Earth’s Spheres & Structure - Environment

Earth’s Spheres & Structure - Environment

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.

Note: The study of the Biosphere, the common life-existing portion of the lithosphere, hydrosphere & atmosphere, is known as 'Ecology'.

Lithosphere

Meaning of Lithosphere

The term Lithosphere is the combination of two Greek words:

• Lithos (= rocky, solid)

• Sphaira (= sphere)
  Thus, the meaning of Lithosphere is solid layers of rock material on the Earth's surface, both on the continents and the ocean floors.

Key Characteristics

• 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 approximately. 29% (exactly, 29.22%) of the total area of the Earth.

• It is comprised of the crust and the uppermost mantle.

Structure of Earth's Interior

Main Layers

• 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.

Core Mantle (Sima)

• Below the sial layer lies the mantle layer, which extends up to a depth of 2900 km.

• As the mantle comprises materials rich in Silica and Magnesium, it is called the Sima = (Silica + magnesium).

Core (Nife)

• The core of the Earth consists of metals in a liquid or plastic state at 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

Definition and Etymology

• 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.

Earth's Water Coverage

• 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 the Blue Planet because the Earth appears blue due to the water from space.

Forms and Presence of Water

Water occurs:

• On the land in the form of ice sheets in the polar region and glaciers on high mountains.

• In oceans/seas, as liquid water or ice floes.

• Below the land surface is underground water.

• Above the surface, in the atmosphere as water vapor.

Water and Life

Even flora (plants) and fauna (animals), including man, are predominantly made up of water.

• This means water is the basis of life.

• That's why it is said

  • "Water is life", or

  • "If there is water, there is life", or

  • "As long as there is water, there is life" and so on.

Distribution of Water

Out of the total water on Earth:

• 97% is found in vast oceans as saline water, unsuitable for drinking.

• 2% is stored in ice sheets.

• Less than 1% exists as freshwater, 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 only about 0.3% is usable by humans.

The other 99.7% lies in oceans, ice sheets, freshwater bodies, soils, and floats in the atmosphere. Still, much of the 0.3% water that is usable is unattainable.

Sources of Water for Humans

Most of the water used by humans comes from rivers, called surface water.

• The majority is found underground as soil moisture and in aquifers.

• Groundwater can feed streams, which is why rivers flow even without precipitation.

• Humans can use both surface and groundwater.

• Potable water = drinkable water.

Water-Cycle

Definition

• The circulation of water among the hydrosphere, atmosphere, and lithosphere is called the water cycle or hydrological cycle.

Process and Importance

• The sun's heat causes evaporation from water bodies.

• Water vapor rises and condenses into clouds.

• Clouds cause precipitation (rain/snow).

• Rainfall leads to surface runoff (rivers), returning water to the oceans.

• Water is consumed by plants and animals in the biosphere.

• Water is also stored temporarily as ice sheets, lakes, ponds, or underground water.

Atmosphere

Definition and Etymology

• The term Atmosphere is a combination of two Greek words: Atmos (meaning vapor) and Sphaira (meaning sphere).

• Thus, the atmosphere is the gaseous envelope that surrounds the Earth.

Dynamic Nature

• Among the three major elements of the environment, the atmosphere is the most dynamic, changing over seasons and even hours.

• 99% of the atmosphere’s mass is found within 32 km of Earth’s surface.

• Most atmospheric changes occur within this layer.

• The atmosphere is held to the Earth by gravity.

• The study of:

  • lower layers: Meteorology

  • upper layers: Aerology

Composition of the Atmosphere

Gases in the Atmosphere

The atmosphere consists of a mixture of gases in uniform composition in the lower layers.

• Pure dry air consists of:

  • Nitrogen (78%)

  • Oxygen (21%)

  • Argon (0.9%)

• Minor gases:

  • Carbon dioxide (0.03%)

  • Hydrogen (0.01%)

  • Helium (0.0005%)

  • Ozone (0.000001%)

Water Vapour and Solids

Water vapor is added via evaporation from water bodies.

• It plays a vital role in atmospheric processes even though it doesn't exceed 3–4% of the air volume.

• Solid particles like dust, carbon, salt, pollen grains, etc., are also present.

Structure of the Atmosphere

Decreasing Density

The density of the atmosphere decreases with height.

There are five layers of the atmosphere:

1. Troposphere

2. Stratosphere

3. Mesosphere

4. Thermosphere

5. Exosphere
   (Tip: Use mnemonic formulas to remember layers.)

1. Troposphere

[Tropos = (rotating, changing)] + [Sphaira = (sphere)]

• The lowest layer of the atmosphere.

• Temperature decreases by 1°C for every 165 meters.

Extends up to:

• 8 km at the poles

• 18 km at equator

  • Upper limit: Tropopause

• Most weather phenomena occur here.

• Due to turbulence and mixing, it's called the Troposphere.

2. Stratosphere

[Strato = (layer)] + [Sphaira = (sphere)]

• Above the troposphere, it extends up to 50 km.

• Initially, the temperature remains constant, then increases.

• Ideal for jet aircraft — no clouds or weather.

Contains the ozone layer, which absorbs UV radiation.

3. Mesosphere

Derived from Greek: "Meso" = middle, "Sphaira" = sphere

• Middle layer between the Stratosphere and the Thermosphere

• Extends up to 80 km above Earth.

4. Thermosphere

[Thermos = (Heat)] + [Sphaira = (Sphere)]

• Extends up to 513 km (as per NASA).

• The lower part is the Ionosphere.

• The temperature reaches approx. 2500°C due to UV and X-ray absorption.

• Gas molecules split into ions.

These ions reflect radio waves:

• Long radio waves → D-layer

• Short radio waves → E1, E2, F1, F2 layers

5. Exosphere

[Exo = beyond] + [Sphaira = sphere]

• Outermost layer of the atmosphere, above the Thermosphere

• Gradually fades into interplanetary space

• No defined boundary, but extends up to 10,000 km

Importance of the Atmosphere

• 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.

• Differential heating causes air circulation, leading to cloud formation and precipitation.

• These climatic variations result in diverse plant and animal life on Earth.

Final Thoughts

The study of the Earth’s spheres—the Lithosphere, Hydrosphere, and Atmosphere—offers a comprehensive understanding of how our planet operates as an interconnected system. The Lithosphere provides the solid, rocky foundation of the Earth, supporting both landforms and human civilization. The Hydrosphere, covering around 71% of the Earth's surface, plays a crucial role in sustaining life through its vast reservoirs of surface and underground water.

The Atmosphere acts as a protective shield, regulating temperature, enabling weather, and supporting life by supplying oxygen and filtering UV radiation. Together, these spheres interact through natural processes like the Water Cycle, illustrating the seamless exchange of energy and matter.

Understanding these systems is not only essential for academic disciplines such as Geomorphology, Oceanography, Climatology, and Ecology, but also for promoting environmental awareness, sustainability, and the responsible use of natural resources in today’s changing world.