nd.gov - The Official Portal for North Dakota State Government
North Dakota: Legendary. Follow the trail of legends

Fossil Fuels

What petroleum and natural gas are:

A worker holds a small container of Bakken oil.
Bakken Oil: A worker holds a small container of Bakken oil. Photo courtesy of MBI Energy Services.
  • Petroleum is a flammable liquid mixture of hydrocarbons and other organic compounds found beneath the surface of the earth.
  • Petroleum is commonly called crude oil or oil.
  • Natural gas is a gaseous mixture of hydrocarbons, primarily methane, a colorless, odorless, flammable gas.
    • A hydrocarbon is a combination of hydrogen and carbon molecules.
  • Natural gas and petroleum are fossil fuels that are often found together. 
  • Natural gas is the cleanest-burning fossil fuel.
  • Petroleum and natural gas are fossil fuels. The other fossil fuel is coal. In North Dakota, oil and gas are found primarily in rocks that are 300 to 500 million years old. Lignite (a type of coal) in North Dakota is roughly 62 million years old. The North Dakota Geological Survey estimates that oil in the Bakken Formation began forming 70 million years ago.

How fossil fuels were formed:

  • Fossil fuels were created by anaerobic (without oxygen) decay of organic matter deep below the surface of the earth.
<span class='figure-reader-id'>Stage 1</span> During the Paleozoic (pay-lee-ah-ZOE-ik) Era, which lasted from about 540 million years ago to about 250 million years ago, land that included North Dakota was often covered by shallow seas. <span class='figure-reader-id'>Stage 2</span> Plant life grew along the edges of the seas, and the first forests appeared. The first four-legged animals also developed during this time. As algae, plankton and other organisms died, they accumulated in the sediment at the bottom of the sea. <span class='figure-reader-id'>Stage 3</span> Each time the seas would recede, decayed matter from the living things would be left behind. <span class='figure-reader-id'>Stage 3</span> Each time the seas would recede, decayed matter from the living things would be left behind. <span class='figure-reader-id'>Stage 3</span> Each time the seas would recede, decayed matter from the living things would be left behind. <span class='figure-reader-id'>Stage 3</span> Each time the seas would recede, decayed matter from the living things would be left behind. <span class='figure-reader-id'>Stage 4</span> Over millions of years, layer after layer of decayed plant and animal matter built up. <span class='figure-reader-id'>Stage 4</span> Over millions of years, layer after layer of decayed plant and animal matter built up. <span class='figure-reader-id'>Stage 5</span> Fast-flowing rivers carried and deposited sand, silt, and clay into the area. <br />These sediments were also piled into layers.<br />
<span class='figure-reader-id'>Stage 6</span> The pieces of sediment were pressed together and formed <strong>sedimentary rocks.</strong> <span class='figure-reader-id'>Stage 6</span> The pieces of sediment were pressed together and formed <strong>sedimentary rocks.</strong> <span class='figure-reader-id'>Stage 7</span> As decayed plants and animals became trapped in the sedimentary layers, heat and the weight of the sediments pressed them into material, which millions of years later transformed them into <strong>fossil fuels</strong> (petroleum, natural gas, and coal).
  
 
  • Petroleum and natural gas were created from miniscule aquatic organisms such as zooplankton and algae. (Coal primarily formed from plants that grew on land.)
    • The enormous weight and pressure, together with very high heat, “cooked” the marine organisms into the liquid called petroleum. As the heat increased, natural gas was created.