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You are speeding around the Sun
at 67,000 miles an hour.
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In the next year, you will travel 584 million miles
to end up exactly where you started.
3
00:00:23,896 --> 00:00:29,167
It's a journey the Earth has made more than
four billion times since its formation.
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00:00:32,638 --> 00:00:38,143
As it orbits, our planet also spins,
and is tilted over to the side.
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These three things, orbit, tilt and spin,
have created and shaped our world.
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00:00:56,128 --> 00:01:02,401
In this programme we'll see how spin plays
a key role in controlling the planet we live on.
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It gives us our day and night cycle.
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It drives our most dramatic weather
and controls our climate.
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And has even steered the course of human history.
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00:01:23,689 --> 00:01:27,092
Spin has created the world we know today.
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Every clay and at almost every location on our planet,
nature puts on one of her most majestic displays.
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But we usually ignore it.
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The rise of the sun.
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The vast burning ball that tracks across
our skies used to be considered a god.
15
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But today we take it for granted.
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It's a beautiful sight but it also reminds us of
something it's all too easy to forget.
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00:02:33,291 --> 00:02:38,563
The Earth is spinning as it flies though space,
and we're spinning with it.
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Every day our planet spins once about its axis.
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This is what makes the sun rise and set.
20
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This daily cycle of light and dark
dominates life on Earth.
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With day comes warmth and light.
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Plants use the daytime to grow, converting the light
into energy through photosynthesis.
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And reptiles warm their cold blood in the sun.
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As day turns to night,
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sea creatures of all kinds rise from the depths
into the shallower waters.
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In the darkness they can feed and avoid predators,
retreating again as the sun rises.
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It's the largest migration in the world,
and it happens every day.
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And the blackness of night
also brings with it creatures...
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...that have evolved to live without the sun's light.
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Some have developed huge eyes
to spot prey in the dark,
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while others navigate the darkness using,
not sight, but sound.
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Spin sets the rhythm of life on our planet.
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00:04:12,124 --> 00:04:15,360
But does far more than give us
the cycle of night and day.
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The power of spin actually shapes
the world around us,
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because our rotating Earth creates an effect
that can stir the atmosphere and move the oceans.
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You can really see the spin of the Earth
at work in late August.
37
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In the northern hemisphere,
summer is coming to an end.
38
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But it has a sting in its tail.
39
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Hurricanes, cyclones , typhoons.
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Around the world, these giant rotating storms...
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...can cause billions of dollars of damage
and claim thousands of lives.
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And they only exist because our planet spins.
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Josh Wurman is an atmospheric scientist.
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He's investigating the formation of
these gigantic storms.
45
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A hurricane is a huge rotating column of air,
hundreds of kilometres across,
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that roars across the tropical oceans...
47
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...and occasionally makes landfall
on populated areas,
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causing some of the most destructive weather
that we have on the planet.
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It's the afternoon of the 20th of August 2011.
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Hurricane forecasters are keeping an eye on an area
of low pressure making its way across the Atlantic.
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The spin of the Earth would soon
turn this low pressure system...
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...into one of the most talked-about
weather events in recent history.
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Her name: Irene.
54
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Irene, like many hurricanes,
formed in the eastern and central Atlantic,
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and was forecast to be very strong, very violent,
perhaps a category three hurricane.
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In Florida, MikeTheiss was also watching
lrene's growth very closely.
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Not to avoid her path, but to put himself right in it.
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He's a storm chaser.
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I put myself in a hurricane
where the worst winds are going to be.
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I want people to look at one of my videos
and just be completely awe-inspired...
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...and say like,
'how did that guy survive to - to get that video?'
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There we are, it's crazy.
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The violent hurricane winds Mike puts himself in
are created by the Earth's spin.
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Because the Earth's rotation can twist surface winds
into these huge spiralling storms.
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But before Irene could become a hurricane,
she needed to grow.
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Fortunately for her,
she was born at the right time.
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Throughout the late summer and early fall
the ocean has absorbed a lot of sun, all summer.
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And the ocean has heated up.
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It's about 3O degrees Celsius out there...
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...and that's a huge amount of energy
for thunderstorm clusters to develop...
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...and eventually turn
into tropical storms and hurricanes.
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Heat rises, the warm ocean heats
the moist air above it, forcing it upwards.
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At the ocean's surface, more air rushes in
to replace it, and it too is heated and rises.
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A powerful cycle is set in motion,
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with more and more air being sucked in
towards the low pressure centre.
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00:08:09,094 --> 00:08:15,767
But to become a hurricane, it needs to rotate,
and for that we need one more vital ingredient.
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The spin of the earth.
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Even though we can't feel it,
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our spinning world creates an effect
that has a global impact.
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Strange things happen when you spin.
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We're used to objects travelling
though the air in a straight line.
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But start to rotate, and it's a very different story.
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00:08:52,404 --> 00:08:54,339
No matter where they throw the ball from,
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and no matter who they throw it to,
the ball follows a curved path.
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00:09:01,112 --> 00:09:03,348
And because they're spinning counter-clockwise,
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to the left, from the point of view of the thrower
it's always curved to the right.
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This cun/ing of objects caused by rotation
is called the Coriolis effect.
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00:09:19,264 --> 00:09:22,767
And it's the Coriolis effect
that makes hurricanes spin.
