosphorous, potassium, iron and a wide range of other minerals in very small amounts. Nutrients are quite limited at the surface of the ocean in most regions, so while there can be plenty of light to drive productivity, if there are no nutrients, there is no action. The coastal ocean however has access to nutrients that the rest of the ocean does not. These nutrients come to coastal waters through run off from land, sediment washing from land to water in a constant and inevitable flow. If you look at a map of global sea surface chlorophyll levels, chlorophyll, as the photosynthetic pigment in plankton is a proxy for primary productivity, the pattern is clear. Productivity along coastlines is high on virtually every shoreline world wide. What this has to do with the formation of oil, you’ll have to wait until next week to find out.


From the GRID Arendal Center in collaboration with United Nations Environment Programme, figures on the proportions of Carbon Dioxide from oil, coal and natural gas:

From the Louisiana Department of Natural Resources: