1
00:00:02,750 --> 00:00:04,618
Our world formed

2
00:00:04,620 --> 00:00:07,854
through a series
of devastating cataclysms...

3
00:00:09,490 --> 00:00:11,791
It could have literally
blown the Earth to bits,

4
00:00:11,793 --> 00:00:13,994
and then we wouldn't even have
a planet today.

5
00:00:13,996 --> 00:00:18,899
...An apocalyptic
planetary collision,

6
00:00:18,901 --> 00:00:22,369
millions
of brutal cosmic strikes,

7
00:00:22,371 --> 00:00:26,373
and the most powerful blast
in the Universe,

8
00:00:26,375 --> 00:00:27,741
a supernova.

9
00:00:27,743 --> 00:00:32,045
Our atoms would have been
scattered into outer space.

10
00:00:32,047 --> 00:00:38,885
Yet, these catastrophes created
the planet we know today.

11
00:00:38,887 --> 00:00:40,854
The Earth is
an incredibly special place.

12
00:00:40,856 --> 00:00:43,356
It seems like everything has
worked out just perfectly.

13
00:00:43,358 --> 00:00:48,762
Could other planets have formed
the same way?

14
00:00:48,764 --> 00:00:53,633
If so, the Universe could be
full of earths...

15
00:00:53,635 --> 00:00:56,069
and full of life.

16
00:00:56,071 --> 00:01:00,071

 How the Universe Works  2x08 

Birth of the Earth Original Air Date on August 29, 2012

17
00:01:00,082 --> 00:01:04,082
== sync, corrected by elderman ==

18
00:01:12,453 --> 00:01:14,521
Our planet is extraordinary.

19
00:01:16,891 --> 00:01:20,260
It provides
everything life needs --

20
00:01:20,262 --> 00:01:25,932
trillions of creatures, plants,

21
00:01:25,934 --> 00:01:29,302
and us.

22
00:01:29,304 --> 00:01:31,771
Well, you look down
at the Earth from space

23
00:01:31,773 --> 00:01:34,374
and everything
that we know of that's life

24
00:01:34,376 --> 00:01:38,278
is down there on that planet,
that beautiful planet

25
00:01:38,280 --> 00:01:42,249
that you now are going around
every hour and a half,

26
00:01:42,251 --> 00:01:44,985
and that's
almost overwhelming --

27
00:01:44,987 --> 00:01:47,787
just the beauty of the Earth.

28
00:01:47,789 --> 00:01:51,691
It's unique in our solar system,

29
00:01:51,693 --> 00:01:55,962
but is it unique
in the Universe?

30
00:01:55,964 --> 00:01:57,330
It's important
for us to understand

31
00:01:57,332 --> 00:02:00,567
the conditions that led
to the formation of the Earth

32
00:02:00,569 --> 00:02:01,901
because then we can
look for those conditions

33
00:02:01,903 --> 00:02:03,570
around other stars.

34
00:02:03,572 --> 00:02:05,572
And if we find
those conditions there,

35
00:02:05,574 --> 00:02:06,740
then that would suggest

36
00:02:06,742 --> 00:02:08,575
that other earths could be
forming

37
00:02:08,577 --> 00:02:09,876
elsewhere in the Universe.

38
00:02:13,114 --> 00:02:16,950
Could there be other planets
like ours among the stars?

39
00:02:19,920 --> 00:02:24,057
To find out,
we must travel back in time...

40
00:02:26,060 --> 00:02:29,663
...and discover
how the Earth was made.

41
00:02:35,936 --> 00:02:40,340
Rewind the clock
4 1/2 billion years,

42
00:02:40,342 --> 00:02:42,309
and this is what you see.

43
00:02:44,512 --> 00:02:50,583
This speck of dust will
become the Earth

44
00:02:50,585 --> 00:02:54,554
by combining
with countless others.

45
00:02:54,556 --> 00:02:57,891
They're all part
of a giant cloud

46
00:02:57,893 --> 00:03:00,994
called a stellar nursery.

47
00:03:00,996 --> 00:03:03,563
The first step
of planetary formation

48
00:03:03,565 --> 00:03:06,599
is about to start...

49
00:03:11,539 --> 00:03:14,974
...an event that will
transform the cloud

50
00:03:14,976 --> 00:03:20,513
into thousands
of infant solar systems,

51
00:03:20,515 --> 00:03:22,716
including our own.

52
00:03:28,656 --> 00:03:31,391
The same process
is happening today,

53
00:03:31,393 --> 00:03:36,629
7,000 light-years away,
in the Eagle Nebula.

54
00:03:39,233 --> 00:03:42,235
Our own solar system formed

55
00:03:42,237 --> 00:03:48,308
inside clouds of gas and dust
like these.

