The geological calendar is divided into four time periods called eras.
The Precambrian Era lasted about 4 billion years.
The Paleozoic Era lasted about 292 million years.
The Mesozoic Era lasted about 183 million years.
The Cenozoic Era has lasted about 65 million years, and we are still in this era now.
The Cenozoic Era is divided into the Tertiary and Quaternary Periods. (We are in the Quaternary Period of the Cenozoic Era.)
Petroleum, coal, and natural gas are called fossil fuels because they were formed from the fossilized remains of plants or animals.
The Mesozoic Era has been called the “Age of Reptiles.” Dinosaurs lived during the Mesozoic Era.
Fossils from more than a dozen different kinds of dinosaurs have been found in North Dakota.
The most common dinosaur found in North Dakota was Triceratops. It could weigh five tons.
Tyrannosaurus rex could weigh six tons, but its arms were only about three feet long.
Tyrannosaurus rex could eat 500 pounds of meat in one bite.
No person has ever seen a dinosaur because they were all extinct before humans lived on the earth.
North Dakota was once a hot area with palm trees and tropical flowers.
North Dakota once had thick forests with giant trees such as redwoods and sequoias.
Ancient trees and other plants became coal.
The kind of coal formed in North Dakota is called “lignite.”
The earth was probably struck by an asteroid 65 million years ago, killing most animals and plants.
The Cenozoic Era has been called the “Age of Mammals.”
Petrified wood looks exactly like the plant that had been there in the first place, except it is stone.
Western North Dakota has “petrified forests” that contain petrified stumps and logs.
The Quaternary Period of the Cenozoic Era has been called the “Ice Age.”
Glaciers covered North Dakota more than 20 times.
The Wisconsinan glacier was the last glacier to move over North Dakota and stayed here for about 28,000 years.
The Wisconsinan glacier covered all of North Dakota except for the southwest corner.
Lake Agassiz was formed because glaciers in Canada formed a dam blocking the rivers flowing from the south so they backed up and formed a gigantic lake.
Lake Agassiz was 700 miles long, 200 miles wide, and 300 feet deep.
Lake Agassiz existed for about 4,000 years.
The Red River Valley is the lake bed of the ancient Lake Agassiz.
Mastodons and woolly mammoths lived in North Dakota about 11,000 years ago.
The area of the state not touched by the Wisconsinan glacier is called the Badlands.
Red rock formed from lignite coal burning underground is called “clinker” or “scoria."
