Spheres of Earth-Biogeochemical cycles

Introduction:

Earth is the place where we live. It is the third planet from the sun. 70% of Earth is covered by water. The planet Earth is made of sub-systems called spheres. There are 5 spheres on the Earth. They are the geosphere, atmosphere, hydrosphere, biosphere, and cryosphere. All the spheres of Earth interact with each other. Earth’s spheres do not work individually.  The action of one sphere affects the other sphere. Humans can have major effects on various spheres of the Earth. For example, the burning of fossil fuels causes a lot of air pollution(atmosphere). Dumping waste into water bodies causes water pollution (hydrosphere). Accumulation of waste in landfills disturbs the geosphere. All these effects finally disturb the ecosystem (biosphere).

The geosphere is also known as the lithosphere. All the natural forms, such as mountains, oceans, glaciers, hills, valley, canyons, sand dunes, plains, and plateaus, present on the  Earth’s land constitutes the lithosphere. These natural forms are called landforms.

The hydrosphere includes Earth’s water. 97% of the Earth’s water is salt water present in the oceans. Freshwater is present in aquifers, lakes, rivers, and glaciers. Earth’s water always moves through a water cycle. Water evaporates from the surface of the earth into the atmosphere in the form of gas. In the atmosphere, water condenses and forms clouds. As the number of water droplets increases in the clouds, it falls back to the earth as rain, sleet, hail, or snow (precipitation). Then some water flows into lakes, rivers, and oceans, whereas some water seeps into the soil and ground.

Atmosphere: The blanket of air around the earth is called the atmosphere. The atmosphere is a mixture of gases. A major area of the atmosphere is covered by nitrogen (78%), oxygen (21%), and other gases (1%). The other gases include water vapor and carbon dioxide, which are essential for the earth’s water cycle. Earth’s atmosphere comprises different layers. The layer closest to the earth is the troposphere. In this region, the air is always on the move and the wind is a gentle breeze. Weather changes by changes in wind direction.

Biosphere: It includes all living things on the earth such as plants, animals, fungi, and microscopic plankton. Life on Earth is close to all the spheres of Earth, where it can use oxygen(atmosphere), carbon dioxide (atmosphere), sunlight (atmosphere), water (hydrosphere), minerals (lithosphere), and organic matter (lithosphere). Between the land, water habitat, and ocean, the biosphere is divided into biomes. A biome is a place on the earth that depends upon rainfall and temperature and helps living things to grow well in that habitat.

Cryosphere: There are some places on Earth that are very cold where water is present in a frozen solid state. These areas of snow or ice are the areas where the temperatures fall below 0°C (32ﹾF) for at least some part of the year. So, the cryosphere is the solid (frozen) part of the earth’s system.

One part of the cryosphere is ice and snow. This comprises the largest parts of the cryosphere, the continental ice sheets that are found in Greenland and Antarctica. Also, ice caps, glaciers, and areas of snow and permafrost are as well found in these regions. When continental ice melts and flows from land and goes to the sea surface, we get shelf ice.

There is also ice that is found in water in the other part of the cryosphere. This comprises of frozen parts of the ocean, such as waters encircling Antarctica and the Arctic. It also comprises frozen rivers and lakes that primarily occur in polar regions.

The elements of the cryosphere play a significant role in the Earth’s climate. Snow and ice reflect heat from the sun, which helps to regulate the Earth’s temperature.

Biogeochemical Cycles

There are some types of atoms that can be a part of a plant, an animal, part of a river’s water, etc. These atoms can be a part of both living things as well as non-living things such as water, air, and even rocks. So, the same atoms are recycled over and over in several parts of the Earth. This kind of cycle of atoms between living and non-living things is known as a biogeochemical cycle.

The biogeochemical cycle consists of all the atoms that are building blocks of living things. The carbon cycle and nitrogen cycles are the most common cycles.

Small atoms of carbon and nitrogen are able to move around the Earth all the way through these cycles. For example, ocean water absorbs an atom of carbon from the air, and it is used by tiny floating plankton in the process of photosynthesis to prepare food. There is a chance that this tiny carbon atom becomes part of the plankton’s skeleton or a part of the large animal’s skeleton that eats plankton. Hence when the living things die and only bones are left behind, it becomes part of sedimentary rock.