56
00:03:48,310 --> 00:03:52,112
There are
these three trunks of gas,

57
00:03:52,114 --> 00:03:54,314
and they're nicknamed
the "pillars of creation,"

58
00:03:54,316 --> 00:03:56,483
and they're
trillions of miles long.

59
00:03:56,485 --> 00:03:57,851
These are huge structures.

60
00:03:57,853 --> 00:04:01,154
The clouds look dense,

61
00:04:01,156 --> 00:04:04,924
but they're
actually very sparse.

62
00:04:04,926 --> 00:04:07,227
These gas clouds are
incredibly tenuous.

63
00:04:07,229 --> 00:04:08,528
You'd have to compress,

64
00:04:08,530 --> 00:04:12,599
basically, a mountain's volume
worth of this stuff,

65
00:04:12,601 --> 00:04:15,602
squeeze it down just to make
a little, tiny rock like this.

66
00:04:15,604 --> 00:04:23,076
To compress the gas and dust
into dense stars and planets

67
00:04:23,078 --> 00:04:27,947
takes
a supremely powerful event --

68
00:04:27,949 --> 00:04:33,253
one that can only follow
the death of a giant star.

69
00:04:33,255 --> 00:04:38,691
In 2007,
the Spitzer Space Telescope

70
00:04:38,693 --> 00:04:40,126
captured this image --

71
00:04:40,128 --> 00:04:46,132
a ball of hot gas
behind the Eagle Nebula...

72
00:04:49,069 --> 00:04:53,606
...evidence
that a huge star has exploded

73
00:04:53,608 --> 00:04:59,345
and sent a vast wall of gas
racing toward the pillars.

74
00:04:59,347 --> 00:05:01,448
There's a wave of hot material

75
00:05:01,450 --> 00:05:03,216
approaching
the pillars of creation,

76
00:05:03,218 --> 00:05:05,351
and this may be a shock wave
from a supernova,

77
00:05:05,353 --> 00:05:06,419
a dying star.

78
00:05:10,858 --> 00:05:16,963
Supernovas briefly
outshine entire galaxies.

79
00:05:16,965 --> 00:05:21,267
Superheated plasma blasts
into space

80
00:05:21,269 --> 00:05:24,504
at 70 million miles per hour.

81
00:05:24,506 --> 00:05:31,377
A mighty shock wave speeds
toward the pillars of creation.

82
00:05:37,384 --> 00:05:41,855
When it hits,
it will demolish them.

83
00:05:41,857 --> 00:05:47,160
It will also create new worlds.

84
00:05:47,162 --> 00:05:51,431
Supernova shock waves smash
into the pillars,

85
00:05:51,433 --> 00:05:54,734
compressing
the thin gas and dust

86
00:05:54,736 --> 00:05:58,137
into dense clumps.

87
00:05:58,139 --> 00:06:05,011
Each is a new star,
a new solar system.

88
00:06:05,013 --> 00:06:07,447
Molecular cloud minding
its own business

89
00:06:07,449 --> 00:06:10,149
gets blasted
by a supernova explosion,

90
00:06:10,151 --> 00:06:15,555
crushing the cloud
down into stars and planets.

91
00:06:15,557 --> 00:06:19,425
Wind back 4 1/2 billion years,

92
00:06:19,427 --> 00:06:24,631
and our solar system starts
the same way.

93
00:06:24,633 --> 00:06:28,568
A supernova crushes
a massive dusty cloud

94
00:06:28,570 --> 00:06:33,006
into a protoplanetary disk.

95
00:06:33,008 --> 00:06:35,975
A thin nebulous cloud becomes

96
00:06:35,977 --> 00:06:39,946
a dense whirlpool
of gas and dust --

97
00:06:39,948 --> 00:06:45,552
a solar system in the making.

98
00:06:45,554 --> 00:06:48,321
One star is destroyed.

99
00:06:48,323 --> 00:06:51,691
A new star is born --

100
00:06:51,693 --> 00:06:56,462
our sun and its planets.

101
00:06:56,464 --> 00:06:58,298
This is the first link

102
00:06:58,300 --> 00:07:01,634
in the long and unlikely
chain of events

103
00:07:01,636 --> 00:07:03,836
that made our world.

104
00:07:06,273 --> 00:07:09,609
For Earth to even be here,

105
00:07:09,611 --> 00:07:14,347
we had to beat
astronomical odds.

106
00:07:14,349 --> 00:07:17,684
A host of different factors
have to line up

107
00:07:17,686 --> 00:07:19,852
to get a planet
just like the Earth.

108
00:07:19,854 --> 00:07:21,621
You have to have
the right distance,

109
00:07:21,623 --> 00:07:24,057
the right size,
the right kind of moon.

110
00:07:26,694 --> 00:07:31,898
On Earth, all the conditions are
just right for life.

111
00:07:31,900 --> 00:07:35,101
To get a world like ours,
you need a lot of aces.

