Comprehensive theory, key formulas, diagrams, and memory aids for Natural Resources.
Our planet, Earth, is the only one on which life, as we know it, exists. Life on Earth is dependent on many factors. Most life forms we know need an ambient temperature, water, and food. The resources available on Earth and the energy from the Sun are necessary to meet the basic requirements of all life forms on the planet.
What are these resources on Earth? They are the land, the water, and the air. * Lithosphere: The solid outer crust of the Earth. * Hydrosphere: The water that covers 75% of the Earth's surface and is also found underground. * Atmosphere: The air that covers the whole Earth like a blanket.
The life-supporting zone of the Earth where the atmosphere, the hydrosphere, and the lithosphere interact and make life possible is known as the Biosphere. Let's look closely at these resources and how they are cycled through nature.
Air is a mixture of many gases like nitrogen, oxygen, carbon dioxide, and water vapour. On planets like Venus and Mars, where no life is known to exist, the major component of the atmosphere is carbon dioxide (up to 95-97%). On Earth, carbon dioxide constitutes only a fraction of a percent because it is continuously used up by plants for photosynthesis, and dissolved in oceans to form carbonate rocks.
The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year. Air is a bad conductor of heat. It prevents the sudden increase in temperature during daylight hours, and during the night, it slows down the escape of heat into outer space. Contrast this with the moon (which has no atmosphere), where the temperature ranges from $-190^\circ\text{C}$ to $110^\circ\text{C}$.
We have all felt the relief brought by cool evening breezes after a hot day, and the devastating force of cyclones. These phenomena are the result of changes that take place in our atmosphere due to the heating of air and the formation of water vapour. * When air is heated by radiation from the heated land or water, it becomes lighter and rises. * Since land gets heated faster than water, the air over land rises faster, creating a region of low pressure. * Air from a high-pressure area (over the sea) moves into this low-pressure area (over the land). This movement of air from one region to another creates winds.
The increase in the content of harmful substances in the air is called air pollution. Fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur. When burnt, they produce oxides of nitrogen and sulphur. These gases are dangerous to inhale and dissolve in rain to give rise to acid rain. The combustion of fossil fuels also increases the amount of suspended particles in the air (unburnt carbon particles or hydrocarbons), which lowers visibility (causing smog in cold weather) and increases the incidence of allergies, cancer, and heart diseases.
Water occupies a very large area of the Earth's surface. Most of the water on Earth's surface is found in seas and oceans and is saline (salty). Fresh water is found frozen in ice-caps and glaciers, and underground.
Water pollution happens when harmful substances (like chemicals from factories, sewage, fertilizers, and pesticides from farms) are discharged into water bodies. This can cause: 1. The addition of undesirable substances to water bodies (causing diseases like cholera). 2. The removal of desirable substances (like dissolved oxygen, which aquatic animals need). 3. A change in temperature (thermal pollution), which can disrupt the breeding of aquatic organisms.
Soil is an important resource that decides the diversity of life in an area. Over millions of years, the rocks at or near the surface of the Earth are broken down by various physical, chemical, and some biological processes. The fine particles formed are soil.
Factors making soil: * Sun: Heats rocks during the day (they expand) and they cool at night (they contract). This uneven expansion and contraction causes cracks. * Water: Gets into cracks, freezes, and widens them. Fast-flowing water also carries and rubs rocks against each other, breaking them down. * Wind: Rubs rocks and carries sand from one place to another. * Living Organisms: Lichens growing on rocks release substances that powder the rock surface. Plant roots go into cracks and force them wider.
Soil contains bits of decayed living organisms called humus, which makes soil porous and allows water and air to penetrate deep underground. Soil Erosion: The carrying away of topsoil by wind and water. Deforestation significantly increases soil erosion, leaving barren land.
A constant interaction between the biotic (living) and abiotic (non-living) components of the biosphere makes it a dynamic but stable system. These interactions consist of the transfer of matter and energy between different components.
Water evaporates from water bodies, falls as rain, and eventually flows back into the sea via rivers. This whole process, including the formation of clouds and rain, is the water cycle. It is not just water moving; flowing water wears away rocks and carries soluble minerals to the sea, making them available for marine organisms.
Nitrogen gas makes up 78% of our atmosphere. It is essential for many molecules essential to life like proteins, nucleic acids (DNA and RNA), and some vitamins. * Nitrogen Fixation: Most life forms cannot use nitrogen gas directly. It must be converted into nitrates and nitrites. This is done by nitrogen-fixing bacteria (like Rhizobium found in the root nodules of legumes) or physically by lightning during storms. * Plants take up these nitrates to make proteins. Animals consume plants. * When animals and plants die, other bacteria in the soil convert the complex nitrogen compounds back into simple nitrates. A different type of bacteria converts nitrates back into nitrogen gas, releasing it into the atmosphere.
Carbon is found in various forms: as elemental carbon (diamonds and graphite) and as carbon dioxide in the atmosphere. * Carbon is incorporated into life forms through photosynthesis performed by plants in the presence of sunlight. * This carbon is passed on to animals when they eat plants. * Carbon is returned to the atmosphere as $CO_2$ through respiration (by plants and animals), the decomposition of dead matter, and the combustion (burning) of fossil fuels.
The Greenhouse Effect: Some gases (like Carbon Dioxide, Methane) prevent the escape of heat from the Earth. An increase in the percentage of such gases in the atmosphere causes the average temperature to increase worldwide. This is called the greenhouse effect and leads to global warming.
Oxygen is very abundant (21% of the atmosphere). It is essential for respiration and combustion. * Oxygen is used up in three processes: combustion, respiration, and the formation of oxides of nitrogen. * Oxygen is returned to the atmosphere by only one major process: Photosynthesis.
While elemental oxygen ($O_2$) is essential for life, ozone ($O_3$) is a poisonous gas. However, ozone performs an essential function high up in the atmosphere. It absorbs harmful ultraviolet (UV) radiations from the Sun, preventing them from reaching the surface and damaging life forms. * Ozone Depletion: Various human-made compounds like CFCs (chlorofluorocarbons, used as refrigerants) reach the ozone layer and react with ozone molecules, resulting in a reduction of the ozone layer (the "ozone hole").
The Earth's biosphere is sustained by the delicate balance and interaction of the lithosphere, hydrosphere, and atmosphere. Air regulates climate and provides essential gases; water is the fundamental medium for all biological processes; and soil provides the nutrient base for terrestrial life. Elements like water, nitrogen, carbon, and oxygen are continuously recycled through biogeochemical cycles, ensuring that resources are never permanently depleted. However, human activities like pollution, deforestation, and the release of greenhouse gases and CFCs threaten this balance, emphasizing the need for sustainable practices.