Air, water and sunlight

Earth has the right conditions for life, but what lets life thrive are the links between living and non-living things. Bring together what you know about air, water, sunlight, soil and minerals, and about life processes in plants and animals, and see how they connect.

The atmosphere holds oxygen, which people, animals and plants all use for respiration. In sunlight, plants take carbon dioxide from the air and water from the soil to make food by photosynthesis, and in doing so they release the oxygen that respiration needs. Each process feeds the other.

Radiation from the Sun heats the Earth, and the atmosphere traps some of that heat through the greenhouse effect. It is mild, but it keeps the temperature just high enough for water to stay liquid. Without an atmosphere, the Earth would lose its heat to space by radiation and become too cold. So the greenhouse effect helps keep the Earth warm. Remember that when the last part of this chapter asks what happens if it gets stronger.

Water is essential for life. It covers about 70 per cent of Earth's surface and is found in ponds, lakes, rivers, springs, seas, oceans and underground. All of it together is called the hydrosphere.

In chapter 7 you learnt that water is a good solvent. In Curiosity, Grade 7, you saw how water carries nutrients from the soil up to a plant's leaves. In animals, water regulates body temperature, aids digestion and keeps the body hydrated, all essential to health and life.

Even though so much of the Earth is water, we still know little about what lives deep in the oceans. The hydrosphere is home to millions of life forms, from tiny plankton to giant whales, and new ones are still being discovered. Oceans, lakes and rivers are rich homes for water life, and fresh water is needed to grow crops and for people everywhere.

Water in the air keeps everything moving. Water vapour forms clouds, which bring rain or snow, which refills rivers, lakes and underground water. Rainfall decides which plants and animals can live in a place, and moving air shapes weather and rainfall, which in turn affect farming, water supply and life on land.