Earth is called the blue planet due to the abundance of water. About 70% of the surface of the Earth is covered by water, and it is the only natural substance that can be found on Earth in all three states – liquid, solid and gas. Due to this unique property1, water can be found just about everywhere.
Liquid, solid and gas
Rivers, groundwater2, lakes, the world’s five oceans and rain represent the liquid phase of water.
Dynamic and complex: the global water cycle
Water in the Earth system is influencing all aspects of life on Earth. Pathways, storage, transfers and transformations have an effect on the global climate and human welfare. Within this interactive 4 scientists talk about some of the complex aspects of the water cycle.
To use this interactive, move your mouse or finger over any of the labelled boxes and click to obtain more information.
Select here to view the full transcript and copyright information.
In its gaseous state, water vapour3 is evaporated by the Sun’s solar radiation4 from the surface of water bodies like oceans or lakes, and from the surface of plants and the land. Water vapour can also evaporate directly from its frozen state.
Snow and ice represent the solid form of water and can be found in the Earth’s polar icecaps and on top of high mountains. Some of the snow and ice melts and turns into liquid water. In the polar regions, ice can stay frozen for thousands of years.
Only a small amount of the total amount of water (about 0.3%) is directly useable for human consumption.
Water’s journey
David Hamilton testing water
Professor David Hamilton measures temperature, oxygen and algal concentrations in the water. When David studies lakes in New Zealand, he needs to think about where the water came from before it entered a lake and what influences the land around the lake has on water quality.
If you leave some water on a saucer by a window, it will eventually evaporate. This happens only if there is enough thermal (heat5) energy available for the water molecule6 to vibrate so vigorously that the molecules7 ‘break’ out of their liquid structure and turn into a gas.
But why do the oceans not dry up? In fact, most of the evaporation8 occurs from ocean water. Much of the evaporated water rains back into the oceans again. Some falls on the land surface and might spend some time on there as ice, snow, groundwater or in streams, or it may be stored in lakes before it returns back to sea.
This journey is called the hydrological cycle. It describes the exchange of water in every form between the Earth’s systems and is part of what makes the Earth so unique.
Meet the scientists
David Hamilton, Louis Schipper, Dave Campbell and Keith Hunter are New Zealand scientists who each study one aspect of the hydrological cycle. In their studies, they need to consider the Earth as a whole, dynamic9 and interacting system.
Take up the challenge
The Hub has a number of activities that model aspects of the water cycle10.
- Building a water cycle models evaporation and precipitation11.
- Water cycle models use plastic12 bags hung in a sunny window.
- Water run-off models how rain can affect soil erosion13 and ground stability.
- Constructing an aquifer model explores the link between precipitation, surface and ground water.
- Groundwater contamination models how contaminants enter aquifer14 systems.
- Follow the water droplet takes a literary approach to the water cycle.
Other teaching resources include:
- Precipitation and cloud formation is a slide show explaining cloud and precipitation processes.
- What is the Earth system? is a teacher resource that explains the concept of systems.
- Tie it all together with a unit plan featuring resources in Water on the go or use the interactive Learning about the water cycle.
Question bank
The H₂O on the go, the water cycle – question bank provides an initial list of questions the water cycle and places where their answers can be found. The questions support an inquiry approach.
Key terms
For explanations of key concepts, see H2O on the go – key terms.
Timeline
Explore the timeline to look at events in our water cycle from millions of years ago to the present.
Related content
Observing water introduces our Material World resources for NZ Curriculum levels 1 and 2 that explore the characteristics of solids, liquids, gases15 and bubbles by observing water and its unusual properties.
- property: A physical or chemical property is a physical or chemical state of a substance that can be measured. Any changes can be used to describe transformations between states.
- groundwater: Water located beneath the Earth’s surface in soil spaces and in fractures of rocks.
- water vapour: The gas phase of water.
- solar radiation: Radiant energy emitted by the Sun as a result of nuclear fusion reactions.
- heat energy (heat): Heat energy: the transfer of energy in materials from the random movement of the particles in that material. The greater the random movement of particles the more heat energy the material has. Temperature is a measure of the heat energy of a material.
Heat: the flow of energy from a warm object to a cooler object. - molecule: Two or more atoms bonded together. The molecule of an element has all its atoms the same. The molecule of a compound has two or more different atoms.
- molecule: Two or more atoms bonded together. The molecule of an element has all its atoms the same. The molecule of a compound has two or more different atoms.
- evaporation: The process by which a liquid is converted into a gas, without necessarily reaching the boiling point.
- dynamic: In science, a process or system characterised by constant change.
- water cycle: The continuous movement of water on, above and below the surface of the Earth (also known as the hydrological cycle).
- precipitation: 1. The formation of an insoluble solid (precipitate) from a given solution by altering either its temperature, concentration or chemical composition. 2. In meteorology, this term describes the formation of rain, hail, snow or ice in the atmosphere.
- plastic: A synthetic material made from a wide range of organic polymers (such as polyethylene, PVC and nylon) that can be moulded into shape while soft and then set into a rigid or slightly elastic form.
- erosion: Wearing away of the land by mechanical action, such as by wind, water and glaciers, and by material carried in them. It can also be the gradual wearing away of a surface due to friction, particle collisions or chemical attack. Part of the process of erosion transports material away.
- aquifer: A layer of permeable rock or sand that contains water. An aquifer may be freshwater or saline (containing saltwater).
- gases: The state of matter distinguished from the solid and liquid states. Gases have the ability to diffuse readily and to become distributed uniformly throughout any container.