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Because here on Earth
we're spinning like the merry-go-round.
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So just as the balls curve,
the winds on our rotating planet curve too.
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There's very low pressure
at the centre of a hurricane.
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And it's surrounded by higher pressure.
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And normally air would approach that low directly
from the high pressure surrounding it.
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But the Coriolis effect causes that
air to be deflected towards the right,
95
00:09:54,866 --> 00:09:58,236
so the air coming in from all directions
is reflected towards the right...
96
00:09:58,603 --> 00:10:02,941
...and it spirals around the low
instead of going directly in.
97
00:10:03,374 --> 00:10:08,680
And that causes there to be a strong rotation,
a strong spiralling of air, around the hurricane.
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The deeper then that the low is, the more violently
the wind spins around that hurricane.
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By late August,
the Coriolis effect had created a monster.
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Irene was now a powerful hurricane,
and was right on top of the Bahamas.
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And Mike Theiss was there to film it all.
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Here we are in Nassau,
Bahamas on Paradise Island.
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Hurricane Irene has made her presence felt.
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The devastating winds Mike witnessed
were the Earth's spin in action.
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As you see behind me, the trees are whipping
really good in the wind here. Ow!
106
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Just look at that sea.
107
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That says hurricane, right there.
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00:11:03,134 --> 00:11:05,136
Whoa. Wow.
109
00:11:07,138 --> 00:11:08,907
But there was more still to come,
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because as Irene moved on from the Bahamas
she was headed straight for the east coast of the US.
111
00:11:17,282 --> 00:11:22,287
Houston, this storm is now stretching
from Cuba to the Carolinas,
112
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and that is one scary big storm.
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If you are in the projected path of this hurricane,
you have to take precautions now.
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Don't wait, don't delay.
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Irene tracked up towards New York.
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There was wide-scale flooding.
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And the city's transport systems shut down.
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In all, Irene was responsible for
up to seven billion dollars worth of damage...
119
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...and claimed at least 49 lives.
120
00:12:04,329 --> 00:12:07,832
And all of this because our planet spins.
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Hurricanes are dramatic examples of
the Coriolis effect in action.
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00:12:18,876 --> 00:12:21,846
But it impacts on many more areas of our lives.
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Today's planes travel far enough and fast enough
that they need to compensate for the Coriolis effect...
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...to avoid their routes curving off course.
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00:12:36,628 --> 00:12:41,799
If you're thinking of firing a long range missile
and you don't factor in the Coriolis effect,
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you may end up bombing somewhere many miles
from your intended target.
127
00:12:50,508 --> 00:12:55,513
However, one thing it does not do
is affect your bathroom sink.
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The popular myth that household water spirals
in the opposite direction in different hemispheres...
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...is simply not true.
130
00:13:05,056 --> 00:13:09,027
The domestic sink is nowhere near
big enough for it to be a factor.
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00:13:13,464 --> 00:13:21,005
But even if it has no effect on our drains,
the Coriolis effect has a huge impact on life on Earth.
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Because it doesn't just give us hurricanes.
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The curving air the Coriolis effect
creates actually controls our global climate.
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To understand how it does this,
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we need to look closer at the place
where spin has its greatest impact.
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In a field a few miles south of San Francisco,
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a group of engineers are preparing to make
a journey 100,000 feet up into the sky.
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00:14:08,986 --> 00:14:13,057
This isn't NASA,
but with a few hundred dollars worth of equipment,
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they're about to go on a voyage
that normally only astronauts can take.
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00:14:18,796 --> 00:14:21,332
With them is Dr Helen Czerski.
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What we have here is a helium balloon,
and it's going to float up through the atmosphere...
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...and it will give us a really good insight
into all this stuff above our heads.
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Balloons are a fabulous way to look
at the atmosphere,
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because they can look at parts of the atmosphere
that it would be very difficult for a human to look at.
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Attached to the balloon is a GPS transmitter,
to track its journey.
146
00:14:51,062 --> 00:14:54,432
And four cameras will record
everything the balloon sees.
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Its journey will reveal something
you might not expect.
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The movement of the atmosphere is not nearly
as random as you might think.
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Here we go.
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So our balloon has just disappeared
up into the atmosphere.
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I can still see a tiny little white clot.
152
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And now we're going to track it, using GPS
and follow it on its journey through the sky.
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To begin with, the balloon goes
pretty well straight up.
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This is what you'd expect,
because the atmosphere spins with the planet.
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But then the balloon starts to move sideways.
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With the team chasing it,
the balloon is being carried away.
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And this tells us a crucial fact
about the atmosphere:
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Although it spins with the Eart, the atmosphere
isn't completely locked to the surface.
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Okay, it looks like it's just crossing
the freeway at Morgan Hill to the east.
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00:16:23,321 --> 00:16:26,057
While the surface of the Earth is spinning steadily,
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the atmosphere is free to move in
different directions, and at different speeds.
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This free movement of air around the planet...
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...is why the Coriolis effect has such
a big impact on the atmosphere.
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We don't feel the spin because we're too small
and we're attached to the ground, effectively.
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But the atmosphere,
because it's fluid and moving around the planet,
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does feel the influence of the Earth's spin.
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The team is travelling at about 5O miles an hour,
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yet the balloon is continuing to race ahead of them,
blown by the consistently moving air.