112
00:07:35,103 --> 00:07:38,338
Somehow, our solar system hit
the jackpot.

113
00:07:38,340 --> 00:07:42,175
But the big question is
did it happen anywhere else?

114
00:07:45,813 --> 00:07:50,183
One of the Universe's
most violent events

115
00:07:50,185 --> 00:07:55,288
triggered
the birth of our planet.

116
00:07:55,290 --> 00:08:00,660
A sparse cloud crushed
into a dense swirl of dust.

117
00:08:02,663 --> 00:08:08,167
Some of this dust will become
planet Earth.

118
00:08:08,169 --> 00:08:14,173
But how do tiny dust grains
create entire worlds?

119
00:08:24,527 --> 00:08:28,963
A supernova explosion
triggers a chain of events

120
00:08:28,965 --> 00:08:31,866
that will eventually create
the Earth...

121
00:08:33,969 --> 00:08:37,038
...the formation
of our solar system.

122
00:08:39,408 --> 00:08:44,312
A hot ball of gas grows
in the center.

123
00:08:44,314 --> 00:08:50,185
This will become our Sun.

124
00:08:50,187 --> 00:08:54,722
The dust that swirls around it
will form the planets.

125
00:08:56,559 --> 00:09:01,296
But first,
the grains must stick together.

126
00:09:01,298 --> 00:09:03,898
So, we have this
interesting conundrum, right?

127
00:09:03,900 --> 00:09:07,235
So, this disk consists
of gas and dust particles.

128
00:09:07,237 --> 00:09:09,437
They're about the size of,
let's say,

129
00:09:09,439 --> 00:09:11,039
particles in smoke, all right?

130
00:09:11,041 --> 00:09:12,941
We'll say cigarette smoke,
right?

131
00:09:12,943 --> 00:09:14,375
So, these are small things.

132
00:09:14,377 --> 00:09:18,746
And, somehow, we have to get
from those little grains

133
00:09:18,748 --> 00:09:20,014
to what we see on the Earth.

134
00:09:20,016 --> 00:09:25,386
Gravity is
a powerful attractive force.

135
00:09:25,388 --> 00:09:30,291
It shapes
galaxies and solar systems,

136
00:09:30,293 --> 00:09:33,661
but specks of dust are
far too small

137
00:09:33,663 --> 00:09:36,764
to pull on each other.

138
00:09:36,766 --> 00:09:41,636
Somehow, they clump together
to form planets.

139
00:09:41,638 --> 00:09:45,940
So, if gravity doesn't
bind them, what does?

140
00:09:48,477 --> 00:09:51,613
In Germany,
scientists are on the case.

141
00:09:53,349 --> 00:09:54,415
Okay.

142
00:09:54,417 --> 00:09:58,286
They can simulate
how dust behaves in space

143
00:09:58,288 --> 00:10:02,624
inside a huge tower.

144
00:10:02,626 --> 00:10:04,525
Here, we do
free-fall experiments.

145
00:10:04,527 --> 00:10:06,794
So,
the whole experimental setup,

146
00:10:06,796 --> 00:10:10,265
including our dust aggregates,
are in perfect free fall.

147
00:10:10,267 --> 00:10:13,735
It is simulation of space,
but a very good one, indeed.

148
00:10:13,737 --> 00:10:16,804
I think this is the closest
you can get to space on Earth.

149
00:10:17,806 --> 00:10:22,043
Researchers place dust
in the container

150
00:10:22,045 --> 00:10:24,946
and load it
into a launch capsule.

151
00:10:27,016 --> 00:10:29,217
At the base of the tower,

152
00:10:29,219 --> 00:10:32,921
they lower it
into a super-powerful catapult.

153
00:10:32,923 --> 00:10:37,458
This launches
the half-ton capsule

154
00:10:37,460 --> 00:10:41,296
from zero
to over 100 miles per hour

155
00:10:41,298 --> 00:10:43,331
in a quarter of a second.

156
00:10:46,635 --> 00:10:47,835
400 feet up,

157
00:10:47,837 --> 00:10:51,406
the capsule reaches
the top of the tower,

158
00:10:51,408 --> 00:10:54,909
then plunges back down.

159
00:10:54,911 --> 00:11:01,049
A drum of polystyrene balls,
30 feet deep, breaks its fall.

160
00:11:03,552 --> 00:11:08,089
All this gives
just 10 seconds of zero gravity,

161
00:11:08,091 --> 00:11:12,794
just enough time, they hope,
for the dust to stick.

162
00:11:12,796 --> 00:11:16,164
Three, two, one, and go.

163
00:11:18,901 --> 00:11:22,403
Moments after
the capsule launches,

164
00:11:22,405 --> 00:11:24,706
the dust inside becomes
weightless.

