Lithosphere, Hydrosphere & Atmosphere

Lithosphere, Hydrosphere & Atmosphere

Earth’s Spheres and the Science Behind Them

• The earth comprises three spheres— Lithosphere, Hydrosphere and Atmosphere. These spheres are generally considered as land (soil), water, and air, respectively.
• The study of the lithosphere, hydrosphere, and atmosphere is known as Geomorphology, Oceanography and Climatology, respectively.

• The earth has three spheres: Lithosphere, Hydrosphere, and Atmosphere. The study of these spheres is known as Geomorphology, Oceanography, and Climatology, respectively.
  (Note: The study of the Biosphere, the common life-existing portion of the lithosphere, hydrosphere & atmosphere, is known as 'Ecology'.)

Lithosphere

• The term Lithosphere is the combination of two Greek words: Lithos (= rocky, solid) and Sphaira (= sphere). Thus, the meaning of Lithosphere is solid layers of rock material on the earth's surface, both on the continents and ocean floors.
• Earth's lithosphere constitutes the hard and rigid outer vertical layer of the earth.
• The lithosphere is subdivided horizontally into tectonic plates.
• The lithosphere (or land) covers approx. 29% (exactly, 29.22%) of the total area of the earth.
• The lithosphere is comprised of the crust and the uppermost mantle.

Structure of Earth's Interior

• The Earth's interior is made up of three layers, namely the crust (Sial), Mantle (Sima), and Core (Nife). The crustal layer extends between 30 km and 100 km deep.

Crust (Sial):

The crust is thicker on the continents than on the ocean floors. The crustal layer is of lighter density compared to the interior layers. As the crustal layer comprises rocks rich in Silica and Aluminium, it is called the Sial = (Silica+Aluminium) layer.

Mantle (Sima):

Below the sial layer lies the mantle layer, which extends up to a depth of 2900 km. As the mantle comprises of materials rich in Silica and Magnesium, it is called the Sima = (silica+magesium) layer.

Core (Nife):

The core of the earth consists of metals in a liquid or plastic state of high temperature and pressure. The core of the earth has a radius of 3400 km. As Nickel and Ferrum (the Latin name of Iron) are dominant in the core, it is called the Nife (=Nickel Ferrum) layer. This accounts for Earth's magnetism.

Hydrosphere

• The term "Hydrosphere" is derived from two Greek words: "Hydro" (meaning water or liquid) and "Sphaira" (meaning sphere). Thus, the Hydrosphere refers to the layer of water on the Earth's surface, including oceans, lakes, rivers, and other water bodies.

• The hydrosphere (or water) covers approximately. 71% (exactly 70.78%) of the total surface area of the earth. Therefore, the Earth is sometimes called a watery planet. It is also known as Blue Planet because the Earth appears blue due to water from space.

• Water occurs on the land in the form of ice sheets in the polar region and the form of glaciers on high mountains. Water occurs in the water in the form of liquid water or ice-floes in the oceans and seas. Water also occurs below the surface of the land in the form of underground water. Water also occurs above the surface of the land in the form of water vapor in the lower layers of the atmosphere.

Even flora (plants) and fauna (animals), including man, are predominantly made up of water. This means water is the base of the lives of flora and fauna. That's why it is saying 'Water is life' or 'If there is water there is life' or 'As long as there is water there is life' and so on.

• Out of the total water on Earth, 97% is found in vast oceans as saline water, making it unsuitable for drinking. Only 2% is stored in ice sheets, while less than 1% exists as freshwater, which is non-saline and usable for human consumption. As English poet S. T. Coleridge aptly said, "Water, water everywhere, and not a drop to drink."

• The earth has an abundance of water, but unfortunately, only a small percentage (about 0.3%) is even usable by humans (men). The other 99.7% lies in the oceans, ice sheets, freshwater bodies, and soils (surface water and underground water) and floats in the atmosphere. Still, much of the 0.3% water that is usable is unattainable.

• Most of the water used by humans comes from rivers. The visible bodies of water are referred to as surface water. The majority of water is found underground as soil moisture and in aquifers. Groundwater can feed the streams, that's why a river can keep flowing even when there has been no precipitation. Humans can use both surface and groundwater. Potable water is drinkable water.

Water-Cycle

• The circulation of water among the hydrosphere, atmosphere, and lithosphere is called the water cycle or hydrological cycle.
• Differential heating by the Sun is responsible for the circulation of water in the hydrosphere, similar to the circulation of air in the atmosphere.

• When the surface water in the oceans, seas, rivers, lakes, etc. gets heated by the Sun's rays, evaporation takes place and water vapor is added to the lower layers of the atmosphere. As we know, vapor in the atmosphere may get cooled, leading to condensation of water into tiny droplets which form clouds.

• Such clouds may cause precipitation of water in the form of rainfall or snowfall on the surface. Rainfall on the land leads to surface runoff in the form of rivers, which ultimately reach the oceans.

