Weathering and Soil

Weathering and Soil Based on Discover God’s Creation, chapter 5 By Rebecca Fraker

Processes That Change Earth’s Crust Weathering breaks up or changes rocks. • Physical weathering simply breaks rock into smaller pieces. • Chemical weathering dissolves rock and changes it into new substances. Erosion: moves the pieces of weathered rock to new locations.

Five main forces of physical weathering: • Heating and cooling, • Internal pressure • Water • Wind • Plants and animals

Heating and Cooling • Heating and cooling, from changes in the weather, cause rocks to expand and contract. • As they do, pieces break off the rock’s surface.

Internal Pressure • In some rock formations, internal pressure makes their outer layers peel away. • This often happens to granite, creating large dome formations. It can also happen in mines and quarries. • As workers remove rock, pressure in the underlying rock is released, causing pieces of rock to explode outward. • Miners refer to this as “flying rock”.

Water • Water is also a force of physical weathering. • When water runs into the cracks of rocks, then freezes, it expands and breaks the rock apart.

Lost Sea WATER • In streams and rivers, water-borne sand and gravel scrape the rock that forms the bottom and sides of streams and rivers, slowly wearing the rock away. • The largest underground lake is the Lost Sea. It lies 300 feet underground in Tennessee and covers over 4 acres.

Wind • Wind loosens and lifts away small particles of rock. • Sand and small pebbles carried by strong winds create a “sand-blasting” action that wears away rock surfaces. • This often results in unusual “wind-carvings” and landscapes.

Plants and Animals • Often plant roots grow into the cracks in a rock. As the roots extend into a crack, the rock is forced apart. • Animals such as ants, worms, moles, meerkats, groundhogs, and so on break up the crust by burrowing in the soil, allowing water to get to the rocks below.

People • People also break up Earth’s crust. Blasting done in mines and quarries breaks rock apart. • Construction of dams and roads also helps to break up Earth’s crust.

Internal pressure

One hundred years ago, the state of Iowa was covered with over 16 inches of topsoil. It was held in place by deep-rooted grasses. • As farmers moved west, they plowed up these grasses and planted other crops. Often the soil lay bare. When drought hit, the wind was able to blow much soil away. The area became known as the dust bowl. • Today, less than half of that topsoil (8 inches) remains

Chemical Weathering • Chemical weathering is different from physical weathering because it actually changes rock into new substances.

Water and chemical weathering • Water acts on rock by dissolving the rock’s minerals or by combining with them. • Sometimes the dissolved minerals join with other minerals to form new rock. • When water combines with minerals in the rock, the rock may swell, become soft, and fall apart.

Oxygen and chemical weathering • Oxygen in water and air combines with the minerals in rock to form oxides. As oxides form, the rock’s surface begins to loosen, allowing oxygen to penetrate deeper into the rock. • New oxides form as oxygen reacts with the rock’s deeper layers. This process can continue until the rock is completely changed.

Acids • Acids also chemically change rocks. • Some acids form when water combines with minerals in the soil. • One such acid, called carbonic acid, breaks down limestone. • In some places, large amounts of limestone have dissolved underground, leaving caverns or caves.

Plants • You can easily break a mushroom with your fingers, but the same mushroom can push with enough force to break through 15 inches of pavement! • Even some plants such as lichen produce acids that dissolve rock.

Burning fossil fuels: • Some fossil fuels such as coal and oil produce gases that combine with rain and snow to form acid rain which can dissolve stonework and metal in buildings. • This same acid rain can kill fish and plants.

Effects of Acid Rain

5-3 SOIL

Weathering breaks rock into smaller and smaller pieces. Erosion moves these particles and deposits them in new locations. Soil is formed as this broken rock mixes with decayed material, water and air.

Soil is made from the bottom up as well as from the top down. Dead plant and animal material form humus at the top. At the bottom, parent rock weathers to form subsoil. Topsoil is humus mixed with subsoil. It is the most important part of the soil. It provides food for plants, insects, and animals, as well as homes for many animals.

Textures of Soil • Scientists identify three kinds of soil texture: • Sandy • Clay • Loamy

Sandy soil • The texture or size of soil particles is important. It determines how well the soil holds water and minerals needed by plants. The largest particles in soil are sand; the smallest are clay. • When a soil is made up of mostly large particles, it is sandy.

Clay soil • When solid is made up of mostly small particles, a clay-texture soil is created. Clay soil will often pack very hard and make it difficult for plants to grow.

Loamy-textured soil • When the particles of sand and clay are mixed evenly it results in loamy soil.

Factors that determine the type of soil: • Type of rock lying beneath the soil • Topography of the land • Climate • Amount of humus

Variety of Soils • The six basic types of soil are classified based on location, texture, and minerals. • Forest • Prairie • Desert • Tropical • Mountain • Tundra forest prairie desert tropical mountain tundra

Weathering and Soil