Cycling of Matter

Introduction:

Have you ever looked at the sky and wondered what the sky and the ground have in common? Both the sky as well as the ground are constantly undergoing changes. Some of these changes on the Earth are slow, while some are fast. Some changes are driven by Earth’s internal energy, while others are driven by energy that comes from the sun. Together these changes are a part of Earth’s systems.

Explanation:

Earth is the third planet in our solar system. It is the only planet that has abundant liquid water on its surface. About 71% of the Earth’s surface is covered by water, and this water is known as the global ocean. It forms a major portion of the hydrosphere.

The Earth has four major systems between which the cycling of energy and matter takes place. These four systems together form the Earth system.

The cycling of matter and energy between these four systems makes life on Earth possible. These four systems consist of:

• Geosphere
• Atmosphere
• Hydrosphere
• Biosphere

Geosphere:

The geosphere is the part of the planet that comprises solid rock and minerals. It is divided into layers based on chemical composition and physical properties.

The compositional layers divide the Earth into three types which include the solid crust, the molten mantle, and the liquid and solid parts of the Earth’s core.

The crust is the thin, outermost layer of the Earth and is composed largely of silicon, aluminum, and oxygen. The mantle lies between the core and the crust of the Earth. It is a hot layer of rock made up of denser silicate materials. The central portion is the core, and it is made up of iron and nickel.

Based on physical properties, Earth can also be divided into five layers which are as follows:

Lithosphere: It is the outermost, cold, and brittle layer that can be divided into pieces called tectonic plates.

Asthenosphere: It is a solid, plastic layer on which the tectonic plates move. It resembles putty.

Mesosphere: It is the solid lower layer of the mantle.

Outer core: It is made of liquid iron and nickel.

Inner core: It is also comprised of iron and nickel but in solid form.

In most places, the geosphere forms a layer of soil in which nutrients become available to living organisms. This helps in forming the basis of many life forms and provides an important ecological habitat.

The surface of the geosphere is subjected to processes of erosion, weathering, and transport, as well as to tectonic forces and volcanic activity. This results in the formation of landforms such as mountains, hills, and plateaus.

Atmosphere:

The atmosphere is the gaseous layer surrounding the earth and held to its surface by gravity. The atmosphere extends outward to about 500km from the Earth’s surface. However, most of the atmospheric gases lie between 8-12 km from the Earth’s surface.

The atmosphere comprises four layers: the troposphere, stratosphere, mesosphere, and thermosphere.

Energy flow in the atmosphere:

Sun is the major source of energy that reaches the Earth’s surface. Solar radiation unevenly heats the surface of the earth. This uneven heating is responsible for the movement of air in the atmosphere. For example, cold air is denser than warm air, and as a result, it tends to sink into the atmosphere.

As the cold air sinks, it pushes the warmer air out of its way. This movement of air distributes energy throughout the atmosphere. In this case, heat energy is transferred throughout the atmosphere due to the movement of air, and this process is called convection.

Hydrosphere:

The hydrosphere consists of water in, on, and surrounding the Earth. It consists of liquid, gaseous as well as solid phases. The hydrosphere includes water present in the Earth’s oceans and seas, glaciers, lakes, rivers, and streams. Clouds, rain, and snow are also a part of the hydrosphere.

The hydrosphere includes both saltwater and freshwater systems, and it also includes the moisture found in the soil and within rocks.

Energy flow in the hydrosphere:

The energy from the sun unevenly heats the ocean water. This causes variations in the temperature of the ocean. The temperature of ocean water is warmer at the equator and freezing near the poles. The temperature also tends to decrease with depth.

These differences in temperature cause differences in density which leads to the movement of water by convection. This movement of matter caused by differences in density is called convection current and helps distribute energy in the ocean.

Biosphere:

The biosphere contains all living organisms and areas of Earth where life is found. It is intimately related to the other three spheres as it includes the Earth’s surface, the lower layer of the atmosphere, and most of the hydrosphere.

The biosphere has certain factors that living organisms require, for example, gases from the atmosphere, water from the hydrosphere, and nutrients and minerals from the geosphere.

In a biosphere, most plants and animals are able to survive only in environments that have moderate temperatures. A stable energy source is also present in a biosphere and is essential for living organisms. For example, plants and algae obtain energy from the sun to prepare their food.

Energy flow in the biosphere:

Energy enters the biosphere in the form of sunlight. Plants use this energy and change it to chemical energy through the process of photosynthesis. This energy is then passed to animals that eat plants. As animals eat other animals, this energy keeps getting transferred between organisms.

The transfer of energy does not stop when an organism dies, as dead organisms are consumed by decomposers like bacteria and fungi. These decomposers break down the remains into simpler materials like CO₂, which are used by plants during photosynthesis.

Biogeochemical cycles:

All the matter that we find on Earth results from the continuous cycling of Earth’s materials. Very little new matter enters the Earth’s system. As matter circulates between the Earth, the atmosphere, and biotic factors, it keeps changing.

Water, carbon, nitrogen, phosphorous, and even rocks pass through cycles continuously in order to support life on this planet.

These cycles are also known as biogeochemical cycles and include:

• The hydrological cycle
• The carbon cycle
• The nitrogen cycle
• The phosphorous cycle

The hydrological cycle, also known as the water cycle, is the continuous movement of water between the atmosphere, land, and oceans. The major source of energy that powers the water cycle comes from the sun.

This energy from the sun heats the water on Earth and causes water to change its state. For example, liquid to the vapor state. The water cycle is carried out in four major steps.

The first step is evaporation, in which liquid water changes into a gaseous vapor due to the heat from the sun. Water vapor is also released into the atmosphere through the pores on the leaves of plants. This process is also known as transpiration.

If the air containing water vapor cools, the water vapor turns into liquid water droplets and leads to the formation of clouds.

This change from gas to liquid is called condensation. When the droplets accumulate and become large enough, they fall back on the Earth as precipitation in the form of rain.

Most precipitation falls directly into the ocean and never reaches the land surface. Precipitation that reaches the Earth’s surface may fill lakes, streams, and rivers and then eventually flow back to the ocean.

The water that moves over the land surface is called run-off. Some of the water may move downward through spaces in rock or soil as a result of gravity, this water later becomes groundwater.

Like water, certain elements are also essential to support life on Earth. Sometimes, these elements become part of the cells of living organisms as nutrients. At other times these nutrients exist as abiotic factors of the environment.

The nitrogen, phosphorus, and carbon cycles explain how the cycling of matter takes place in both biotic and abiotic factors of the environment. These cycles also explain how matter and energy flow into the ecosystem in the form of food webs or food chains.

These cycles are essential for the survival of all lifeforms on Earth.

Nitrogen cycle

Phosphorus cycle