Changing Times

North America hasn't always looked as it does today. In the past 600 million years parts of it have been submerged under shallow seas, covered by thick tropical forests, and buried under thick sheets of ice.

Today we will look at one state, Wyoming.  We will see how it has changed since prehistoric times.

Wyoming today:
     -is mostly flat and covered by grasses and scattered trees
     -gets very little rainfall
     -is bordered by rugged mountains
     -has warm summers and cold winters
     -has bighorn sheep, moose, mule deer, elk, pronghorn antelope, praire dogs, bison, bald eagles,
      golden eagles, thrushes, trout, and many other wild animals.

Wyomoing has not always looked this way.

Pass out page 53 Naturescope: Geology: The Active Earth

The pictures on the left show how Wyoming looked at different times long, long, ago.

Picture 1   About 550 million years ago, a warm shallow sea streteched across much of North America, including Wyoming.  Jellyfish, sea worms, and many other sea creatures were common.  But fish, turtles, and many other animals that live in the seas today had not yet appeared.

Picture 2   Millions of years later, the seas had dried up and tropical forests covered much of the land.  The temperatures were warm throughout the year. Many new forms of life had appeared, including fish, birds, reptiles, mammals, and flowering plants.

Picture 3   About 100,000 years ago the temperatures in North America were much colder.  Most of the tropical forests had died out and had been replaced by plants that could live in cold temperatures.  In the coldest areas of the north, snow began to pile up on the ground, forming thick layers.  Over time this snow turned into huge sheets of ice that covered much of North America.  Some animals died out during these frigid times.  But others adapted to the colder climate.

Mammoth  This animal had thick underfur and long outer hairs that kept it warm.  It was as big as an elephant.  It used its long tusks to dig grass and other plant foods from beneath the snow.

Trilobites   Most of these animals were smaller than your hand and lived in the ancient oceans.  They had a hard outer covering just as crabs, insects, and many other animals have today.  They had many legs, which they used like paddles to move through the water and to crawl along the seafloor.  Most of them ate bits of dead plant and animal material.

Triceratops   This dinosaur was well protected from enemies.  Its body was covered with tough, thick skin and it had three sharp horns on its head to help defend itself.  This animal was a plant eater and often traveled in herds like many other plant-eating doinosaurs.