Water in the Atmosphere Chapter Notes | Science for Grade 6 PDF Download

Introduction

Water is all around us, not just in oceans, rivers, and lakes, but also in the air, clouds, and even inside living things like plants and animals. This chapter, "Water in the Atmosphere," explores how water moves through Earth's systems, especially the atmosphere. You’ll learn how water changes from liquid to gas, forms clouds, and comes back as rain or dew. By understanding these processes, you’ll see how water cycles through our planet and why it’s so important for life.

Where is water on earth?

• Earth is called the blue planet because most of its surface is covered with water.
• Water is found in oceans, clouds, air, underground, and inside living organisms like plants and animals.
• Water moves through four subsystems of Earth: atmosphere (air), biosphere (living things), geosphere (land), and hydrosphere (water).
• These subsystems work together to distribute water across the planet.
• Water moves from one subsystem to another, like from oceans to the atmosphere or from plants to the air.

What influences why and how quickly water "disappears"?

• Water in puddles or clouds seems to vanish but actually changes into a gas through a process called evaporation.
• Evaporation happens when the Sun heats water, giving it energy to turn into water vapor, an invisible gas in the air.
• Sunlight or heat makes water evaporate faster, like when puddles dry up quicker in the sun than in the shade.
• Water vapor rises into the atmosphere after breaking away from liquid water molecules.

How else can water enter the atmosphere?

• Most water vapor (90%) comes from oceans, rivers, lakes, puddles, and soil through evaporation.
• Plants release water vapor through a process called transpiration, where water moves from roots to leaves and into the air.
• Transpiration happens more when plants have lots of water or when the air is warm.
• Animals release water vapor through breathing during cellular respiration, a process where food breaks down and releases water and carbon dioxide.
• When plants and animals die, the water stored in their tissues returns to the environment as they decompose.

How can you get water to "reappear"?

• Water vapor in the air can turn back into liquid water through a process called condensation.
• Condensation happens when water vapor cools, like when dew forms on grass in the morning or water droplets appear on a cold glass.
• As water vapor rises in the atmosphere, it cools because temperatures decrease with height.
• Cooled water vapor condenses into tiny droplets or forms ice crystals, which can create clouds or fog.
• Crystallization is when liquid water turns into ice crystals, which happens when water loses a lot of thermal energy.
• Condensation and crystallization release energy, unlike evaporation, which absorbs energy.
• Clouds form when thousands of water droplets or ice crystals group together, blocking and reflecting light to become visible.

A Closer Look: Solar Halos

• A solar halo is a circular rainbow around the Sun, seen when high, thin cirrus clouds are present.
• Cirrus clouds form 6,100 meters or higher above Earth and are made of tiny ice crystals.
• Water vapor in the atmosphere condenses and then crystallizes into ice at high altitudes.
• Light passing through these ice crystals bends, a process called refraction, creating a rainbow-like effect.
• The halo sparkles because light also reflects off the ice crystals, like sunlight reflecting off a mirror.
• The Sun and ice crystals must be in the right position for a solar halo to be visible.
• Clouds are classified into three main groups based on the height of their bases: high clouds (like cirrus), mid-level clouds, and low clouds.