165
00:11:27,343 --> 00:11:29,677
The grains clump together,

166
00:11:29,679 --> 00:11:32,814
just like
the early solar system.

167
00:11:39,855 --> 00:11:41,990
These images reveal

168
00:11:41,992 --> 00:11:47,729
how dust particles came together
4 1/2 billion years ago

169
00:11:47,731 --> 00:11:50,631
to form the Earth.

170
00:11:50,633 --> 00:11:52,467
The force that binds
the aggregates together

171
00:11:52,469 --> 00:11:53,701
is not gravity.

172
00:11:53,703 --> 00:11:56,938
They are too small
for gravity to be efficient.

173
00:11:56,940 --> 00:12:01,843
We think the force that binds
the aggregates together

174
00:12:01,845 --> 00:12:04,045
is electrostatic force.

175
00:12:04,047 --> 00:12:05,980
It's the same reason

176
00:12:05,982 --> 00:12:09,217
that when you pull
your clothes out of the dryer --

177
00:12:09,219 --> 00:12:11,753
you know how the clothes
sometimes stick to you?

178
00:12:11,755 --> 00:12:14,322
That's the same effect
that allows

179
00:12:14,324 --> 00:12:17,125
one dust particle
to stick to another.

180
00:12:17,127 --> 00:12:21,562
Dust particles join
to form balls of fluff.

181
00:12:21,564 --> 00:12:24,132
The little static charges
that they have

182
00:12:24,134 --> 00:12:25,800
can make them stick
when they hit,

183
00:12:25,802 --> 00:12:28,002
and you get something
sort of like the dust bunnies

184
00:12:28,004 --> 00:12:29,771
that I have a lot of
underneath my bed.

185
00:12:29,773 --> 00:12:36,711
These cosmic dust bunnies are
planets in the making.

186
00:12:37,880 --> 00:12:41,416
They start out
smaller than a pinhead,

187
00:12:41,418 --> 00:12:43,317
then grow.

188
00:12:43,319 --> 00:12:47,255
The dust is now in clumps,

189
00:12:47,257 --> 00:12:53,194
but it's still
just balls of dust.

190
00:12:53,196 --> 00:12:58,266
Turning dust balls into rocks
takes a whole new process...

191
00:13:00,335 --> 00:13:03,571
...a cosmic electric storm.

192
00:13:06,542 --> 00:13:13,247
Space clouds build up charge
just like clouds here on Earth,

193
00:13:13,249 --> 00:13:16,250
generating
huge bolts of lightning.

194
00:13:19,254 --> 00:13:22,490
Balls of dust can
turn into solid rocks

195
00:13:22,492 --> 00:13:25,893
by an energetic event,
like lightning.

196
00:13:25,895 --> 00:13:30,298
The electric bolts
smash through the dust balls

197
00:13:30,300 --> 00:13:33,901
and heat them
to 3,000 degrees Fahrenheit.

198
00:13:37,139 --> 00:13:42,844
In minutes, they cool and fuse
into solid rock.

199
00:13:42,846 --> 00:13:48,382
Meteorites today still carry
these ancient rock balls

200
00:13:48,384 --> 00:13:50,818
inside them.

201
00:13:50,820 --> 00:13:52,954
These tiny globules

202
00:13:52,956 --> 00:13:57,358
were once the building blocks
of planets.

203
00:13:57,360 --> 00:13:59,961
To form the Earth,

204
00:13:59,963 --> 00:14:06,434
these tiny balls must collide,
stick, and grow.

205
00:14:06,436 --> 00:14:09,036
Rocks begin to build up
by accidental collisions,

206
00:14:09,038 --> 00:14:10,505
which can take a long time.

207
00:14:10,507 --> 00:14:13,774
Eventually, the protoplanets,
as we call them --

208
00:14:13,776 --> 00:14:14,976
the baby planets --

209
00:14:14,978 --> 00:14:19,614
get the size of asteroids,
kilometers across.

210
00:14:19,616 --> 00:14:24,719
The baby earth is now the size
of a few city blocks,

211
00:14:24,721 --> 00:14:28,289
big enough for a new force
to take charge --

212
00:14:28,291 --> 00:14:30,658
gravity.

213
00:14:30,660 --> 00:14:32,026
At that point,

214
00:14:32,028 --> 00:14:35,463
a single asteroid will
gravitationally attract

215
00:14:35,465 --> 00:14:37,231
a neighboring asteroid.

216
00:14:37,233 --> 00:14:39,033
And, so, those two asteroids

217
00:14:39,035 --> 00:14:41,402
that would have
passed in the night

218
00:14:41,404 --> 00:14:44,872
are gravitationally attracted,
and they hit each other.

