How
does the water get into the atmosphere?
Only a tiny fraction of Earth’s water is in the atmosphere at any
one time. It doesn’t stay up there for long and there are several
different ways that it can get up there!
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Heat from the Sun causes water to evaporate from the surface of lakes
and oceans. This turns the liquid water into water vapor in the atmosphere.
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Plants, too, help water get into the atmosphere through a process called
transpiration! After absorbing water from the ground, plants “sweat”
water vapor through their leaves to stay cool.
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Water can also get into the atmosphere from snow and ice. Instead of
melting, some frozen water changes into water vapor gas and goes into
the atmosphere through a process called sublimation.
How
long does water spend in the atmosphere?
On average, water spends about eight days in the atmosphere before it
falls back to Earth. It travels in the wind over oceans and over land.
That sounds like quite an exciting trip!
How
does it get out of the atmosphere?
When the water vapor comes out of the air, it often causes precipitation
like rain and snow. First, when water vapor is cooled it transforms into
tiny droplets of liquid water or ice crystals that grab onto particles
of dust in the atmosphere. Tons of these little droplets or ice crystals
make clouds. When you look at clouds from the ground, the tiny droplets
and ice are too far away to see, but many of them together look like a
cloud. If the droplets or ice crystals get large enough, they fall from
the sky as rain or snow.
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