The Ice Age
The Earth is about 4.6 billion years old and there have actually been about 11 different Ice Ages. An Ice Age is a cold period in which glaciers, slowly moving sheets or masses of ice, covered much of the Earth's surface. The last ice age on Earth was called 'The Great Ice Age' occurring about 11,000 years ago. Over 1/3 of the Earth's surface was covered in ice, and the air had less carbon dioxide in it.
Two explanations are usually given as to why the ice ages occurred. One, the temperatures were so cold that it never rained, only snowed. Two, the tilt of the Earth changed and it was away from the Sun.
The land looks much different during an ice age. It is frozen and bare land which is called a tundra. Very few plants exist on a tundra since the ground is too frozen to sustain life. There are evergreen trees that grow but there is no grass or flowers, only shrubs, bushes, and moss grass. In some parts of the world there are still tundra in parts of North America, Europe, and Asia.
Following the end of the last Ice Age there were glaciers left behind and the sheets of ice covered rivers and valleys. The melting and the refreezing of the ice continued to occur for millions of years. Then, about 10,000 years ago the Earth began to get warmer and the remaining glaciers melted leaving lakes and valleys with a mixture of rocks and soil. However, in the higher elevations there was still ice and glaciers, including some today that were left over from the last Ice Age.
A scientist named Louis Aggasiz studied the clues of the ice age in the 1800s. He explained to other scientists that boulders they saw were left by glaciers and carrying them many miles from one area to another. The other scientists did not believe him. However, Aggasiz proved his theory because boulders the glaciers left behind were made of granite. There were no other granite boulders in the area so they had to have been brought there by the glaciers. Other things also proved his theory. There was polished bedrock, large sand and gravel piles, big valleys, and rough mountain tops, which were all formed by the movement of the glaciers during the ice age.
Even though ice ages took place, there were still animals living on the Earth including the wooly mammoth, wooly rhinos, cave bears, horses, wolves, bison and reindeer. A few of them are now extinct such as the woolly mammoth, cave bear, and woolly rhino. Scientists know they existed though because there were people who painted pictures of the animals on the sides of the caves where they lived.
There have been skeletons of the animals found as well. In addition, cuts of bones have been found in these skeletons which were made by the knives of the hunters. Some of the knives the hunters used were found next to the skeletons too.
People also lived during the Ice Age 35,000 years ago. The role of the men included hunting for food, and the women and children prepared the food, made clothing from the hides of animals, and built the shelters where everyone lived.
When the hunters killed an animal, every part of the animal was useful. Its meat and organs were used for food. The skins were used for their clothing, blankets, and shelter. Even an animal's stomach was used for carrying water. Finally, the bones were used for needles, weapons, and different tools.
In summary, and ice age is when much of the Earth's surface is covered by glaciers, but there may still be living organisms that survive in the cold climates such as those on a tundra.