219
00:14:47,109 --> 00:14:49,377
Once gravity starts
to rear its head,

220
00:14:49,379 --> 00:14:50,645
things really speed up

221
00:14:50,647 --> 00:14:53,748
because instead of just randomly
plowing through material

222
00:14:53,750 --> 00:14:55,283
and getting bigger that way,

223
00:14:55,285 --> 00:14:57,485
now it's starting
to draw material in.

224
00:14:59,621 --> 00:15:05,726
Gravity pulls rocks together,
then holds them there

225
00:15:05,728 --> 00:15:11,365
to produce bigger and bigger
piles of rubble.

226
00:15:11,367 --> 00:15:14,402
So, this formation process,
which was taking a long time

227
00:15:14,404 --> 00:15:16,771
to get to the size
where gravity kicks in,

228
00:15:16,773 --> 00:15:18,973
suddenly gets
kicked into overdrive,

229
00:15:18,975 --> 00:15:21,309
and the planet grows
very rapidly.

230
00:15:22,504 --> 00:15:26,748
But planets are more
than just overgrown rock piles.

231
00:15:29,385 --> 00:15:33,020
These rocks are lumpy and inert.

232
00:15:33,022 --> 00:15:37,725
How did the Earth become
round and full of life?

233
00:15:46,927 --> 00:15:52,265
The early solar system is
a construction site for planets.

234
00:15:53,934 --> 00:15:56,736
Dust sticks together
to form rocks.

235
00:15:56,738 --> 00:16:01,774
Rocks join to form asteroids.

236
00:16:01,776 --> 00:16:07,780
But most asteroids
look nothing like Earth.

237
00:16:07,782 --> 00:16:10,583
And when you look at a close-up
of an asteroid,

238
00:16:10,585 --> 00:16:13,419
it looks like
some kind of distorted peanut,

239
00:16:13,421 --> 00:16:15,855
like a potato that's been
sort of bashed.

240
00:16:15,857 --> 00:16:19,559
You can see
giant craters and oblong shapes.

241
00:16:19,561 --> 00:16:23,896
The young Earth is one
of billions

242
00:16:23,898 --> 00:16:28,334
of misshapen space boulders.

243
00:16:28,336 --> 00:16:32,071
To become a planet,
it must first become round.

244
00:16:32,073 --> 00:16:36,142
That process only starts

245
00:16:36,144 --> 00:16:40,279
when it's several hundred miles
across,

246
00:16:40,281 --> 00:16:46,118
when its own internal gravity
begins to change its shape.

247
00:16:49,256 --> 00:16:52,224
Once you get enough material,
enough mass,

248
00:16:52,226 --> 00:16:54,560
the gravitational force becomes
stronger.

249
00:16:54,562 --> 00:16:57,229
Any giant mountain will be
crushed down

250
00:16:57,231 --> 00:16:59,899
by the force of gravity.

251
00:16:59,901 --> 00:17:02,001
The gravity is so strong

252
00:17:02,003 --> 00:17:03,903
that it can
actually break rocks,

253
00:17:03,905 --> 00:17:06,305
and the rocks, itself,
can act like a fluid,

254
00:17:06,307 --> 00:17:07,773
making an object round.

255
00:17:09,977 --> 00:17:15,781
Huge outcrops of rock
crumble and fall.

256
00:17:15,783 --> 00:17:19,285
The immense self-gravity
of the early Earth

257
00:17:19,287 --> 00:17:24,991
crushes it
into the most efficient shape --

258
00:17:24,993 --> 00:17:28,728
a vast, round ball of rock...

259
00:17:32,065 --> 00:17:34,867
...a lopsided pile of rubble

260
00:17:34,869 --> 00:17:38,704
transformed
into a miniature world.

261
00:17:43,944 --> 00:17:46,445
The Earth has a new shape,

262
00:17:46,447 --> 00:17:49,982
but it's still
just a ball of rock.

263
00:17:49,984 --> 00:17:54,353
Its structure will
also soon change.

264
00:17:54,355 --> 00:18:01,761
Cosmic rocks and boulders
still rain down from space.

265
00:18:01,763 --> 00:18:05,064
Each collision heats the ground.

266
00:18:05,066 --> 00:18:07,099
There's a huge amount of energy

267
00:18:07,101 --> 00:18:09,168
stored in an object
that's moving rapidly.

268
00:18:09,170 --> 00:18:10,369
And when that hits the Earth,

269
00:18:10,371 --> 00:18:12,371
all that energy is dumped
into the material,

270
00:18:12,373 --> 00:18:13,973
and that heats it up
and melts it.

271
00:18:13,975 --> 00:18:15,941
And the Earth became molten

272
00:18:15,943 --> 00:18:18,711
and stayed that way
for a long time.

273
00:18:18,713 --> 00:18:22,615
The young planet is
no longer solid rock.

274
00:18:22,617 --> 00:18:25,351
It's a seething molten mass...