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The atmosphere is actually
full of these regular winds,
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constantly moving air around the planet.
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What's passing over the top might seem quite
disordered, quite complex, there's no pattern to it.
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But if you look on a bigger scale,
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there are patterns in the weather
that's passing over each part of the planet.
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00:17:39,664 --> 00:17:43,634
The balloon has now travelled over 8O miles
from its starting point...
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00:17:45,069 --> 00:17:50,741
...and it's about15 miles above the earth's surface,
twice as high as airliners fly.
176
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But it can't go much higher.
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I think the balloon right now
is up near the top of its trajectory,
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so it's about 80,000 feet
above the surface of the Earth.
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00:18:04,088 --> 00:18:08,125
And up where it is there's very little,
very, very low air pressure.
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So about 95 per cent of the atmosphere
is below where this balloon is,
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and because the pressure's so low,
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the balloon will have expanded to
about three times its initial diameter.
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But that is about as much as it can take.
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00:18:36,587 --> 00:18:38,589
As it falls back through the atmosphere,
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the burst balloon is reaching speeds of
around 140 miles an hour.
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Its journey ends in a field
100 miles from its starting point.
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That's just shredded balloon, that's amazing.
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Look at that.
189
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That's just a fantastic picture.
190
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We can see the Earth
and we can see black outer space outside it.
191
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And in between the two there's this fuzzy blue line
which is the atmosphere.
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On this massive planet, only a really thin layer
right at the top is this fluid,
193
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but this dominates our lives.
194
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Fantastic.
195
00:19:44,021 --> 00:19:48,759
The thin layer of air around our planet
may look random and chaotic,
196
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but it's actually highly structured,
large scale consistent winds blow within it.
197
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These winds are all steered by the Coriolis effect,
198
00:20:00,604 --> 00:20:05,743
and this ordering of the atmosphere
has a huge impact on the land below.
199
00:20:13,617 --> 00:20:17,421
When you look at the Earth,
you can see some fairly obvious bands.
200
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White snow at the poles, yellow deserts
and bands of green vegetation in between.
201
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Each reflects dramatically different climate zones,
and each has its own weather.
202
00:20:34,839 --> 00:20:37,575
This division of the Earth into distinctive bands...
203
00:20:37,942 --> 00:20:42,780
...is actually a product of the Coriolis effect
acting on our moving atmosphere.
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00:20:54,692 --> 00:20:58,195
To see how the Earth's spin
can create these climate bands,
205
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we need to go to the place where
this global movement of the atmosphere begins.
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This is the Equator Monument in Ecuador,
and we're here on a particularly significant day.
207
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It's the 23rd of September, the equinox.
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Today at midday,
the sun passes directly overhead here.
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It's the perfect day to show why the equatorial zone
is so important to our global climate system.
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The equinox happens
because the Earth spins at an angle.
211
00:21:51,048 --> 00:21:52,817
It is tilted over to the side.
212
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This means, over a year,
first the northern hemisphere,
213
00:21:58,055 --> 00:22:00,424
then the southern,
points towards the Sun.
214
00:22:03,961 --> 00:22:08,766
The midday sun appears to travel back and forth
across the surface of our planet,
215
00:22:09,266 --> 00:22:14,805
and twice a year, at the equinoxes,
the Sun is directly overhead at the equator.
216
00:22:18,008 --> 00:22:19,610
This means the equator,
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being at the midpoint of the Sun's path,
received more heat than anywhere else.
218
00:22:25,316 --> 00:22:27,818
This has a profound effect on our planet.
219
00:22:31,255 --> 00:22:35,726
With the help of the Earth's spin,
it creates a global system of winds.
220
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These winds will go on to dictate
climate around the world.
221
00:22:48,739 --> 00:22:52,576
The first impact of
this vast movement of air is easy to find.
222
00:22:55,646 --> 00:22:59,283
We're still on the equator,
but we're in the heart of the jungle.
223
00:22:59,650 --> 00:23:01,552
This is the Amazon rainforest.
224
00:23:03,921 --> 00:23:09,226
Sean McCracken is investigating
how the atmosphere creates the vast rainforest.
225
00:23:10,527 --> 00:23:14,765
The answer to that will show us
not just why it's so lush here,
226
00:23:14,999 --> 00:23:19,270
but also why this is the birthplace of
our global climate system.
227
00:23:19,837 --> 00:23:23,874
And it's all down to
the rainforest's location beneath our sun.
228
00:23:25,476 --> 00:23:30,014
The sun here at the equator is just
travelling directly over the top of us.
229
00:23:30,247 --> 00:23:35,552
It really drives all the energy that
these vast number of plants and trees...
230
00:23:35,819 --> 00:23:37,621
...need that we're surrounded by here.
231
00:23:50,401 --> 00:23:56,040
To really see how the atmosphere creates
the rainforest, you need to leave the forest floor.
232
00:23:59,643 --> 00:24:02,680
Rainforests are actually quite surprising places.
233
00:24:04,581 --> 00:24:10,321
With so much heat concentrated on this area,
you might not expect it to be so wet and lush.
234
00:24:12,222 --> 00:24:14,625
But far from drying the rainforest out,
235
00:24:15,025 --> 00:24:20,597
the sun is creating a regular movement of air
that actually feeds the jungle with moisture.
