Earth- A living Planet
- The Earth is the only known planet in the universe that supports life. That is why we also call it the living planet.
- Sun is the main source of energy that drives all forms of life and associated processes on the Earth.
- We may think of the Earth as a geosphere that has four main components which are:
- Lithosphere – Solid land mass
- Atmosphere – Envelope of air
- Hydrosphere – Body of water
- Biosphere – All life on Earth
- Geosphere is a kind of umbrella term exhibiting all these four vital components of the planet Earth.
- The Lithosphere:
- The lithosphere provides suitable and stable piece of landmass. This stable landmass is arranged into several topographical features such as mountains, hills, plains and plateaus etc.
- These landforms make a part of the physical environment in geosphere. The lithosphere provides suitable habitat for various forms of life.
- It is the source of soil, sediment, salts of the sea and nutrients.
- Lithosphere consists of the crust and upper parts of the mantle.
- Crust can be divided into two parts, viz., continental and oceanic crust.
- The average thickness of the lithosphere is about 100 kilometres. However, it significantly differs between the oceans and continents. The thickness varies from only a few kilometres over the oceanic parts of the lithosphere to around 300 kilometres under the continents.
- Lithosphere is composed of different types of rocks such as igneous, sedimentary and metamorphic rocks.
- The Atmosphere:
- The atmosphere envelops the Earth and is made up of various gases, water and dust particles. The main gases present in the atmosphere are nitrogen and oxygen having a share of nearly 75 and 23 percent. Other gases are argon, CO2, helium etc.
- The amount of these gases in the atmosphere decreases as we move away from the Earth. Almost the entire atmosphere constituting about 97 percent extends upto 30 kilometres from the Earth’s surface. Its upper limit is at approximately 1000 kilometres.
- The space beyond this distance (about 100 kilometres) is generally referred to as extra-terrestrial space.
- The Hydrosphere:
- We call the earth a blue planet because of the presence of large amounts of water on it.
- Water is present in three states gaseous (water vapour in the atmosphere), liquid (running water on the surface and underground water beneath the surface) and solid (ice caps).
- Water present in the Earth’s surface is mainly of two kinds:
- Fresh water (about 3%), stored in the glaciers, lakes, streams and underground.
- Salt water (about 97%), stored in seas and oceans.
- All these forms of water are dynamic in nature. Water is stored in glaciers, lakes, rivers, seas and oceans etc.
- The sphere which stores enormous amounts of water as ice in frozen state is known as cryosphere (subcomponent of hydrosphere).
- How does the cryosphere affect global climate? [UPSC, 2017]
- The stored water in its liquid state evaporates into the atmosphere and, falls back in the form of precipitation (rain, snow and hailstorm etc.) on the Earth’s surface. Then, it flows back to the various water bodies. This process of evaporation and precipitation is continuous. It is called the ‘hydrological cycle’.
- Water in oceans, seas, rivers and streams is also responsible for changing and creating various landforms. For example, the rocks on sea beaches are constantly sculptured by water waves resulting into formation of various landforms like cliffs and sea caves etc.
- Water is essential for various forms of life. Even our body is composed of nearly 75% water. The hydrosphere is a source of the huge amounts of water needed for agriculture, industry and other economic activities.
- The Biosphere:
- The lithosphere, atmosphere and hydrosphere are inorganic or non-living components of the geosphere. The organic or living component is called the biosphere. It also includes those parts of the lithosphere, atmosphere and hydrosphere that provide the physical environment.
- All life forms have evolved in a narrow zone in the biosphere. It includes plants, animals and all other living things. These life forms are not independent as they share complex relationship with the other three components of the geosphere.
- For example, the oxygen we breathe is provided by the atmosphere; the water we drink comes from the hydrosphere and the geographic area where we live is on the lithosphere. Thus, together the other three components provide the physical environment that supports all life forms.
- Life is mostly confined in a narrow zone of the geosphere. It is concentrated between the lowest layers of the atmosphere and the ocean bottoms in the biosphere. More than three-fourths of the all life forms are concentrated here.
- However, there is an exception to this like coral reef that develops in the deep ocean floor, bacterias that thrive and live on deep parts of the rock layers beneath the Earth’s surface up to 4 kilometres.
- All the four components of geosphere namely lithosphere, atmosphere, hydrosphere and biosphere are linked to each other for the exchange of energy and material. They co-exist and one cannot function without the help of other.
- The biosphere quintessentially regularly alters the character and form of lithosphere, atmosphere and hydrosphere. It is the only lively component that renders a definite purpose to the other three non-lively components.
