Grade 5 Chapter 3: The Earth and its Living World

Introduction

The Earth is a unique planet, characterized by its various spheres: the lithosphere (land), hydrosphere (water), and atmosphere (air). These spheres interact to create the conditions necessary for life. Living things occupy parts of all these spheres, forming what is known as the biosphere. The Sun plays a crucial role in driving many natural processes on Earth, providing the light and heat essential for life.

The Spheres of the Earth

The Earth is composed of several distinct envelopes or spheres:

1. The Lithosphere (Land)

• The Earth's crust is the hard, outermost layer, primarily made of rock.
• We observe layers of soil and rock in hilly regions and along road-cuts.
• Land covers approximately one-third of the Earth's surface.
• It includes vast grassy areas, sandy deserts, and regions covered with crops and forests.
• Tree roots can spread into deeper layers of soil, and sometimes even split rocks apart.
• A vast, continuous stretch of land is called a continent. The Earth has seven continents: Asia, Europe, Africa, North America, South America, Antarctica, and Australia. Asia is the largest, and Australia is the smallest.
• The land is not uniform; it has different shapes and sizes, forming various landforms like plains, hills, mountains, plateaus, valleys, islands, and seashores.

2. The Hydrosphere (Water)

• Water covers approximately two-thirds of the Earth's surface. The lithosphere also extends under this water.
• Most of this water is salty and found in oceans.
• There are five major oceans: the Atlantic Ocean, Pacific Ocean, Arctic Ocean, Southern Ocean, and Indian Ocean.
• The land along the ocean margins is called the coastal region, where various water bodies like seas, bays, straits, gulfs, and creeks are formed.
• Surface Water:
  • Many streams of fresh water flow over the land, ranging from small rills and brooks to larger streams and rivers. Rivers are the biggest.
  • Smaller streams joining a bigger river are called its tributaries.
  • A sudden drop in a river's flow creates a waterfall.
  • Lakes are bodies of water naturally collected in low-lying land areas.
• Water in the form of Ice:
  • In cold regions, water particles in clouds freeze and fall as snow.
  • Layers of snow pile up to form ice. Enormous masses of ice that slip down slopes very slowly are called glaciers.
  • Huge blocks of ice floating in the sea are called icebergs.
• Groundwater:
  • A significant amount of water is stored in underground layers of rock, known as groundwater.
  • We access groundwater through dug wells and bore wells, and many lakes and wells are fed by underground springs.
• The Earth's surface water, ice on land, groundwater, and water vapour in the atmosphere collectively form the hydrosphere.

3. The Atmosphere (Air)

• The envelope of air surrounding the Earth is called the atmosphere.
• As one ascends from the Earth's surface, the air becomes rarer.
• The air is a mixture of gases, primarily nitrogen, oxygen, water vapour, and carbon dioxide, along with other gases in smaller quantities.
• The Earth's surface is heated by the Sun, making the air nearest the surface the hottest; it cools as altitude increases in the troposphere.
• Layers of the Atmosphere: The atmosphere is divided into several layers:
  • Troposphere: Extends up to about 13 km from the Earth's surface. Conditions here change continuously, greatly affecting the living world. Almost all water vapour is contained here, leading to weather phenomena like clouds, rain, fog, winds, and storms. Air on high mountains is rarer, which is why mountaineers and aeroplane passengers need arrangements for sufficient air.
  • Stratosphere: Extends beyond the troposphere, up to about 50 km. It contains the ozone layer, which absorbs harmful ultraviolet rays from the Sun, protecting living things.
  • Mesosphere, Ionosphere, and Exosphere: These are higher layers of the atmosphere.

4. The Biosphere (Living World)

• The biosphere is the part of Earth where life exists.
• Living things occupy parts of the lithosphere, hydrosphere, and atmosphere.
• There are innumerable kinds of living things on Earth, adapted to various regions, whether covered with ice, hot climates, mountains, plains, deserts, salty seas, or freshwater lakes.

The Water Cycle

The water cycle, or hydrological cycle, is the continuous movement of water on, above, and below the surface of the Earth. It involves several key processes:

• Evaporation: Water on the Earth's surface (from oceans, lakes, rivers, soil) continuously turns into water vapour due to the Sun's heat and rises into the atmosphere.
• Condensation: As water vapour rises higher, it cools and condenses, forming tiny water droplets or ice crystals. These droplets are light enough to float, forming clouds.
• Precipitation (Rainfall): As more small droplets join, they form bigger, heavier drops that cannot float. These drops then fall to the Earth's surface as rain. In snow-covered regions, ice melts due to the Sun's heat and flows into rivers.
• This continuous cycle of evaporation, condensation, and rainfall ensures a constant supply of water on Earth.

Summary

• The Earth consists of the lithosphere (land), hydrosphere (water), and atmosphere (air).
• The lithosphere is the Earth's hard crust, including landforms and continents.
• The hydrosphere comprises all water on Earth: surface water (rivers, lakes, oceans), ice (glaciers, icebergs), and groundwater.
• The atmosphere is the envelope of air around Earth, with layers like the troposphere and stratosphere (containing the ozone layer).
• The biosphere encompasses all living things and the parts of the lithosphere, hydrosphere, and atmosphere they occupy.
• The water cycle (evaporation, condensation, precipitation) is a continuous natural process.
• The ozone layer in the stratosphere protects living things from harmful ultraviolet rays.