Carbon that is a part of rocks and fossil fuels such as oil, coal, and natural gas may be held away from the rest of the carbon cycle for a long time. These long-time storage areas are called “sinks.” When we burn fossil fuels, carbon that had been present underground is sent into the atmosphere as carbon dioxide, which is a greenhouse gas.

The Carbon Cycles

The carbon cycle can be very easily understood by two interconnected sub-cycles:

• One carbon cycle deal with the rapid exchange of carbon among living things.
• The second carbon cycle deals with the long-term cycling of carbon through various geologic activities.

The carbon element is a component of seawater (Hydrosphere), the air (Atmosphere), soils (Geosphere), all living things (Biosphere), and rocks like limestone and coal (Geosphere). On Earth, carbon is able to move from one of these spheres to another as a part of the carbon cycle.

The Biological Carbon Cycle :

• From the atmosphere, carbon goes to the plants. In the atmosphere, carbon is attached to oxygen gas in the form of carbon dioxide (CO₂). By the method of photosynthesis, carbon dioxide gas from the air is absorbed by the plant, to produce food for the growth of plants.
• Carbon moves from plants to animals through the food chain.

• From plants and animals [Biosphere], carbon moves to soil [Geosphere]. After the death of plants and animals, their bodies, wood, and leaves, decompose and bring the carbon into the ground. In millions and millions of years, some dead and decayed plants and animals get buried and become fossil fuels.
• The movement of carbon is from living things [Biosphere] to the atmosphere. Every time when animals exhale, the carbon dioxide gas (CO₂) is released into the atmosphere. Plants and animals need to get rid of carbon dioxide gas by the process of respiration.
• When fuels are burned, carbon moves from fossil fuels to the atmosphere. Most of the carbon quickly enters the atmosphere as carbon dioxide gas by burning fossil fuels to power factories, power plants, cars, and trucks. Every year, five and a half billion tons of carbon are released into the atmosphere by burning fossil fuels. From this huge amount, 3.3 billion tons stays and the remaining CO2 dissolves in seawater.
• Carbon goes from the atmosphere to the oceans (Hydrosphere). The oceans and other water bodies absorb a certain quantity of carbon from the atmosphere and that carbon gets dissolved into the water.

The Geological Carbon Cycle:

The geological carbon cycle takes more time than the biological carbon cycle. Generally, it takes millions of years for carbon to cycle through the geological pathway. Carbon may be stored for a long time in the atmosphere, water bodies – mostly oceans— ocean sediment, soil, rocks, fossil fuels, and the interior of Earth.

The level of carbon dioxide in the atmosphere is affected by the carbon reservoir in the oceans and vice versa. Carbon dioxide present in the atmosphere dissolves in water and reacts with water molecules as shown in the following reactions:

CO₂​+H₂​O⇌H₂​CO₃​⇌HCO₃⁻​+H⁺⇌CO₃²⁻​+2H⁺

The carbonate released in this process combines with calcium ions to form calcium carbonate. It is a major part of the shells of marine organisms. After the death of the organisms, their bodies may sink and ultimately become part of the sediment on the ocean floor. Over a period of geologic time, the sediment converts into limestone, which is the biggest reservoir of carbon on Earth.

On land, carbon is stored in the soil as organic carbon obtained by the decomposition of living things or as inorganic carbon by weathering of rock and minerals present on the ground. Fossil fuels are present deeper inside the ground such as oil, coal, and natural gas. These are the remains of plants decayed under anaerobic (in the absence of oxygen). The formation of fossil fuels takes millions of years to form. When humans burn fossil fuels, carbon is given out into the atmosphere in the form of carbon dioxide.

There is another way for carbon to enter the atmosphere is by volcanic eruptions. On the ocean floor, carbon-containing sediments are taken deep within the Earth by a process called subduction. In this process, one tectonic plate moves under another and forms carbon dioxide, which can be given out into the atmosphere by volcanic eruptions or hydrothermal vents.