275
00:18:28,321 --> 00:18:30,756
...just like this blast furnace

276
00:18:30,758 --> 00:18:33,893
at the Severstal plant
in Detroit.

277
00:18:38,065 --> 00:18:39,398
Believe it or not,

278
00:18:39,400 --> 00:18:43,202
this process behind me makes
life on Earth possible.

279
00:18:45,439 --> 00:18:48,874
They feed in ground-up iron ore,

280
00:18:48,876 --> 00:18:51,210
a mixture of rock and metal...

281
00:18:53,013 --> 00:18:56,649
...just like the early Earth.

282
00:19:01,121 --> 00:19:06,859
Put iron ore in a furnace,
and the heat melts everything.

283
00:19:09,696 --> 00:19:15,468
This molten iron is
at 2,700 degrees Fahrenheit.

284
00:19:15,470 --> 00:19:18,404
That's about the temperature
of the surface of the Earth

285
00:19:18,406 --> 00:19:21,073
4 1/2 billion years ago.

286
00:19:21,075 --> 00:19:25,044
Imagine an entire planet molten.

287
00:19:25,046 --> 00:19:26,946
In the distance, you would see

288
00:19:26,948 --> 00:19:30,382
thundering volcanoes
spewing out lava.

289
00:19:30,384 --> 00:19:34,386
It would be a scene
right out of Dante's "Inferno."

290
00:19:40,694 --> 00:19:42,928
Iron is heavier than rock.

291
00:19:42,930 --> 00:19:47,566
Now molten, they separate.

292
00:19:47,568 --> 00:19:50,603
This is amazing.

293
00:19:50,605 --> 00:19:52,104
We're witnessing a process

294
00:19:52,106 --> 00:19:54,507
which created
the very crust of the Earth

295
00:19:54,509 --> 00:19:55,908
billions of years ago --

296
00:19:55,910 --> 00:19:58,077
the crust
that we walk on every day.

297
00:20:00,313 --> 00:20:07,219
Molten rock rises to the surface
and cools to form the crust.

298
00:20:07,221 --> 00:20:11,557
Molten iron sinks underneath.

299
00:20:11,559 --> 00:20:13,159
Inside the Earth,

300
00:20:13,161 --> 00:20:17,062
it sank all the way
to the planet's core.

301
00:20:17,064 --> 00:20:21,500
The rocky surface is
where we live.

302
00:20:21,502 --> 00:20:25,704
But without Earth's
molten iron core,

303
00:20:25,706 --> 00:20:29,341
none of us could survive.

304
00:20:29,343 --> 00:20:34,513
This process separated the iron
from the rocky minerals.

305
00:20:34,515 --> 00:20:37,716
As the iron descended
to the center of the Earth,

306
00:20:37,718 --> 00:20:40,352
it eventually created
a magnetic field,

307
00:20:40,354 --> 00:20:42,421
and that's why we're here today.

308
00:20:43,023 --> 00:20:48,927
The molten iron swirls
inside the Earth's core

309
00:20:48,929 --> 00:20:52,353
and generates
a powerful magnetic field

310
00:20:52,354 --> 00:20:54,687
around the planet --

311
00:20:55,769 --> 00:21:02,674
a cosmic shield against
deadly radiation from space.

312
00:21:02,676 --> 00:21:08,713
But the young Earth is
still small --

313
00:21:08,715 --> 00:21:12,818
far smaller than the Moon today.

314
00:21:12,820 --> 00:21:17,823
This newly-formed world
must grow.

315
00:21:20,526 --> 00:21:24,696
It must also avoid
being blown to pieces.

316
00:21:24,698 --> 00:21:28,500
Thousands of protoplanets

317
00:21:28,502 --> 00:21:32,204
are hurtling
around the solar system,

318
00:21:32,206 --> 00:21:36,274
and some are heading
straight for Earth.

319
00:21:45,634 --> 00:21:51,029
It's 100,000 years
since our solar system formed.

320
00:21:51,129 --> 00:21:55,298
The young Earth
already looks like a planet.

321
00:21:55,300 --> 00:21:56,933
It's round.

322
00:21:56,935 --> 00:22:01,938
It has an iron core
and a rocky surface.

323
00:22:01,940 --> 00:22:08,711
Yet, our baby planet is
just a few hundred miles across.

324
00:22:08,713 --> 00:22:12,315
It has a long way to go.

325
00:22:12,317 --> 00:22:18,487
It must grow
4,000 times more massive,

326
00:22:18,489 --> 00:22:21,924
and it has competition.

327
00:22:21,926 --> 00:22:28,064
Thousands of other protoplanets
shoot through the solar system,

328
00:22:28,066 --> 00:22:33,069
often colliding
at over 20,000 miles per hour.

329
00:22:35,472 --> 00:22:40,243
You can find proof
of this ancient destructive era

330
00:22:40,245 --> 00:22:42,144
in modern-day Arizona.

