What Is Soil?
Soil is the organic material that makes up most of our planet’s surface. It includes all the plants, trees, grasses, shrubs and other vegetation that grows there. Most soils are made from different types of materials such as sand or clay. Sand is usually loose and sandy while clay is hard and compacted like concrete. There are many kinds of soil but they all have one thing in common – They’re all made out of plant matter!
The term “soil” comes from the Latin word sanguis meaning blood. It was originally used to refer to human blood because it contains the same substances found in human blood. However, over time it came to mean any kind of earthy material that could not be cultivated. Today, soil refers only to the earth itself and does not include living organisms such as plants or animals.
How Does Soil Drain?
There are several ways that soil can drain. These methods depend on the type of soil and its physical characteristics. Some soils are very slow to drain while others can drain within minutes. All soils have pores (holes) where water may enter them, however some pore sizes are larger than others and these determine which soil will drain faster or slower.
Porous soils with small holes tend to hold onto moisture longer than porous ones with large holes. The size of the holes in a given soil determines how fast it drains. The fastest draining soils have the smallest holes while the slowest draining soils have the largest.
Soils with large pores are said to be permeable or loosely compacted while those with small pores are said to be non-permeable or tightly compacted. Loosely compacted soils are able to absorb more water than tightly compacted ones. Water is absorbed at a faster rate and pore spaces tend to be larger than those in other soil types. Loosely compacted soil drains faster than most other types of soil.
Soil that can absorb large amounts of water without drainage are said to be infiltraite. These are mainly composed of sand and may be slightly permeable or impermeable. They do not retain much water and can dry out quickly when exposed to the sun.
Soil that retains a lot of water without draining is called “wet soil”. Soil that retains only a moderate amount of water without drainage is called “moist soil”. Wet and moist soil types are composed mainly of silt and clay and retain most of the water that enters them. Wet and moist soils usually drain very slowly, if at all.
Water can enter through the surface or from below ground. Water from below ground rises upward by way of capillary action. This type of water movement is slow and can take considerable time to reach the surface. Wet soils usually drain very slowly or not at all because water enters them slowly and then cannot escape.
Acid And Alkaline Soil
Some soil types have a higher acidity than others, such as peat, which tends to be acidic, while chalk tends to be basic or alkaline. The term “acidity” refers to soil that has a pH value of 7 or below. Alkalinity is defined as soil with a pH value of 8 or above.
Water has a pH value ranging from 0 to 14, with 7 being neutral. Water with a pH value of less than 7 is acidic and water with a pH value of more than 7 is alkaline. Soils with a pH level 7 are neither acidic nor alkaline.
Soil acidity and alkalinity are important to plant growth. Some plants such as rhododendrons thrive in acidic soil while others such as blueberries do better in alkaline soil. Most plants do best in a soil that is slightly alkaline with a pH level of 7.
Recent studies have proved that the type of soil a plant grows in influences the taste of certain fruits and vegetables. Tomatoes grown in soil with a high alkaline content tend to have a sharper taste than those grown in acidic soil.
Soil erosion is the wearing away of soil by wind or water. Water can transport away small amounts of soil, but most erosion is caused by wind blowing soil away.
Water that flows over the surface of the soil can also erode it. Rain is the cause of most soil erosion because it washes small bits of soil away.
The loss of soil by erosion is a serious problem in many parts of the world. It not only makes the soil unusable for farming or gardening, it also makes the land unfit to live on.
Water erosion is the most common type of soil erosion. Water carries soil away in tiny particles. As long as there is an abundant supply of water, this type of erosion can go on forever.
Gentle slopes are especially susceptible to water erosion. Rainfall or snowmelt washes soil downhill in a process called gullying. Trees along the hillside help to hold the soil in place by their roots. If people cut down the trees for firewood or building material, the soil may no longer be held in place and will continue to wash or gully downhill.
Water erosion is also a problem on flat land. Rivers cut deeper channels into the ground as they flow across the plain, especially during the rainy season. This process is called channel erosion. Usually, people do not notice this type of erosion until they notice that the river is changing its course.
Another cause of water erosion is overflowing rivers during the rainy season. Floods destroy crops and wash away topsoil. This causes people to clear more land for agriculture, which in turn leads to even worse flooding. This process is called a cycle of erosion.
Flooding not only causes soil erosion but also damage to property and loss of life.
Dust storms are a form of soil erosion that occurs mainly in arid or semiarid regions. Strong winds pick up the topsoil and carry it over large areas. The dust clouds eventually settle over adjacent land or ocean, leaving the land without topsoil.
Giant dust storms in North America occur mainly in the states of Texas, Oklahoma, Kansas, and New Mexico. In these areas, the lack of rainfall and sudden severe thunderstorms called haboobs scoop huge amounts of soil from the ground.
An example of a haboob occurred in Arizona on May 9, 2011. It started as a small thunderstorm that quickly grew stronger and bigger. By the time the storm had passed, it had turned day into night. The dust cloud was so large that it covered an area from California to New Mexico.
The Dust Bowl of the 1930s was the worst time for dust storms in North America. For more than a decade, these storms covered vast areas of land. More than 500,000 square miles were affected. Crops and pastures were destroyed, and people were forced to leave their homes because there was nothing left to eat or farm.
The main cause for the Dust Bowl was overgrazing by cattle. The cattle destroyed the natural grasses and plants that held the soil in place. When severe drought struck the region, the soil turned into dust and blew away on the wind.
The only way to control dust storms is to plant and protect natural grasses and plants.
People can also divert rainwater into streams and rivers to prevent flooding and channel erosion. They can also build barriers to hold back floodwaters.
The building of dams on rivers can cause a danger called silting. As the name suggests, silt and mud collect at the bottom of the dam and fill up the reservoir, making it unusable by humans or animals.
“The stone that the builders rejected has become the cornerstone.”
In this section, you will learn about the history of stone tools and how archeologists classify and locate ancient human sites.
Striking Stones Together
In the earliest times, people made tools from stone by chipping or flaking pieces of rock. This is called hard-hammer flaking. The best tool rocks are called stones.
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