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.
References:
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:
Methane on Titan’s moon: http://www.space.com/16127-titan-tropical-lake-saturn-moon.html