236
00:24:22,066 --> 00:24:25,269
The sun is constantly feeding down
on the equator.
237
00:24:25,502 --> 00:24:31,875
Heat causes the air to rise, as the air rises
from the equator it takes water vapour with it.
238
00:24:34,511 --> 00:24:38,215
Hot moist air is forced to rise by the sun's heat.
239
00:24:38,649 --> 00:24:41,218
This is the start of our planetary wind system.
240
00:24:43,620 --> 00:24:46,957
And it is also the key
to the rainforest climate zone.
241
00:24:49,760 --> 00:24:52,930
As it rises, it condenses, it cools down.
242
00:24:53,530 --> 00:25:01,905
As it cools, those water droplets coalesce into
large rain droplets returning to the forest as rain.
243
00:25:05,542 --> 00:25:10,080
The jungle here can receive
over a hundred inches of rain every year.
244
00:25:11,749 --> 00:25:16,620
The high volume of water
that drops here in the form of rain...
245
00:25:17,054 --> 00:25:21,325
...really is what drives
the high biodiversity that we find here,
246
00:25:21,525 --> 00:25:28,399
creating these vast stretches of rainforest within
a small area around the equator on the planet.
247
00:25:31,568 --> 00:25:33,470
But this is not the end of the story.
248
00:25:34,538 --> 00:25:39,209
Because the rising air that created the rainforest
doesn't stay at the equator.
249
00:25:40,978 --> 00:25:46,617
With the Earth's spin, it's about to create yet
another huge climate band around the Earth.
250
00:25:49,820 --> 00:25:54,792
The air rises high into the atmosphere,
to around 1O miles up.
251
00:25:56,493 --> 00:25:58,429
It has nowhere to go but out,
252
00:25:58,662 --> 00:26:03,067
and spreads north and south,
drawn towards the cooler poles.
253
00:26:05,536 --> 00:26:09,373
But thanks to the Coriolis effect,
it follows a curved path.
254
00:26:11,075 --> 00:26:13,877
In the northern hemisphere bending to the right.
255
00:26:16,480 --> 00:26:20,918
This huge river in the sky
is now circling from west to east.
256
00:26:28,892 --> 00:26:34,131
Dr Czerski is on her way to meet that air
as it changes direction once again.
257
00:26:39,403 --> 00:26:42,573
As the air travels northwards
it gets bent to the right,
258
00:26:42,673 --> 00:26:46,643
and as it's bent around to the right
it starts to - to cool down,
259
00:26:46,877 --> 00:26:49,213
to become more dense, and to sink.
260
00:26:52,749 --> 00:26:55,853
And l'm going to join that
airstream by going out of this door.
261
00:27:04,161 --> 00:27:05,329
Okay, here we go.
262
00:27:10,901 --> 00:27:13,570
The air that left the equator has now cooled.
263
00:27:13,971 --> 00:27:17,908
And just as the hot air rises,
so too cold air descends,
264
00:27:18,208 --> 00:27:20,777
dramatically changing the landscape below.
265
00:27:23,013 --> 00:27:28,285
Dr Czerski is now 10,000 feet above Arizona,
travelling with that air.
266
00:27:35,592 --> 00:27:40,297
So we're falling now together,
along with all that air, this waterfall of sky.
267
00:27:57,447 --> 00:27:59,082
Ah, glad to be back on the ground.
268
00:27:59,883 --> 00:28:05,822
So l've landed in a really dry, dusty place with just
these scrubby little bushes around.
269
00:28:08,458 --> 00:28:11,195
This is the Sonoran Desert in North America.
270
00:28:11,628 --> 00:28:14,164
It's two thousand miles north of the equator.
271
00:28:18,502 --> 00:28:21,538
In the summer,
it can reach 5O degrees centigrade.
272
00:28:22,105 --> 00:28:24,675
But it's not heat that defines a desert.
273
00:28:24,775 --> 00:28:26,043
It's the lack of water.
274
00:28:32,149 --> 00:28:35,886
Here it can rain as little as three inches in a year,
275
00:28:35,986 --> 00:28:40,023
so it's no surprise that the wildlife
is very different from the rainforest.
276
00:28:41,291 --> 00:28:43,660
This is a classic dry environment.
277
00:28:43,760 --> 00:28:45,028
You can see there's no water here.
278
00:28:45,262 --> 00:28:49,433
Stones, sand on the ground,
and the plants - look at this:
279
00:28:49,700 --> 00:28:54,104
spiky, very unfriendly plant
holding onto the moisture it's got.
280
00:28:56,406 --> 00:29:00,477
The Coriolis effect caused the equatorial air
to descend here.
281
00:29:01,245 --> 00:29:06,917
It's still the same air that created the lush rainforest,
so why is now so dry?
282
00:29:07,818 --> 00:29:12,022
So when that air rose at the equator,
it took lots and lots of moisture with it.
283
00:29:12,222 --> 00:29:16,193
But as it rose up, all of that moisture
rained out back down into the tropics.
284
00:29:16,460 --> 00:29:20,097
And so as it started its journey away
from the tropics towards us here,
285
00:29:20,297 --> 00:29:21,832
it was very, very dry air.
