While its population accounts for 5% of people on Earth each year the US consumes about 20% of the worlds oil supplies and 12% of the worlds coal.
The US is a distant second in the production and consumption of coal behind China which uses approximately half of all the coal burned in the world.
In this lesson we will explain why, even though we have just a small proportion of the worlds oil and gas reserves we have recently become the worlds biggest oil and gas producer.
And why even though we have much of the worlds coal reserves, coal production in the US has been declining for the last decade.
We have three learning objectives for this lesson. First we will compare and contrast how fossil fuel such as oil, gas and coal are formed and where geologist would look to find these resources.
Next we'll explain how trends in the US fossil fuel production have gone in different directions in the last decade.
Before we begin, lets take a look at the principle forms of energy consumed each day in the US.
It turns out that we get energy from several sources with the three fossil fuels; petroleum, natural gas, and coal supplying more than 80% of our energy needs.
Most petroleum goes for transportation, while natural gas and coal are mainly used for electricity generation.
Fossil fuels, like coal, oil and natural gas, form from the remains of dead organisms over the course of millions of years.
These fuels are non-renewable in human lifetimes and once they are used up they can't be replaced.
In the next few panels we'll consider how these resources are created.
Oil and gas begin life as organic remains of tiny organisms such as algae or plankton living in the ocean.
Upon their death these micro-organisms increase the organic content of the sedimentary rock shale that is deposited on the seafloor.
In contrast, coal forms from organic matter on land. To form coal, you'll need a lot of vegetation that can be buried rapidly in warm, wet environments like tropical swamps before it can decay at Earths surface.
The organic rich shale is an essential first step in the formation of oil and gas. These organic materials experience increasing heat and pressure during burial to from kerogen.
With sufficient time and the right range of temperatures, kerogen is further converted to oil. If higher temperatures continue to cook the oil it will eventually be converted to natural gas.
Now that the oil and gas are formed, the next step is to have them migrate to a location where they can be retrieved.
More about that in a minute, lets first look at what happens as coal forms.
Coal deposits begin as spongy, peat with relatively low carbon content. As this plant matter gets buried and compacted, the carbon content will rise.
With more time and burial coal passes through several forms, from peat, to lignite to sub-bituminous coal and finally in some cases to anthracite.
More than 90% of US coal falls under bituminous or sub-bituminous coal types. Higher carbon coals generate more heat by burning a smaller volume of coal and producing less ash as waste.
The low density oil and gas escape from their source rocks and migrate upward through the overlying rock layers.
The hydrocarbons may be lost when they seep out at Earths surface or may be trapped in sedimentary rock below an impermeable cap rock unit.
Common types of structures that act as traps are folds, salt domes, faults and unconformities.
These reservoirs have good porosity and permeability, that allow them to hold large volumes of oil and gas and allow these reserves to easily travel to wells drilled into these structures.
Coal is much less mobile and is found in layers of various thicknesses among other sedimentary rocks. The nations coal reserves formed during times of warmer climates in the geologic past.
The older deposits found in states such as West Virginia, Pennsylvania and Illinois were formed during the late Paleozoic era when North America was part of Pangaea and closer to the equator.
These coals are often mined underground. Most US coal production comes from younger, less mature western coal deposits from states like Wyoming and Utah and formed around 50 million years ago.
And are more likely to be produced from surface mines. Unfortunately regardless of whether coal comes from the east or west coal is the dirtiest of fossil fuels and produces a higher proportion of carbon dioxide than other fossil fuels.
The US uses more oil than anyone else. Considerably more then it can produce so it is also the worlds largest oil importer. Most of that imported oil comes from Mexico and Canada.
US oil production increased steadily until the 1970's. Recent increases in oil and gas production are the result of technological innovations that allow these resources to be extracted from rocks that were previously considered unproductive.
This uptick in production and signaled a decrease in oil imports.
The US has the worlds greatest coal reserves however US coal production has declined in the last decade as power plants have favored using cleaner burning natural gas.
One consequence of this change is that the US carbon emissions have actually declined in recent years.
Examine the list of 16 items and identify which statements are true for oil only, for coal only or for both oil and coal.
Place these items in the appropriate location on the venn diagram.
Go ahead and pause the video while you complete this exercise.
Okay lets see how you did.
There are five statement each for the coal and oil circles and six more that are shared by both coal and oil that fall in the overlap area in the center of the diagram.
How did you do?
Here are the learning objectives for this lesson. How confident are you that you could complete these tasks?