Transcript presented the water cycle

THIRD POSITION
Topic; Water cycle
The water in your glass may have fallen from the sky as rain just
last week, but the water itself has been around pretty much as
long as the earth has!
When the first fish crawled out of the ocean onto the land, your
glass of water was part of that ocean. When the Brontosaurus
walked through lakes feeding on plants, your glass of water was
part of those lakes. When kings and princesses, knights and
squires took a drink from their wells, your glass of water was part
of those wells.
• Earth's water is
always in movement,
and the water cycle,
also known as the
hydrologic cycle,
describes the
continuous movement
of water on, above,
and below the surface
of the Earth.
•Since the water cycle is truly a "cycle," there is
no beginning or end. Water can change states
among liquid, vapor, and ice at various places in
the water cycle, with these processes happening
in the blink of an eye and over millions of years.
• Although the balance
of water on Earth
remains fairly
constant over time,
individual water
molecules can come
and go in a hurry. The
water in the apple you
ate yesterday may
have fallen as rain
half-way around the
world last year or
could have been used
100 million years ago
by Mama Dinosaur to
give her baby a bath.
• There will never be any more freshwater on Earth than there is
now. No new water is being made and water can’t escape from
the Earth. The water we use is recycled over and over again.
•
• The water cycle is the simplest natural cycle on Earth. Solar
energy evaporates water from the ocean, lakes and rivers.
Millions of litres of water rise into the atmosphere as an invisible
gas - water vapour. This process is called evaporation.
•
• As the water vapour is pushed over the land by winds and rises
over mountains, the water vapour cools and turns back into tiny
water droplets, forming clouds. The droplets joining together is
termed condensation. These droplets fall to earth as rain
(precipitation).
•
• The rain runs into streams and rivers, which eventually flow into
lakes or the sea and the cycle begins all over again.
Millions of years ago there were no oceans on the
planet. The surface of the Earth was so hot that water
simply boiled away. But volcanoes poured huge
amounts of steam into the atmosphere and as the Earth
cooled down the steam turned to water vapor that
condensed as droplets and began to fall as rain. This
downpour lasted for many thousands of years filling
great hollows in the land and thus forming the world's
first seas.
The water cycle is the only way that Earth can be continually
supplied with fresh water. The heat from the sun is the most
important part of renewing our water supply.
This heat soaks up water from the oceans, lakes, rivers, trees
and plants in a process called evaporation.
As the water mixes with the air it forms water vapor. As the
air cools, the water vapor forms clouds. This is called
condensation.
Most of the water is immediately returned to the seas by
rain (precipitation). The rest of the water vapor is carried
inside clouds by wind over land where it rains or snows.
Rain and melted snow is brought back to the oceans by
rivers, streams, and run-off from glaciers and water
underground.
• The water cycle is the way the Earth uses and recycles water.
It's controlled by the sun, which produces energy in the form of
heat. This heat energy causes the water in the world's oceans,
lakes, and even puddles in your backyard to warm and
evaporate. When water is heated, it changes from a liquid to a
gas. This gas is called water vapor, and the process is called
evaporation. When plants give off water vapor, it's called
transpiration. When water evaporates, it rises into the cooler
air, collects, and forms clouds. There, the water vapor
molecules cool down and change back into liquid