Weathering – Factors and Formation of Soil

Introduction:

You’ve studied that the Earth is the place where we live. 70% of the Earth is covered with water. Earth is a unique planet. It supports life for many years. Earth is round in shape, and it is not a solid piece of rock. It is made up of different layers.

Earth is also called a water planet or blue planet due to the presence of water on it.

There are many features on the Earth’s surface such as mountains, hills, plains, waterfalls, etc. These features are called landforms.

There are many factors such as wind, water, chemicals, and depositions that shape the land.

Various shapes of rocks on Earth are formed by weathering and erosion.

What is Weathering?

You’re hiking through the desert in Utah’s Arches National Park. You come around a corner and notice a large window in the middle of a rock. It used to be a massive, solid rock. What caused the rock’s transformation?

Rocks are always changing. Rocks can break into smaller pieces due to freezing and thawing, plants, wind, and pressure. Weathering is the process by which rocks break down.

Wind and rain break down rocks, which causes physical weathering. Rocks change size and shape due to physical weathering. The chemicals that make them up do not change. Let us see the things, that cause physical weathering.

Factors that Cause Physical Weathering

1. Freezing and Thawing:

Rainwater or melted snow enters small cracks in rocks. Water expands or takes up more space when it freezes. This causes cracks to enlarge. The water may later thaw or melt. The repeated freezing and thawing of rocks breaks them apart over time.

2. Plants:

Have you ever tripped on a cracked sidewalk caused by tree roots? The roots of plants can push their way through small cracks in rock. The roots cause the cracks to widen and the rocks to break apart as they grow in size.

3. Exfoliation:

When heavy layers of rock wear away, some buried rocks, such as granite, change. The outer layers of the once-buried granite expand faster than the layers beneath it. This causes the rock’s outer layers to peel away like the layers of an onion. Exfoliation is a type of physical weathering.

4. Abrasions (scratches):

Winds can also cause rocks to shift. Winds that carry sand can erode the softer parts of rocks. Sand’s sharp edges wear away rock. Wind abrasion is the wearing away of rock by blowing sand.

Other Causes of Weathering

Have you ever seen a weathered stone statue? What must have caused the weathering?

Chemical weathering

Chemical weathering, most likely, caused the changes. When the minerals in a rock undergo chemical changes, they break down.

Chemical weathering occurs when these changes occur. Chemical weathering can occur when oxygen, acids, and carbon dioxide react with minerals in the rock.

Oxygen

Have you ever noticed an iron chain rusting over time?

This occurs when the oxygen in the air dissolves in water. Rust is formed when it reacts with iron. Iron-containing rocks can also rust and degrade.

Acids

The majority of the water in rivers and soil is acidic. Plants that die release acids into the soil. These acids are dissolved in the soil by water. When dissolved acid comes into contact with rock, it reacts with the minerals in the rock. Chemical changes occur in the rock. The rock eventually changes shape and breaks down.

Carbon dioxide

Carbon dioxide, a gas present in the atmosphere, reacts with rainwater. By this reaction, carbonic acid is formed. This acid can react with minerals present in certain rocks. The formation of the limestone cave shown below was caused by carbonic acid.

Carbonic acid also weathers rock present in the soil. Carbon dioxide is released into the soil by decaying plant and animal matter. Rainwater seep into the soil and reacts with carbon dioxide.

Formation of Soil

When you look at soil through a hand lens, you will notice that it contains a variety of elements. Soil is mainly made up of weathered rock, minerals, and humus. Humus is decomposed plant or animal matter. Water, air, and bacteria are also present in the soil. Weathering can take thousands of years to break down rocks and form soil.

Horizons are layers of soil that form over time. Each horizon has its specific set of characteristics. Soil horizons differ from one location to the next. That’s because the rocks and humus that makeup soil vary by location.

In some places, the horizons may resemble those depicted below.