286
00:29:24,334 --> 00:29:27,004
By bending the dry equatorial air,
287
00:29:27,304 --> 00:29:32,476
the spin of the Earth has created a desert
two thousand miles north of the equator.
288
00:29:33,877 --> 00:29:36,246
And it doesn'tjust happen in North America.
289
00:29:38,482 --> 00:29:41,385
All around the planet,
where that dry air is descending,
290
00:29:41,585 --> 00:29:44,187
you get deserts,
both north and south of the equator;
291
00:29:44,288 --> 00:29:46,923
there are two bands of deserts
going all the way around the planet.
292
00:29:51,495 --> 00:29:58,335
There's the Thar Desert in India, the Arabian,
and of course there's the Sahara in Africa.
293
00:29:59,403 --> 00:30:04,474
They're all created by falling dry air
that originated close to the equator.
294
00:30:07,477 --> 00:30:11,648
These deserts form
the second great climate zone round our plant.
295
00:30:12,182 --> 00:30:15,419
If it wasn't for the spin of the Earth,
it wouldn't exist.
296
00:30:22,959 --> 00:30:25,962
But the air that falls in the desert doesn't stay here.
297
00:30:26,363 --> 00:30:28,265
It has one final journey to make.
298
00:30:29,399 --> 00:30:33,403
And arguably for us,
it's been the most important of them all.
299
00:30:34,471 --> 00:30:37,874
The air that's arriving here now will
get sucked back towards the equator,
300
00:30:38,141 --> 00:30:42,913
and as it goes it's bent to the right by
the Coriolis effect, so you get close to the equator,
301
00:30:43,146 --> 00:30:46,683
big winds going round towards the west,
and we call those the trade winds.
302
00:30:49,553 --> 00:30:53,190
The trade winds form a band of consistently
moving westward air,
303
00:30:53,590 --> 00:30:55,492
and from the 15th century onwards,
304
00:30:55,826 --> 00:31:00,697
European sailors increasingly exploited
these winds to explore the world.
305
00:31:04,201 --> 00:31:07,771
They played a central role
in the colonisation of the Americas,
306
00:31:08,171 --> 00:31:11,341
and world exploration during the age of sail.
307
00:31:14,010 --> 00:31:16,847
The trade winds were the freeways of the ocean.
308
00:31:19,516 --> 00:31:22,085
The pattern of our planet,
the rainforest at the equator,
309
00:31:22,386 --> 00:31:25,021
the deserts at about 3O degrees of latitude,
310
00:31:25,288 --> 00:31:27,290
even the course of human history itself,
311
00:31:27,557 --> 00:31:30,694
all those would be completely different
if our planet didn't spin.
312
00:31:33,997 --> 00:31:37,901
When the trade winds arrive back at the equator,
they close the loop.
313
00:31:39,903 --> 00:31:43,774
The resulting pattern of wind is called a circulation cell.
314
00:31:44,274 --> 00:31:46,510
But it doesn't exist in isolation.
315
00:31:48,078 --> 00:31:51,515
The pattern repeats,
covering our entire planet.
316
00:31:54,050 --> 00:31:57,988
With three cells in the northern hemisphere
and three in the southern,
317
00:31:58,288 --> 00:32:01,224
the Earth's spin brings order to the atmosphere,
318
00:32:01,558 --> 00:32:05,462
creating the climate zones
we're so familiar with today.
319
00:32:09,166 --> 00:32:14,604
The atmosphere is not the only place where
the Coriolis effect makes its presence felt.
320
00:32:15,338 --> 00:32:17,340
It can move OCGGHS tOO.
321
00:32:20,577 --> 00:32:23,780
Two thirds of the Earth's surface
is covered with water.
322
00:32:24,080 --> 00:32:28,318
Just like the atmosphere,
it too is free to move around the planet.
323
00:32:32,055 --> 00:32:35,525
This means the Earth's spin
can control the oceans.
324
00:32:37,394 --> 00:32:40,664
And this has a huge impact on the world's climate.
325
00:32:50,674 --> 00:32:53,677
Professor Meric Srokosz is an oceanographer.
326
00:32:54,244 --> 00:32:57,848
He's investigating the movement of water
in the North Atlantic.
327
00:33:00,650 --> 00:33:01,418
So we look at the action.
328
00:33:01,685 --> 00:33:04,387
You can see the surface waves,
and it looks very dynamic,
329
00:33:04,821 --> 00:33:07,924
but underneath the surface
there's lots of dynamic stuff going on as well.
330
00:33:08,825 --> 00:33:10,760
Beneath the waves, there's large scale currents,
331
00:33:10,994 --> 00:33:14,931
and they're moving water round in the ocean
a bit like the winds blowing in the atmosphere.
332
00:33:18,401 --> 00:33:23,139
And just like the winds in the atmosphere,
the Coriolis effect comes into play.
333
00:33:24,674 --> 00:33:27,577
Rotation is important for the ocean,
just like it is for the atmosphere.
334
00:33:28,278 --> 00:33:29,813
Because the planet is rotating,
335
00:33:30,046 --> 00:33:32,148
the rotation causes the currents to veer,
336
00:33:32,482 --> 00:33:36,620
and that has a big effect in terms of the way
the currents flow in the ocean.
337
00:33:39,589 --> 00:33:44,528
Like the winds above,
the Coriolis effect is bending the currents below.
