ENVIRONMENTAL SCIENCE
Environmental Science: The environment is man’s first right. Without a safe environment, man cannot exist to claim other rights, be they political, social, or economic. The term “environment” comes from the French word *Environia*, meaning to surround. The environment can be broadly defined as one’s surroundings. Specifically, it is the physical and biological habitat that surrounds us. According to P. Gisbert, “Environment is anything immediately surrounding an object and exerting a direct influence on it.”
Classifications of Environment
1. **Physical Environment**: External physical factors like air, water, and land. Also called the abiotic environment.
2. **Living Environment**: All living organisms around us, such as plants, animals, and microorganisms. Also called the biotic environment.
Components of Environment
The Earth’s environment can be further subdivided into the following segments:
–Atmosphere
-Hydrosphere
– Biosphere
– Lithosphere
Atmosphere
The atmosphere is a gaseous layer surrounding the Earth. In simpler terms, our Earth is enveloped by a thin layer of gases, known as the atmosphere.
Gases in the atmosphere are categorized into two types: constant gases and variable gases. Constant gases have concentrations that do not change over time and remain relatively stable. Nitrogen and oxygen are the major constant gases, constituting 78.09% and 20.94% of the atmosphere by volume, respectively. Nitrous oxide, ozone, water vapor, and carbon dioxide make up 0.94% of the atmosphere by volume.
Variable gases, on the other hand, have concentrations that change from time to time and place to place. Carbon dioxide (0.03%), water vapor, and ozone are considered variable gases.
The Earth’s Atmosphere
The Earth’s atmosphere blankets the planet, keeping temperatures stable and shielding living organisms from harmful solar radiation. This protective layer of gases extends hundreds of kilometers, from the Earth’s surface into outer space. Generally, the density of atmospheric gases decreases as altitude increases, and atmospheric pressure follows a similar pattern, decreasing with distance from the Earth’s surface.
However, air temperature follows a less consistent pattern, sometimes decreasing and sometimes increasing with altitude, depending on the atmospheric layer. Scientists have used this zigzag temperature pattern to define five distinct layers of the atmosphere, each with unique chemical compositions and temperature variations.
The layers, starting from the lowest, are: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each layer surrounds the Earth, hence the suffix “sphere.”
Troposphere:
– Starts at Earth’s surface and extends up to about 12 km.
– We live in this layer, and it’s where weather happens (clouds, precipitation, etc.).
– Most commercial aircraft fly within this layer.
– Both temperature and air pressure decrease with altitude, reaching as low as -53°C.
Stratosphere:
– Starts about 12 km above Earth’s surface and extends up to about 50 km.
– Contains the ozone layer, which protects us from harmful ultraviolet radiation.
– Temperature increases with altitude in this layer, reaching up to -03°C.
Mesosphere:
– This is the middle layer of the atmosphere, starting at about 50 km and extending up to 80 km high.
– Most meteors burn up in this layer, making it the coldest layer of the atmosphere.
– The temperature decreases as altitude increases, dropping as low as -93°C.
Thermosphere:
– Named for its high temperatures, this is the hottest layer of the atmosphere.
– It is where auroras are formed due to the charged particles in the ionosphere.
– The temperature increases with height, rising up to 2000°C or higher.
Exosphere:
– The outermost layer of the atmosphere.
– Temperatures are very high but can vary depending on location.
– This is where satellites travel and this layer blends into outer space.
Temperature Variations:
– Temperature variations in the five layers are due to the absorption of solar energy as it moves downward through the atmosphere.
– The Earth’s surface is the primary absorber of solar energy, reradiating it as heat, which warms the overlying troposphere.
– The temperature in the troposphere rapidly decreases with altitude until the tropopause, the boundary between the troposphere and the stratosphere.
– In the stratosphere, temperature increases with altitude due to ozone (O₃) absorbing ultraviolet radiation from the sun.
– At the stratopause, temperature stops increasing with altitude.
– The mesosphere does not absorb solar radiation, so temperature decreases with altitude.
– At the mesopause, the temperature begins to increase with altitude, continuing in the thermosphere.
Atmosphere Classification:
– The atmosphere can also be classified based on electrical properties into the neutralsphere and ionosphere.
– The ionosphere, lying 60-1000 km above the Earth, is ionized by solar and cosmic radiation, resulting in positively charged ions and free electrons.
– The Sun’s upper atmosphere, the corona, produces plasma, UV, and X-rays that ionize the Earth’s ionosphere, which is important for reflecting and modifying radio waves used for communication and navigation.
Importance of the Atmosphere:
– The atmosphere is vital for sustaining life on Earth, containing life-supporting oxygen in large quantities, and maintaining a constant concentration through oxygen and carbon dioxide cycles.
– It absorbs most infrared radiation and prevents the Earth from getting too cold at night.
– The ozone layer in the stratosphere blocks about 95% of harmful ultraviolet radiation from reaching the Earth’s surface.
– The atmosphere’s heat energy, in the form of infrared radiation, is absorbed by carbon dioxide, water, and other gases, creating a “greenhouse effect” that keeps the Earth warm even without sunlight, resulting in diverse weather patterns.
Wind Currents
These wind currents operate on both global and local scales. They can lead to disastrous weather events such as cyclones, dust storms, and tornadoes. Additionally, they influence ocean currents, which in turn affect wind patterns. Understanding the atmosphere, including these dynamics, is complex yet essential for a comprehensive grasp of weather and climate systems, contributing to our understanding of the dynamic nature of the atmosphere.
Hydrosphere
The hydrosphere encompasses all the water on a planet, including water on the surface, underground, and in the atmosphere. This water exists in various forms: liquid in oceans, lakes, and rivers; vapor in the atmosphere; and ice in glaciers, ice caps, and icebergs. The frozen component of the hydrosphere is known as the cryosphere.
Global Water Distribution
An inventory of Earth’s water resources indicates that approximately 97% of the global water supply is found in the oceans, which are saline. A small fraction of saline water is also present in saline lakes, like the Caspian Sea. The remaining 3% of the Earth’s water inventory is freshwater.
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Freshwater Storage
Freshwater is primarily stored in permanent ice, including continental and mountain glaciers, accounting for nearly 69% of the total freshwater supply. About 30% of freshwater exists as groundwater beneath the Earth’s surface. Only about 1% of freshwater is found in surface water sources such as lakes, streams, and marshes. Minute amounts of freshwater are also present in the soil, the atmosphere, and within biological organisms.