Water on Earth’s Surface Chapter Notes | Science for Grade 6 PDF Download

Introduction

The chapter "Water on Earth's Surface" explores how water moves and changes on our planet as part of the water cycle. It explains how water travels from clouds to streams, aquifers, and other places like oceans, lakes, and glaciers. You will learn about the different forms water takes, such as liquid, vapor, and ice, and the forces like gravity and the Sun's energy that drive its movement. The chapter also discusses how water is stored in reservoirs like groundwater and ice sheets and how changes in Earth's temperature can affect the water cycle. This helps us understand why water is so important and how it keeps moving around Earth.

Why do some clouds rain?

• The Sun's energy heats water on Earth's surface, causing it to turn into water vapor (evaporation).
• Water vapor rises into the air, cools, and turns back into liquid or solid form (condensation or crystallization), forming clouds.
• Precipitation happens when water falls from clouds as rain (liquid) or as snow, sleet, or hail (frozen).
• Not all clouds produce precipitation; it depends on conditions like how much water the cloud holds.

Did You Know?

Water moves between Earth's surface and the atmosphere in a process called the water cycle. The total amount of water on Earth stays the same, but its movement can change. Changes in Earth's global temperature affect how water moves in the water cycle.

Climate Change: Trends & Patterns

• Climate change is shifting where and how much rain falls around the world.
• Wet areas may get wetter, and dry areas may get drier, causing more extreme weather like storms.
• The Intergovernmental Panel on Climate Change (IPCC, 2011) says rising global temperatures change precipitation and moisture in the air.
• Warmer air in the lower atmosphere (troposphere) increases evaporation, leading to more moisture in the air.
• More moisture can cause heavier rain and flooding in some areas.
• In other areas, warmer temperatures can cause more drying, leading to droughts.
• Scientists use computer models with global data to predict how climate change affects the water cycle.
• The Global Precipitation Measurement mission (GPM) helps measure water movement, clouds, and precipitation to improve climate models.

Where does all the rain go?

• Precipitation is pulled to Earth's surface by gravity.
• More than 75% of precipitation falls into the ocean.
• The rest falls on land, where some evaporates back into the atmosphere.
• Some water flows into lakes or streams, which eventually flow back to the ocean.

Where is water stored?

• Water is stored in reservoirs, which are places like oceans, lakes, glaciers, ice caps, and groundwater.
• Water is always moving in the water cycle, but it stays in these reservoirs for long periods.

Water Under Your Feet

• Groundwater is water found below Earth's surface.
• Aquifers are areas of rock or sediment that hold a lot of water in tiny spaces (pores).
• Water seeps through soil into these pores to become groundwater.

Groundwater Flow

• Groundwater flows from higher to lower elevations, eventually reaching the ocean.
• In some places, groundwater is close to the surface, keeping soil wet.
• In dry areas like deserts, groundwater can be hundreds of meters underground.
• Groundwater can come to the surface as springs, creating oases in deserts where plants grow.
• Groundwater can flow into streams, lakes, or wetlands, becoming surface water.
• Surface water can seep into the ground to replenish groundwater.

Did You Know?

Oases, the green and fertile spots in deserts, are created when underground water rises close to the surface. This causes springs to form, turning dry land into places where plants can grow. In lower areas of Earth's surface, groundwater can seep out and flow into lakes, streams, or wetlands—becoming surface water. In the same way, surface water can soak into the ground and become groundwater again. This back-and-forth process helps keep groundwater levels steady.

Water in Glaciers and Ice Sheets

• Water can freeze and form glaciers or ice sheets, which are large masses of ice.
• Snow falls and builds up over years, not melting.
• The weight of new snow presses down on older snow, turning it into ice.
• Over time, the heavy ice flows downhill like a slow-moving river due to gravity.
• This process can take over 100 years for most glaciers.

Did You Know?

When snow keeps falling each year without melting, it starts to build up in layers. The weight of the upper layers presses down on the lower ones, slowly turning the bottom snow into ice. As more snow and ice pile up, the entire mass becomes so heavy that gravity pulls it downhill, creating a slow-moving river of ice called a glacier. For most glaciers, this incredible process takes more than a hundred years to happen!