338
00:33:46,029 --> 00:33:49,933
This helps create huge circular currents
in our planet's oceans.
339
00:33:51,935 --> 00:33:58,041
In the northern hemisphere they rotate clockwise,
and in the southern they rotate counter-clockwise.
340
00:34:03,914 --> 00:34:10,220
They're called ocean gyres, and surprisingly,
they play a crucial role in the world's climate.
341
00:34:11,788 --> 00:34:15,091
Because it's not just water
they're moving around the ocean.
342
00:34:15,525 --> 00:34:17,160
They're moving heat too.
343
00:34:23,800 --> 00:34:26,136
L'll give you a shout when the first buoys are over.
344
00:34:28,138 --> 00:34:34,377
Since 2001, Meric and his team have been
gathering data at various sites in the North Atlantic.
345
00:34:37,113 --> 00:34:40,817
Our research in the Atlantic is looking at
the effect of the currents in the Atlantic...
346
00:34:40,917 --> 00:34:42,519
...in terms of bringing heat northwards.
347
00:34:43,053 --> 00:34:47,991
Essentially the sun heats the earth at the equator
more than it does at the pole.
348
00:34:48,792 --> 00:34:51,528
The ocean currents are moving
a large amount of water.
349
00:34:51,761 --> 00:34:56,766
Associated with that water is heat,
and that helps to balance the global climate system.
350
00:35:00,670 --> 00:35:05,976
The currents in our oceans are transporting
vast amounts of energy away from the equator.
351
00:35:08,745 --> 00:35:10,347
In the North Atlantic alone,
352
00:35:10,547 --> 00:35:15,919
the equivalent to one million power stations worth
of energy is being transported northwards.
353
00:35:17,087 --> 00:35:21,157
This energy helps warm temperate zones
far north of the equator.
354
00:35:24,628 --> 00:35:30,667
The ocean gyres are moderating the Earth's climate
and it's our planet's spin that makes them turn.
355
00:35:36,206 --> 00:35:39,909
These vast ocean currents have local effects too.
356
00:35:40,644 --> 00:35:43,513
The current moving north
along the west coast of Chile...
357
00:35:43,880 --> 00:35:47,617
...brings up cold nutrient-rich water
from the depths.
358
00:35:50,020 --> 00:35:53,657
This creates one of the most fertile
fishing grounds on Earth.
359
00:35:53,923 --> 00:35:58,495
2O per cent of the world's fish is caught from
less than one per cent of the ocean.
360
00:36:06,336 --> 00:36:11,708
The heat transported in the North Atlantic gyre
is swept east by the prevailing winds.
361
00:36:14,944 --> 00:36:19,549
This means, even in December you can go
swimming off the coast of the UK.
362
00:36:21,184 --> 00:36:26,322
Whilst at the same latitude in Eastern Canada,
the landscape can be frozen solid.
363
00:36:33,730 --> 00:36:39,135
Far from simply giving us day and night,
the Earth's spin shapes our planet.
364
00:36:39,969 --> 00:36:46,376
Through the Coriolis effect, it orders the atmosphere,
giving us our global climate structure.
365
00:36:47,644 --> 00:36:54,150
And it controls the movement of ocean currents,
transporting the sun's energy around the world.
366
00:36:55,985 --> 00:36:59,656
But the Earth's spin plays
another crucial role in our world.
367
00:37:05,095 --> 00:37:08,832
A role that not only has a huge
daily impact on the planet;
368
00:37:09,165 --> 00:37:12,035
it has dramatically altered the Earth's history.
369
00:37:18,541 --> 00:37:22,312
And the best place to see it in action
is on the Eastern coast of Canada.
370
00:37:24,047 --> 00:37:28,418
Dr Graham Dayborn has come here
to witness one of nature's great events.
371
00:37:31,721 --> 00:37:34,791
Well, we're here in the upper end
of the Bay of Fundy.
372
00:37:35,191 --> 00:37:39,662
It is, as you can see, a spectacular setting.
373
00:37:40,296 --> 00:37:44,934
But the fascination about this is the enormous tide.
374
00:37:47,937 --> 00:37:51,141
The Bay of Fundy has the largest tides in the world.
375
00:37:53,076 --> 00:37:55,178
Every day the water drains away.
376
00:37:58,915 --> 00:38:00,583
This is the sea floor.
377
00:38:02,252 --> 00:38:06,990
And these land masses are actually islands
left behind by the receding tides.
378
00:38:09,626 --> 00:38:13,029
The water has travelled out
three miles from the coastline.
379
00:38:18,835 --> 00:38:22,138
Right now, the tide is coming into the Bay of Fundy.
380
00:38:22,372 --> 00:38:24,240
This is driven in from the Atlantic,
381
00:38:24,507 --> 00:38:29,345
but as it enters the Bay of Fundy
it gets into shallower and shallower water,
382
00:38:29,813 --> 00:38:33,883
and as a result, it is forced to rise higher and higher.
383
00:38:34,651 --> 00:38:39,355
There is about a hundred billion tonnes of water
that come in over six hours.
384
00:38:40,423 --> 00:38:46,362
That is as much as all the water in the rivers
in the world flowing out at the same time.
385
00:38:51,701 --> 00:38:56,873
The bay's unique shape and location
mean the tides here are the biggest in the world.