• In this process of circulation, water is consumed by plants and animals in the biosphere. Water may get temporarily stored on the land in the form of ice sheets, lakes, ponds, or underground water below the land surface.

Atmosphere

• The term Atmosphere is a combination of two Greek words, Atmos (meaning vapor) and Sphaira (meaning sphere). Thus, the meaning of atmosphere is the gaseous envelope that surrounds the earth.

• Among the three major elements of the environment, the atmosphere is the most dynamic as changes take place in it not only from one season to another but also over shorter periods of a few hours.

• Out of the total mass of the atmosphere, 99% is found at a height of 32 km from the earth's surface. It is to be noted that most of the atmospheric changes occur within this layer.

• The atmosphere is held to the earth by the force of gravity.

• The study of the lower layers and upper layers of the atmosphere is known as 'Meteorology' and 'Aerology,' respectively.

Composition of the Atmosphere

• The atmosphere consists of a mixture of gases having a relatively uniform composition in the lower layers. An average sample of pure dry air consists of Nitrogen (78%), Oxygen (21%), and Argon (0.9%); other gases such as Carbon dioxide (0.03%), Hydrogen (0.01%), Helium (0.0005%) and Ozone (0.000001%) are present in minute quantities.
• The lower layers of the atmosphere also contain water vapor in variable quantities. Water vapor is added to the atmosphere by evaporation from oceans, seas, lakes, rivers, ponds, and other water bodies. Though water vapour may not exceed 3% to 4% of the total volume of air at any given place, it plays an important role in the atmospheric process.
• Apart from these gases, solid particles like dust, carbon, salt, pollen grains, etc., are also found in the lower layers of the atmosphere.

Structure of the Atmosphere

• The density of the atmosphere decreases with height.
• There are five layers of the atmosphere: troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere.
  Note: A simple formula to remember layers of atmosphere-

1. Troposphere:

[Tropos (= rotating, changing) + Sphaira (= sphere) = Troposphere]- The lowest layer of the atmosphere is called the Troposphere. In this layer, the temperature of the air decreases with height at an average of 1° C for 165 meters. The troposphere extends up to a height of 8 km along the poles and 18 km along the equator. The upper limit of the troposphere is called the tropopause. Most of the weather phenomena take place in this layer. Due to rotational turbulence that mixes the layers of air and weather phenomena, this sphere is known as the Troposphere.

2. Stratosphere:

[Strato (= layer) + Sphaira (= sphere) — Stratosphere] Above the troposphere is another layer called the stratosphere. The stratosphere extends up to a height of 50 km above the level.
[Sea Level: The sea level is the average level of the sea. It is the base level for measuring elevation (height) and depth on Earth.] In this layer, the temperature remains constant initially and then increases with height. As the stratosphere is free from clouds associated with weather phenomena, conditions are ideal for flying jet aircraft. The ozone in this layer absorbs harmful ultraviolet (UV) radiation from the Sun.

3. Mesosphere:

The term "Mesosphere" comes from the Greek words "Meso" (meaning middle) and "Sphaira" (meaning sphere). It is called the Mesosphere because it is the middle layer between the Stratosphere and Thermosphere. This atmospheric layer extends up to 80 km above the Earth's surface.

4. Thermosphere:

[Thermos (- Heat) + Sphaira (= Sphere) = Thermosphere]. The fourth layer is called the Thermosphere. The thermosphere extends up to a height of about 513 km (according to the National Aeronautics and Space Administration—NASA). Its lower part is called the Ionosphere. In the ionosphere layer, the temperature rises dramatically, reaching up to approximately. 2500°C.

This increase in temperature is because gas molecules present in this layer absorb the ultraviolet and X-rays of the Sun. This results in the breakup of the gas molecules into electrically charged particles called ions.

Charged particles in the ionosphere receive radio waves transmitted from the Earth's surface and then reflect them, enabling wireless and long-distance communication. Different layers of the ionosphere reflect different types of radio waves:

• Long radio waves – Reflected by the D-layer
• Short radio waves – Reflected by the E1, E2, F1, and F2 layers

5. Exosphere:

The term "Exosphere" is derived from the Greek words "Exo" (meaning beyond) and "Sphaira" (meaning sphere). It is the outermost layer of the Earth's atmosphere, located beyond the Thermosphere. Since it extends beyond the main atmospheric layers, it is called the Exosphere. This layer gradually fades into interplanetary space, with no distinct boundary, but scientists estimate it extends up to 10,000 km above Earth.

• The atmosphere is an important element of the environment. The layer of air acts as a blanket or cover protecting the earth from ultraviolet (UV) radiation and extremes of temperature.
• The differential heating of the atmosphere by the Sun's rays produces circulation, leading to cloud precipitation. The variation in climatic conditions on the earth is responsible for diversity in the distribution of plant and animal life.