Figure 1. This bluff was formed when soil was eroded by water in Cheyenne County in northwest Kansas.
The Earth is billions of years old. In Kansas, hills were formed that were later buried or worn away by wind and water. Seas covered parts of the state, then disappeared. Giant sheets of ice called glaciers moved into northeast Kansas, then melted. Rivers changed their courses. The climate changed--sometimes hot, sometimes cold, sometimes wet, sometimes dry.
These changes are what made Kansas look the way it does today. Looking around, it's hard to believe that changes are still taking place. We rarely notice them because they happen so slowly. But every time it rains or the wind blows, dirt and rock are worn away from hills, valleys, and plains. This process of wear and tear is called erosion. Over just a few years or even a few hundred, it's hard to tell that things are changing, but over millions of years whole mountains may erode away or be buried.
Sometimes changes happen more quickly. Floods can cause rivers to change course almost overnight. The Missouri River, which is the state line in northeast Kansas, has changed course several times. Small areas of land that were once on the Kansas side of the river are now on the Missouri side. Missouri has also lost some land to Kansas.
Figure 2. Castle Rock is a natural chalk sculpture in Gove County in western Kansas. In this photograph, taken in the late 1800's, Castle Rock had two spires taller than the rest. One of the spires eventually toppled (photo courtesy of the Kansas Historical Society).
Figure 3. Today Castle Rock only has one tall spire. The other one collapsed due to erosion by wind and water.
Wind and water are just two of the many forces that are changing the world around us. The force of gravity, which holds us to the Earth, causes eroded rocks to roll off mountains and hillsides into valleys and river beds.
Unstable conditions inside the Earth also cause changes. Volcanic eruptions, such as Mount St. Helens in Washington in 1980, can cause immediate changes. When Mount St. Helens erupted, the top of the mountain blew off and volcanic ash was carried thousands of miles by the wind. Millions of years ago, active volcanoes in New Mexico, Wyoming, and California erupted and large quantities of ash were carried into Kansas. Today, volcanic-ash deposits can be found in western Kansas.
Earthquakes, which accompany volcanoes or the shifting of underground rocks, can change the environment. Most earthquakes in Kansas are small and can only be detected by sensitive equipment. However, some have been intense enough to cause damage. In 1867 an earthquake in northeast Kansas shook buildings, knocked over chimneys, and cracked walls. Most changes caused by earthquakes are underground and not as obvious as changes caused by volcanoes. But, over time, earthquakes help to change the way the surface of the Earth looks.
People also have greatly changed the environment by plowing fields, quarrying rocks and minerals, building cities and roads, and damming rivers. Try to imagine what Kansas would look like without farms, buildings, roads, and cities--without people.
How do we learn about geologic changes over time? Without people to write books or take pictures, the only records we have of the Earth's early history are hidden in the land around us. Since the Earth isn't talking, scientists must search for answers. The study of what the Earth is made of and how it changes over time is called geology. Scientists who study the Earth are called geologists.