386
00:39:02,078 --> 00:39:07,851
This huge movement of water only happens because
the Earth doesn't travel around the sun alone.
387
00:39:09,819 --> 00:39:12,589
It has a companion - the moon.
388
00:39:16,860 --> 00:39:22,732
So here we are, having witnessed this enormous
rise of water over the last six hours.
389
00:39:23,299 --> 00:39:26,202
All of that is entirely due to the fact that...
390
00:39:26,436 --> 00:39:31,975
...the moon is attracting that water
and pulling it away from the Earth, if you like.
391
00:39:33,576 --> 00:39:40,083
We experience and see that
as a bulge and a - a flood of water.
392
00:39:45,088 --> 00:39:47,056
But the moon and the tidal bulge...
393
00:39:47,323 --> 00:39:52,262
...it creates are not enough to give us
the daily cycle of tides that we're so familiar with.
394
00:39:54,097 --> 00:39:55,698
We need spin too.
395
00:39:58,534 --> 00:40:03,239
We can almost think of the water as being static
and the Earth spinning underneath it,
396
00:40:03,606 --> 00:40:07,877
and that's why you see the tide coming in,
the tide going out,
397
00:40:08,077 --> 00:40:12,949
but it's really because the Earth itself
has rotated underneath that envelope of water.
398
00:40:15,818 --> 00:40:20,823
The moon is overhead, the Bay of Fundy
is now in the middle of this huge bulge.
399
00:40:22,792 --> 00:40:24,360
Thanks to the Earth's spin,
400
00:40:24,594 --> 00:40:29,332
the rock formations Dr Dayborn walked past
have become islands once again.
401
00:40:31,901 --> 00:40:39,642
In the last six hours, the water in this basin here,
which is, as you can see, very, very large,
402
00:40:40,109 --> 00:40:44,681
has raised about 4O feet, 4O to 45 feet.
403
00:40:44,914 --> 00:40:48,251
If you took a five-storey building and
put it at the low tide mark,
404
00:40:48,518 --> 00:40:50,253
right now you would not be able to see it.
405
00:40:54,290 --> 00:40:59,462
The highest tides happen when the gravity of
the moon works together with the gravity of the sun.
406
00:41:04,600 --> 00:41:07,937
But in late September, something special happens.
407
00:41:10,006 --> 00:41:13,810
Then both the sun and the moon
are tracking along the equator.
408
00:41:15,778 --> 00:41:18,314
As they pass over the centre of our planet,
409
00:41:18,581 --> 00:41:22,385
we spin right through the middle of
a mammoth tidal bulge.
410
00:41:22,952 --> 00:41:24,587
We have our biggest tides.
411
00:41:26,990 --> 00:41:30,393
This leads to strange events happening
around the world.
412
00:41:33,730 --> 00:41:37,433
In certain river valleys,
tidal waves race upstream.
413
00:41:37,967 --> 00:41:39,736
These are tidal bores.
414
00:41:41,537 --> 00:41:43,740
In Britain, there's the river Severn.
415
00:41:48,511 --> 00:41:51,414
In South America there's the Amazon bore.
416
00:41:57,353 --> 00:42:01,190
The biggest of them all
is on the Quiantang river in China.
417
00:42:03,793 --> 00:42:05,561
They call it the Silver Dragon,
418
00:42:05,795 --> 00:42:10,767
and in late September surfers from across
the world head to the city of Hangzhou...
419
00:42:11,000 --> 00:42:14,237
...for one of the more
unusual surfing events of the calendar.
420
00:42:26,682 --> 00:42:29,419
Our tides can be spectacular sights,
421
00:42:29,752 --> 00:42:33,022
but they do much more than move
water around the planet.
422
00:42:37,560 --> 00:42:39,028
Off the coast of Bermuda,
423
00:42:39,395 --> 00:42:44,067
Dr Judith Nagel-Myers is looking for
a particular sort of sea creature.
424
00:42:46,502 --> 00:42:51,974
One that can tell us about the extraordinary role
tides have played in the history of the Earth's spin.
425
00:42:55,078 --> 00:42:56,879
The sea creature is coral.
426
00:42:59,549 --> 00:43:03,453
Corals are little animals that
you can find in the warm seas of the tropics,
427
00:43:03,719 --> 00:43:07,256
and it's amazing that these little animals
can build those colourful,
428
00:43:07,690 --> 00:43:10,760
various shapes and forms on the ocean floor.
429
00:43:25,374 --> 00:43:29,278
But corals do far more than
make the sea floor look pretty.
430
00:43:29,779 --> 00:43:35,318
Encoded within them is a record of
a very significant feature of our planet's rotation.
431
00:43:37,854 --> 00:43:39,889
Corals need a lot of sunlight.
432
00:43:40,089 --> 00:43:42,458
At day they grow very much faster than at night.
433
00:43:42,692 --> 00:43:45,027
So when you look at the skeleton of a coral,
434
00:43:45,294 --> 00:43:49,332
you can see day layers and night layers,
just similar to tree rings.
435
00:43:50,700 --> 00:43:55,104
Every day the coral puts down
a very thin layer of limestone.
436
00:43:55,571 --> 00:44:00,409
This means coral skeletons effectively count
how many days there are in a year.
