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[Music]

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water is all around us and it's

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important to nearly every natural

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process on earth cannot be

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underestimated it is the only compound

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that can be found naturally as a liquid

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gas and solid the process by which water

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moves around the earth from the oceans

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to the atmosphere to the land and back

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to the ocean is called the water cycle

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water regulates climate storing heat

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during the day and releasing it at night

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and carries heat from the tropics to the

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poles by sea and by air let's follow a

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single molecule of water beginning in

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the ocean through the paths that might

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take before eventually winding up right

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where it started back in the big blue

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sea the fuel for this journey will be

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provided by our planet's prime energy

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during the day the Sun heats up the air

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and ocean surface causing water

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molecules to evaporate evaporation

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occurs when a liquid molecule of water

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escapes into the air as a gas this

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scientific visualization shows how water

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evaporation indicated in turquoise is

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driven by the energy of the Sun notice

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how the rate of evaporation pulses over

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land it speeds up in the day and almost

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disappears at night over the ocean

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evaporation appears to remain constant

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water in the air in gas form is known as

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water vapor the molecule is now fresh

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water having left the ocean salt and

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other particles behind the water

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evaporates and goes into the atmosphere

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and then it doesn't necessarily just

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turn around and fall as rain or snow

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[Music]

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condensation is the process by which

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water vapor molecules cool stick

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together and become liquid again in

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cloud formation this often happens high

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in the atmosphere where the temperature

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is much lower than it is near the

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surface what happens in the atmosphere

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is just like we have currents in the

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ocean we have winds in the atmosphere

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that actually to some extent Drive what

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goes on in the ocean currents materials

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in the atmosphere can travel actually a

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great distance sometimes you know a

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quarter of a way around the world just

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until they get to the point where they

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actually turn into rain or snow and

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thereby fall back to the ocean or or

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fall back to the land this is called

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precipitation if the water molecule

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falls on land as snow it may be stored

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for a very long period of time in a

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polar ice sheet or mountain glacier

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depending on climate conditions when

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rain falls or the snow melts typically

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the next place it goes it infiltrates

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into the soil so so soil is not a solid

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it's not like a rock there there are

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poor spaces in there and those can be

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filled with water and typically there is

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a certain amount of water in that soil

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at all times if the soil is completely

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if soil becomes saturated any additional

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rainfall will collect in puddles and

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streams soil water that percolates deep

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enough will help to recharge an aquifer

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an aquifer is any underground geologic

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formation that stores water so it's

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typically either rock with a lot of

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cracks in it or it's sandy layer sand

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has a lot of pore space in it it can

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store a lot of water

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the water molecule might remain in an

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aquifer for more than a million years

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more likely it would help to replenish a

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stream which would feed into lakes and

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rivers eventually the water molecule

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will return to where it started the

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ocean people also have a role in the

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water cycle by pumping water out of the

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ground for irrigation cutting down

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forests for development and building

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roads and other concrete surfaces that

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lead to runoff people can have a serious

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impact on the path a water molecule

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takes the most obvious way that people

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affect the water cycle are the ways that

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that we control the water after it's

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fallen on the land surface as rain or

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melts as snow but we have put in dams

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and rivers to to hold this water we also

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put the groundwater out and use that so

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it's these water resources we call them

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are really us taking a natural part of

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the water cycle and using it for

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anything

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the water cycle also affects and is

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affected by climate variations if the

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water cycle is one of the ways that we

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will really feel any changes in climate

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so climate changes will feed back to

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what our cycle changes things like how

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much precipitation and area receives the

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frequency of droughts and floods and

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this sort of thing

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the water cycle is the adventurous

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journey that water takes through the

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oceans atmosphere and land driven by the

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Sun

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improving our understanding of the water

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cycle and how it is changing will be

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critical for future decisions related to