331
00:22:42,146 --> 00:22:50,119
Not meteor crater itself --
that's just 50,000 years old --

332
00:22:50,121 --> 00:22:54,190
but the asteroid
that gouged it out.

333
00:22:54,192 --> 00:22:59,862
That was
4 1/2 billion years old.

334
00:22:59,864 --> 00:23:02,865
Mark Sykes and Marvin Killgore

335
00:23:02,867 --> 00:23:07,403
think the asteroid came
from a violent event

336
00:23:07,405 --> 00:23:09,672
in the early solar system.

337
00:23:11,908 --> 00:23:16,912
The asteroid flew through space
for billions of years,

338
00:23:16,914 --> 00:23:20,583
then it hit Earth.

339
00:23:20,585 --> 00:23:25,621
They aim to find
a fragment of the asteroid,

340
00:23:25,623 --> 00:23:30,493
a remnant from the period
of planetary formation.

341
00:23:32,563 --> 00:23:35,364
About six miles from here is
meteor crater,

342
00:23:35,366 --> 00:23:39,669
and that was an impact
50,000 years or so ago,

343
00:23:39,671 --> 00:23:43,172
and it spewed
a bunch of pieces out.

344
00:23:43,174 --> 00:23:44,674
They're convinced

345
00:23:44,676 --> 00:23:48,511
the original asteroid was
rich in iron,

346
00:23:48,513 --> 00:23:50,112
so they've come prepared

347
00:23:50,114 --> 00:23:53,549
with some
impressive metal detectors.

348
00:23:53,551 --> 00:23:54,717
Does it work?

349
00:23:54,719 --> 00:23:56,285
Oh, yeah.

350
00:24:00,224 --> 00:24:01,991
That's the sound
we're listening for.

351
00:24:06,330 --> 00:24:10,700
But even with a quad-drawn
metal detector,

352
00:24:10,702 --> 00:24:14,203
meteorites are hard to find.

353
00:24:16,206 --> 00:24:19,642
Yeah, are you pretty convinced
there's nothing there?

354
00:24:19,644 --> 00:24:22,778
Yeah, I don't really --
I'm not detecting anything.

355
00:24:26,683 --> 00:24:30,419
They find metal
but no meteorites.

356
00:24:30,421 --> 00:24:32,955
My great discovery
of the afternoon

357
00:24:32,957 --> 00:24:37,360
has been this bolt...

358
00:24:37,362 --> 00:24:38,928
and this piece of wire.

359
00:24:45,402 --> 00:24:52,041
It takes hours of searching
and many false alarms.

360
00:24:52,043 --> 00:24:56,912
Then, with the light fading,
the detector sounds again.

361
00:25:02,552 --> 00:25:05,421
How about that?
Success at last.

362
00:25:05,423 --> 00:25:11,293
This meteorite is
over 90% iron and nickle.

363
00:25:11,295 --> 00:25:12,928
It could only form

364
00:25:12,930 --> 00:25:16,098
right in the core
of a protoplanet.

365
00:25:16,100 --> 00:25:18,834
The protoplanet it came from

366
00:25:18,836 --> 00:25:23,439
must have smashed apart
in a brutal collision.

367
00:25:23,441 --> 00:25:28,778
Well, in the early solar system,
it was a pretty violent place,

368
00:25:28,780 --> 00:25:33,048
and these protoplanetary embryos
would smash into each other.

369
00:25:33,050 --> 00:25:35,217
They would shatter each other,

370
00:25:35,219 --> 00:25:38,120
exposing
the interior cores like this.

371
00:25:38,122 --> 00:25:40,222
It was a very tumultuous time.

372
00:25:40,224 --> 00:25:47,630
Entire worlds reduced
to chunks of rock and metal

373
00:25:47,632 --> 00:25:52,601
and scattered into outer space.

374
00:25:52,603 --> 00:25:54,970
In the early solar system,

375
00:25:54,972 --> 00:25:59,742
these vast collisions
are common.

376
00:25:59,744 --> 00:26:04,079
The young Earth is in danger.

377
00:26:04,081 --> 00:26:09,952
The period's name is
the "Titanomachia" --

378
00:26:09,954 --> 00:26:13,956
literally
the "War of the Titans."

379
00:26:16,326 --> 00:26:19,361
All rocky planets,
the Earth included,

380
00:26:19,363 --> 00:26:24,834
go through
this destructive phase.

381
00:26:24,836 --> 00:26:28,437
Sometimes,
they shatter completely.

382
00:26:28,439 --> 00:26:32,875
Sometimes,
one consumes the other.

383
00:26:32,877 --> 00:26:35,878
All the big guys are sort of
competing with one another

384
00:26:35,880 --> 00:26:38,180
in a very violent way, actually,

385
00:26:38,182 --> 00:26:42,384
to see who comes out on top
by eating all their neighbors.

