After the Precambrian Era ended, the Paleozoic Era• Pronounced pay-le-a-zoe-ik
• From about 540 million years ago to about 248 million years ago
• Lasted about 292 million years
• Shallow seas came inland several times
• Water completely covered North Dakota
• First forests appeared
• First four-legged animals developed began. The Paleozoic Era lasted from about 540 million years ago to about 248 million years ago. During this time period of about 292 million years, shallow seas came inland several times. Sharks and other fish, along with many other kinds of animals, lived in the water. The water completely covered the area that we now call North Dakota and at times reached all the way from the Gulf of Mexico to the Arctic Ocean.
Vegetation (plant life) began growing along the edges of the seas, and in time, the first forests appeared. The first four-legged animals also developed during the Paleozoic Era.
Each time the seas would recede (go back), decayed matter from the living things would be left here. The plants and animals rotted and decayed, leaving layer after layer of matter. Fast-flowing rivers carried and deposited sand, silt, and clay into the area, and these sedimentsSmall pieces of rock and dirt carried by water or wind were also piled into layers.
Figure 4. The Williston Basin. (SHSND-ND Studies)
After many millions of years, the area which had been covered by the seas slowly filled up with sediments before the seas came again. These particles (pieces) of sediment were pressed together and formed sedimentary rocks.• Pronounced sed-a-men-ter-ee
• Rock formed by particles of sediment pressed together The region where these rocks accumulated is named the Williston Basin. The deepest part of the basin is near the city of Williston. The Williston Basin• Bowl-shaped region of sedimentary rock covering much of western North Dakota, as well as parts of South Dakota, Montana, Manitoba, and Saskatchewan
• Contains a lot of petroleum and natural gas covers much of western North Dakota, as well as parts of South Dakota, Montana, Manitoba, and Saskatchewan. (Manitoba and Saskatchewan are provinces in Canada.)
Rocks contain some of North Dakota’s major energy resources–oil, gas, and coal. The fuel we use today was formed from dead plants and animals which lived in the oceans and swamps that covered North Dakota millions of years ago.
As decayed plants and animals became trapped in the sedimentary layers, the weight of the sediments pressed them into material which millions of years later became fossil fuels.• Formed from the decayed remains of prehistoric (very ancient) plants and animals
• Petroleum, natural gas, and coal Petroleum (oil), coal, and natural gas are fossil fuels. They are called “fossil fuels” because they were formed from the fossilized remains of prehistoric (very ancient) plants and animals. The different types of fossil fuels were formed because of three factors: (1) the kinds of plants and animals and the areas where they lived; (2) how long they had been buried; and (3) the amount of heat and pressure they were exposed to as they were decomposing.
A fossil• Remains of a plant or animal that has been buried in the earth (in rock, soil, ice, etc.)
• Skeleton, bone, shell, or an imprint, such as a footprint is the remains of a plant or animal that has been buried in the earth (in rock, soil, ice, etc.). It could be a skeleton, bone, shell, or an imprint, such as a footprint.
Petroleum• Liquid fossil fuel created from tiny plants and animals that lived in oceans and had been squeezed by pressure for millions of year
• Formed during the Paleozoic Era and natural gas• Gas fossil fuel created from tiny plants and animals that lived in oceans; squeezed by pressure and exposed to heat for millions of years
• Formed during the Paleozoic Era were created from very tiny plants and animals that had lived in oceans. Hundreds to thousands of feet of earth continued to cover the dead plants and animals over the millions of years when the ancient seas kept advancing and receding. Even after the seas were gone, weight from the layers above continued to press down. This pressure squeezed the material into liquid that we call petroleum, and along with heat, formed natural gas. The Williston Basin contains a great deal of petroleum and natural gas, and today many oil wells are located in western North Dakota.
The type of coal found in North Dakota was formed in a similar way, with a few differences. This process will be explained later in the section on the Cenozoic Era because this coal was formed millions of years later than petroleum and natural gas.
Figure 5. Oil drilling rig in the western North Dakota Badlands. (Wyoming Casing Service)