The Water Cycle

75% of Earth’s surface is covered with ocean. 25% of the surface is land (7 continents).

Maybe that’s why Earth is called the Water Planet. The atmosphere over all Earth also contains water in the form of vapour. But there are two kinds of water:

Salt water is in the oceans

Fresh water is everywhere else

Most (97%) of the water on Earth is salt water in the oceans. Earth’s water Only about 3% of Earth’s water is fresh water. Salt water in the oceans 97% Fresh water 3%

There are may types of plants and animals that live in the salt water oceans.

But all the plants and animals that don’t live in the ocean must have fresh (not salt) water to live and grow.

Salt water from the oceans becomes fresh water in a process we call the… Water Cycle.

The water cycle begins when energy from the sun heats ocean water. This heat energy causes evaporation.

evaporation -when liquid water becomes vapor

Evaporation is what happens when water “dries up.”

Water from the oceans is constantly evaporating Water from the oceans is constantly evaporating. Sunlight makes water evaporate faster.

When water evaporates, molecules of water become vapour and float up into the air. Only pure water can evaporate. The salt stays behind in the ocean. s s s s s s

Some vapour gets into the air as it is released from plants Some vapour gets into the air as it is released from plants. This is called transpiration.

Water vapour is not visible in the atmosphere until it cools and condenses into clouds.

condensation - when vapor becomes liquid water

Condensation is the next part of the water cycle where vapor cools and forms clumps of liquid water.

Warm air can hold a lot of vapor but when air cools the vapor condenses into bigger and bigger droplets.

Vapor condenses more and more as it gets cooler Vapor condenses more and more as it gets cooler. Droplets get bigger and clouds get darker.

When the droplets get too heavy they fall to the ground as liquid or frozen water. This step in the water cycle is called precipitation.

precipitation - any water that falls from the sky (rain, snow, sleet, hail)

Precipitation is how the land areas get fresh water that plants and animals need to live.

Some of the precipitation falls as snow Some of the precipitation falls as snow. It may lay on the ground all winter then melt slowly to keep rivers running all summer.

Some precipitation falls as snow and does not melt for many years Some precipitation falls as snow and does not melt for many years. Most of Earth’s fresh water is stored in glaciers.

Some precipitation seeps down underground to form aquifers Some precipitation seeps down underground to form aquifers. We can drill wells to get this fresh water. aquifer

Some precipitation collects in lakes, and ponds Some precipitation collects in lakes, and ponds. Even if water is green, we call it fresh water. Fresh doesn’t mean clean, it means not salty.

A lot of the precipitation runs off into streams and rivers where it flows back to the ocean. This is called runoff.

runoff Precipitation that doesn’t soak into the ground and “runs off” the land to get back to the oceans.

Eventually, all fresh water gets back to the ocean where the cycle of evaporation, condensation, precipitation and runoff can go on and on to supply fresh water to our planet.

A cycle is a wheel that is constantly turning Earth’s water is in a constant cycle. It evaporates from the ocean, travels through the air, rains down on the land and then flows back to the ocean.

Evaporation speeds up when water is heated.

Earth’s atmosphere is warmer near the equator where the Sun’s ray are more direct. The north and south polar regions are colder. cold warm hot warm cold

This is why the areas around the equator where the world is hotter have more rain and humidity.

Some parts of the world seem to be very dry, but even in the desert, there is water. Every living plant and animal contains water and there is water vapor in the air.

For millions of years, some of the rain water that falls has been soaking deep underground. You can find water in these aquifers almost anyplace you drill.

Name 3 kinds of fresh water

Vapour vay pohr Water that is in the gas state. Water molecules that have been evaporated. Vapour is usually invisible but hot steam can be seen for a few seconds before it disappears.

Dew (doo) Small droplets of water that appear on the ground in early morning. Dew can occur even with no clouds when humid air cools at night. Many small animals get the water they need from dew drops.

Convection current Air movements caused by uneven heating of the Earth and temperature differences. Hot air rises, colder air sinks. The result is wind.

Aquifer (ah kwih fur) Big areas of underground water that can be found by drilling almost anyplace on Earth. This is also called the water table.

Drought (rhymes with out) An usually dry period with less than normal amounts of rainfall.

Flood (flahd) An usually wet period with more than normal amounts of rainfall when rivers can’t carry the runoff.

H2O H2 (2 hydrogen atoms) + O (1 oxygen atom) water The chemical formula for water. H2 (2 hydrogen atoms) + O (1 oxygen atom) water ( 1 water molecule)

Frozen H2O = ice Liquid H2O = water Gas H2O = vapor