Solar Radiation, Climate Change, and Soil Formation
The Sun: Earth’s Closest Star
The sun, the closest star to Earth, is a huge sphere of gases, primarily hydrogen and helium. Its innermost zone is the outer core and the photosphere. Hydrogen atoms join to form helium atoms in a process called fusion, which releases energy. The energy from the sun is emitted in all directions into space as solar radiation. The closer a planet is to the sun, the more energy per square meter it receives.
The Atmosphere
The atmosphere is the layer of gases enveloping the Earth. It consists of several zones:
- Troposphere: The lowest layer of the atmosphere, where clouds form and all atmospheric phenomena occur.
- Stratosphere: Contains the ozone layer, which absorbs ultraviolet radiation.
- Ionosphere: A very tenuous layer.
- Exosphere: The outermost layer, transitioning into outer space.
Sunscreen Effect of the Atmosphere
The sun emits visible light in addition to a set of radiation ranging from ultraviolet to X-rays and gamma rays, which are lethal to living things. The atmosphere acts as a natural sunscreen, protecting life on Earth.
Albedo
Albedo is the portion of solar energy that is reflected back into space and therefore does not contribute to heating.
Unequal Distribution of Solar Radiation
There is an unequal distribution of solar radiation on Earth. This is caused by the Earth’s spherical shape and the tilt of its axis of rotation.
Consequences of Earth’s Shape
If the Earth were flat, solar radiation would reach all areas equally. However, its spherical shape has two consequences:
- Solar radiation arrives at different angles in different areas.
- The length of the path of solar radiation through the atmosphere varies; it is shorter if it arrives at a right angle than if it arrives at an oblique angle.
Effects of the Inclination of Earth’s Axis
If the Earth’s axis were perpendicular to the ecliptic, all points on the globe would have 12 hours of daylight and 12 hours of night. However, the axis is tilted. This tilt has the following consequences:
- It changes the length of day and night.
- It changes the angle at which the sun’s rays reach the Earth.
The seasons are the result of the tilt of Earth’s rotation axis and its translation along the ecliptic.
Greenhouse Effect
Solar radiation passes through the atmosphere, warming the surface of continents and oceans. Once heated, the surface releases heat towards the exterior. Some components of the atmosphere, called greenhouse gases, trap heat and reduce heat loss.
Climate Change
The increase in carbon dioxide is causing the greenhouse effect to intensify. This has led to changes in the Earth’s temperature and other effects, including:
- Rising temperatures
- Shrinking glaciers
- Melting ice, leading to higher sea levels
- More frequent floods and heat waves
All of the above changes affect ecosystems.
The Wind
Wind is moving air. There are two types:
- Vertical: Hot air, being less dense, rises. As it rises, it cools and descends.
- Horizontal: Air moves across the surface to fill the space left by the rising hot air.
Vertical and horizontal motions are not independent; together, they form convection currents.
Rocks and Soil Formation
If rocks remained unaltered, vegetation could not take root. The internal appearance of rocks differs from their external appearance.
Weathering
Weathering refers to the alterations that rocks undergo. It can be physical or chemical.
Physical Weathering
Physical weathering is the division of rocks into fragments. Causes include:
- Temperature changes: Rocks expand when heated and contract when cooled. If there are significant temperature differences, rocks can crack.
- Gelifraction: Water can seep into cracks in rocks and freeze. As water expands upon freezing, it can cause the rocks to break. This is important in high mountain areas.
Chemical Weathering
Oxygen and carbon dioxide from the air, along with water, cause changes in the chemical composition of rocks. Examples include:
- Oxidation: When iron in rocks rusts, the rocks lose consistency and break more easily.
- Dissolution: Some rocks and minerals, such as gypsum, dissolve easily in water. This is important in humid climates.
Living Things and Rock Alteration
Some organisms dig into the soil and contribute to rock alteration. Plants also introduce their roots into the soil, further breaking down rocks.
Soil Formation (Pedogenesis)
The process of soil formation is called pedogenesis. It is produced by the weathering of rocks caused by water, air, and living things.
- Native soils: Soils that originate in situ, on the bedrock.
- Allochthonous soils: Soils that may be formed away from the bedrock.
Factors Influencing Soil Formation Rate
- Rock type: The more resistant the rock, the longer it takes for soil to form.
- Climate: Soil formation is faster in wet and warm climates.
- Topography: Soil formation is difficult in sloped areas.
- Vegetation: Abundant vegetation promotes soil development.
Soil Composition
Soil is composed of:
- Fragments of rocks and minerals: gravel (coarse materials), sand (medium size), and clay (very fine size).
- Organic matter: microorganisms (bacteria, fungi), remains of organisms, and humus.
- Air
- Water
Soil Characteristics
Texture:
- Sandy soil: Coarse particle size, porous.
- Clay soil: Very fine particle size, slightly porous.
Profile: Each layer is called a horizon.
- Horizon 0: Thin layer with organic matter.
- Horizon A: Dark layer with humus and roots.
- Horizon B: Lighter layer with few roots and little humus.
- Horizon C: Parent rock.
Soil Biocenosis
- Producers: Autotrophs.
- Consumers: Heterotrophic organisms that feed on living organic matter.
- Decomposers: Heterotrophic organisms that feed on dead organic matter and transform it into mineral matter.
Soil Biotope
The soil biotope is the place occupied by the soil biocenosis.
Soil Degradation and Loss
Causes of soil degradation include:
- Deforestation: Using wood and replacing forests with farmland.
- Overexploitation of crops: Overuse of fertilizers.
- Overgrazing: Excessive consumption of grass by livestock.
Soil Protection
To protect soil, avoid overuse, create terraces on slopes for planting trees, and rotate crops.