The Four Realms of the Earth Chapter Notes | Footprints Class 6: Book Solutions, Notes & Worksheets PDF Download

Life on Earth thrives due to the harmonious interaction of its three primary realms or domains: land (lithosphere), water (hydrosphere), and air (atmosphere). These realms create the foundation for the Earth's diverse ecosystems and support the existence of various life forms.

1. Land (Lithosphere): The solid outer layer of the Earth, known as the lithosphere, provides the foundation for terrestrial ecosystems. It includes continents, mountains, plains, and soil. Land habitats host a wide range of plants, animals, and microorganisms, each adapted to specific environmental conditions.

2. Water (Hydrosphere): Encompassing all water bodies on Earth, from oceans and seas to rivers, lakes, and groundwater, the hydrosphere plays a crucial role in sustaining life. It provides habitat for aquatic organisms, regulates climate, and influences weather patterns. Water is essential for the survival of all living organisms and is a vital component of various biological processes.

3. Air (Atmosphere): The atmosphere, a layer of gases surrounding the Earth, supports life by providing oxygen for respiration and regulating temperature and climate. It also plays a crucial role in the water cycle, facilitating the movement of moisture and precipitation. The atmosphere contains essential gases such as oxygen, nitrogen, and carbon dioxide, which are fundamental to life processes.

The biosphere is the dynamic interface where these three realms intersect and interact. It encompasses all ecosystems and living organisms on Earth, from microscopic bacteria to towering trees and from deep-sea creatures to soaring birds. Life thrives in the biosphere, where the conditions are optimal for growth, reproduction, and adaptation.

Lithosphere

The Earth's structure resembles layers of an onion, with its outermost shell termed the crust. Below this lies the mantle, followed by the core, which forms the innermost layer. The lithosphere encompasses both the crust and the upper solid portion of the mantle, constituting a sphere of solid rock.

• The term "lithosphere" originates from the Greek word "lithos," meaning rock. It includes continents (approximately 29%) and oceanic crust (about 71%), forming the Earth's solid surface. 
• The lithosphere features diverse physical formations such as mountains, plains, and plateaus, which are crucial for supporting ecosystems and biodiversity.
• These geological features play essential roles in shaping climate patterns, water distribution, and ecological habitats. For instance, mountains influence weather by altering wind currents, while plains provide fertile grounds for agriculture and settlement. Plateaus often host unique ecosystems due to their elevation and geological characteristics.
• In essence, the lithosphere serves as the foundational layer of the Earth's surface, supporting a rich tapestry of life and ecological processes.

Continents

The seven continents (see the map on next page) make up less than one-third of the Earth's surface including big and small land masses. Let us discuss each of the continents in some detail.

• Asia
  • 
    
• Africa
  • .
• North America
  • N
• South America
  • S
• Europe
  • E
• Australia
  • T

Hydrosphere

The hydrosphere includes:

• Oceans
• Seas
• Lakes
• Rivers
• Frozen water
• Underground water
• Water vapor in the atmosphere
• 'Hydro' is the Greek word for 'water'.
• Water covers over 70% of the Earth's surface, earning Earth the nickname "Blue Planet."
• Oceans and seas, which contain saline water, make up 97.3% of the hydrosphere.
• Only 2.7% of the hydrosphere consists of fresh water without salt content.
• Water undergoes cyclical changes within the hydrosphere, known as the hydrological cycle or water cycle.
• Key processes in the water cycle:
  1. Evaporation: Water from oceans, seas, and rivers heats up, turns into water vapor, and rises into the air.
  2. Condensation: Water vapor cools, condenses into tiny water droplets, and forms clouds.
  3. Precipitation: Tiny droplets in clouds combine, grow larger, and fall as rain, snow, or hail.
  4. Precipitation sustains the Earth's fresh water supply.
  5. Precipitation feeds glaciers, rivers, lakes, and underground water sources, eventually returning to the oceans, completing the water cycle.

Oceans

The oceans form the major part of the hydrosphere.

There are five oceans—the Arctic, Atlantic, Indian, Pacific, and Southern Oceans. The five oceans are connected with each other, which means that the level of seawater remains the same everywhere. This is called the sea level.

Pacific Ocean

The Pacific Ocean is the largest ocean and covers more than 30% of the Earth's surface.

• The Earth's deepest point is located here—the Challenger Deep in the Mariana Trench (10,994 m deep).
• Most of the islands of the world are found in the Pacific Ocean (more than 25,000 islands).
• Most of the world's active and dormant volcanoes are also located in the Pacific Ocean basin in a belt called the Pacific Ring of Fire.

Atlantic Ocean

The S-shaped Atlantic Ocean lies between Africa and Europe on its east and North America and South America on its west.

The Equator divides it into the North Atlantic Ocean and South Atlantic Ocean.

This is the saltiest ocean.

Some of the most common natural hazards associated with this ocean are icebergs and hurricanes. Hurricane Katrina in 2005 was one of the most destructive hurricanes ever.

Indian Ocean

The Indian Ocean is mostly in the Southern Hemisphere and between Africa and Australia in East Asia.

The Persian Gulf, Red Sea, and Bay of Bengal are connected to this ocean.

India lies at its head.

It is important for travel and trade between Europe and Asia.

Arctic Ocean

The Arctic Ocean is the smallest of the world's five oceans.

The Northwest Passage (US and Canada) and the Northern Sea Route (Norway and Russia) are two important seasonal waterways.

During winters, this ocean is frozen. However, the ice melts and forms large icebergs and floating islands during summers.

Southern Ocean

The Southern Ocean is located around the South Pole across the Antarctic Circle in the Southern Hemisphere.

• Atmosphere
  • Earth's realm of air is the atmosphere, bound by Earth's gravity.
  • Extends nearly 10,000 km above Earth, then transitions to airless space.
  • Air composition changes with altitude, affecting breathing.
  • Layers: Troposphere (8-16 km, weather effects), Stratosphere (ozone layer, UV protection), Mesosphere (meteor burn-up), Thermosphere/Ionosphere (important for communication, satellite placement), Exosphere (space station location).
  • Importance: Maintains Earth's temperature, exerts pressure, influences air movements like winds.
• Biosphere
  • Interaction of land, water, and air forms the biosphere.
  • Life exists in a narrow belt on or near land/water surfaces, surrounded by air.
  • Biosphere hosts a variety of life forms, creating ecosystems.
  • Ecosystems balance biotic (living) and abiotic (non-living) elements.
  • Nature's balance is key; disruptions like urbanization and pollution impact ecosystems.
  • Human actions affect nature's balance; sustainable planning is crucial for future resource preservation.