437
00:44:02,945 --> 00:44:06,616
And this reveals something very strange
about the Earth's past.
438
00:44:09,085 --> 00:44:10,620
This is a modern coral,
439
00:44:10,820 --> 00:44:14,624
which we actually cut so we can see exactly
how those animals grow.
440
00:44:14,857 --> 00:44:17,660
And if you look close you'll see growth bands.
441
00:44:17,760 --> 00:44:19,862
You see dark and bright growth bands.
442
00:44:20,096 --> 00:44:23,032
Those actually represent one year of coral growth.
443
00:44:23,266 --> 00:44:26,769
If you would come even closer
and look under a microscope,
444
00:44:27,003 --> 00:44:32,208
you can see very fine layers
which represent one day of coral growth.
445
00:44:32,441 --> 00:44:38,447
And obviously in modern corals
you can count 365 rings for this one year.
446
00:44:40,249 --> 00:44:43,252
But corals have been around for millions of years,
447
00:44:43,619 --> 00:44:48,057
and when you look at a much older piece of coral,
it tells a very different story.
448
00:44:48,491 --> 00:44:51,627
You can find fossilised corals all over the world.
449
00:44:51,861 --> 00:44:54,897
This is a coral that is 400 million years old.
450
00:44:55,198 --> 00:45:00,236
If you look close you can see the same growth lines
that you can find on a modern coral.
451
00:45:02,605 --> 00:45:09,412
But if you count those daily growth rings,
you don't get 365, as you might expect.
452
00:45:11,247 --> 00:45:16,786
Surprisingly, you find that
there's actually 410 growth rings per year.
453
00:45:17,386 --> 00:45:21,424
That tells us something really interesting
about the Earth's history.
454
00:45:21,691 --> 00:45:27,763
These fossil corals tell us that the Earth spun
much quicker back 400 million years ago.
455
00:45:32,401 --> 00:45:40,643
400 million years ago,
a year lasted not 365 days, but 410.
456
00:45:41,477 --> 00:45:45,881
And the only explanation for this
is that the Earth was spinning faster.
457
00:45:46,449 --> 00:45:51,454
In fact, a day wouldn't have lasted 24 hours,
it would have lasted just 21.
458
00:45:56,792 --> 00:46:01,464
To find out why, you have to go back
to the earliest days of Earth's history.
459
00:46:08,838 --> 00:46:13,843
Four and a half billion years ago,
as the solar system was still forming,
460
00:46:14,176 --> 00:46:19,415
the young Earth was hit by another fledgling planet,
roughly the size of Mars.
461
00:46:31,260 --> 00:46:33,696
Our world only just survived.
462
00:46:39,769 --> 00:46:43,606
Debris from the impact then coalesced
creating the moon,
463
00:46:43,906 --> 00:46:47,209
which would have been much closer
to the Earth than it is today.
464
00:46:49,045 --> 00:46:52,014
It also set the Earth spinning much faster.
465
00:46:54,450 --> 00:46:56,485
When the first oceans formed,
466
00:46:56,719 --> 00:47:03,059
that would have led to tides hundreds of metres high
crashing into the coastlines all around the world.
467
00:47:05,895 --> 00:47:10,066
But the effect of the moon's gravity
pulling on these huge tides,
468
00:47:10,366 --> 00:47:13,169
has actually slowed down the Earth's spin.
469
00:47:14,704 --> 00:47:21,677
The moon creates tidal bulges on our Earth,
and the Earth is trying to spin underneath them,
470
00:47:21,911 --> 00:47:26,248
and that causes friction
that actually slows - slows the rotation down.
471
00:47:30,119 --> 00:47:31,654
Over millions of years,
472
00:47:31,887 --> 00:47:35,424
the tides have actually decreased
the speed of the Earth's spin,
473
00:47:36,192 --> 00:47:40,396
until the days became the 24 hours
we are so familiar with now.
474
00:47:42,998 --> 00:47:47,103
And as our spin has slowed,
so the moon has drifted away,
475
00:47:47,403 --> 00:47:49,205
and its effects have decreased.
476
00:47:51,741 --> 00:47:56,445
But even today, the speed at which
the Earth spins is still slowing down.
477
00:47:56,979 --> 00:48:03,819
Our days are still getting longer,
but only by about 2.3 milliseconds every century.
478
00:48:11,761 --> 00:48:16,232
We've seen how the Earth's spin
plays a critical role in our life on Earth.
479
00:48:17,800 --> 00:48:25,608
Far from just creating our familiar day/night cycle,
it defines weather across the planet.
480
00:48:29,111 --> 00:48:30,913
It creates hurricanes.
481
00:48:32,815 --> 00:48:36,051
It moves oceans and causes the tides.
482
00:48:38,387 --> 00:48:41,590
And spin gives us our deserts and rainforests,
483
00:48:41,991 --> 00:48:45,928
a global pattern of climate zones
that can be seen from space.
484
00:48:49,331 --> 00:48:52,535
But we've also seen how our spin is not constant.
485
00:48:53,836 --> 00:48:57,506
As it has changed,
so too has life on our planet.
486
00:48:59,508 --> 00:49:01,710
The story of spin is not over.
487
00:49:02,311 --> 00:49:07,750
It will continue to shape and reshape our world
for millions of years to come.
49050
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