386
00:26:42,386 --> 00:26:48,824
The battle lasts
over 30 million years.

387
00:26:48,826 --> 00:26:52,962
Finally, thousands
of protoplanets have combined

388
00:26:52,964 --> 00:26:57,967
into a few full-size planets --

389
00:26:57,969 --> 00:27:06,775
Mercury, Venus, Earth, Mars,
and a fifth planet, Thea.

390
00:27:06,777 --> 00:27:12,715
It's racing toward earth --

391
00:27:12,717 --> 00:27:16,852
our planet's last giant impact.

392
00:27:18,855 --> 00:27:25,117
Thea is the size of Mars --
big enough to destroy the Earth.

393
00:27:27,164 --> 00:27:28,964
If that thing had
hit us straight on,

394
00:27:28,966 --> 00:27:31,166
it could have literally
blown the Earth to bits,

395
00:27:31,168 --> 00:27:33,369
and then we wouldn't even have
a planet today.

396
00:27:33,371 --> 00:27:37,039
If this Mars-like object had
a direct hit with the Earth,

397
00:27:37,041 --> 00:27:39,775
perhaps there would have been
another asteroid belt

398
00:27:39,777 --> 00:27:41,143
where the Earth is today.

399
00:27:41,145 --> 00:27:45,481
But Earth is in luck.

400
00:27:45,483 --> 00:27:51,787
Instead of a head-on crash,
Thea strikes a glancing blow.

401
00:27:55,959 --> 00:28:01,363
It's the most violent event
the Earth has ever known.

402
00:28:04,801 --> 00:28:10,272
The impact turns the Earth
back to a molten world,

403
00:28:10,274 --> 00:28:15,844
a vast magma ocean
600 miles deep.

404
00:28:18,949 --> 00:28:21,684
The Earth barely survives.

405
00:28:26,623 --> 00:28:31,193
And the encounter changes
our world forever.

406
00:28:33,597 --> 00:28:38,267
Material blasts
out into space --

407
00:28:38,269 --> 00:28:44,840
enough rock to build
a mountain as wide as America

408
00:28:44,842 --> 00:28:48,877
and 10,000 miles high.

409
00:28:48,879 --> 00:28:50,346
There would have been
so much energy,

410
00:28:50,348 --> 00:28:51,347
so much catastrophe.

411
00:28:51,349 --> 00:28:53,616
Huge amounts of material
blasted off

412
00:28:53,618 --> 00:28:55,951
and went into orbit
around the Earth.

413
00:28:55,953 --> 00:29:01,223
The debris forms
a huge ring around the Earth.

414
00:29:01,225 --> 00:29:06,829
This gathers together
to form two rocky bodies,

415
00:29:06,831 --> 00:29:11,133
both orbiting the Earth.

416
00:29:11,135 --> 00:29:13,135
Something the size of Mars
hit the Earth

417
00:29:13,137 --> 00:29:14,503
about 4 billion years ago.

418
00:29:14,505 --> 00:29:16,872
Lots of material would have been
thrown off.

419
00:29:16,874 --> 00:29:18,073
We now think
that it may have formed

420
00:29:18,075 --> 00:29:20,609
not only one moon but two.

421
00:29:20,611 --> 00:29:24,346
For millions of years,

422
00:29:24,348 --> 00:29:28,250
two moons dominate
the Earth's sky.

423
00:29:30,820 --> 00:29:35,791
Eventually,
they drift together and collide.

424
00:29:42,499 --> 00:29:49,004
Two moons merge into one --

425
00:29:49,006 --> 00:29:53,742
the massive moon we see today.

426
00:29:53,744 --> 00:29:55,411
There's no other planet
that we know of

427
00:29:55,413 --> 00:29:57,146
that has a moon as large as ours

428
00:29:57,148 --> 00:29:59,448
in comparison
to the size of the planet.

429
00:29:59,450 --> 00:30:00,949
We're almost a binary planet --

430
00:30:00,951 --> 00:30:02,818
two worlds going
around each other.

431
00:30:02,820 --> 00:30:09,458
Without this large moon,
we might not even be here.

432
00:30:11,461 --> 00:30:13,462
The moon plays a key role

433
00:30:13,464 --> 00:30:16,865
in the survival of life
here on the Earth.

434
00:30:16,867 --> 00:30:19,735
And the reason is that the Moon,
in its orbit,

435
00:30:19,737 --> 00:30:23,172
stabilizes the Earth.

436
00:30:23,174 --> 00:30:28,377
The Moon keeps the Earth
spinning at the same angle.

437
00:30:28,379 --> 00:30:31,847
That steadies our climate.

438
00:30:31,849 --> 00:30:34,950
The fact that the Earth's axis
stays in the same direction

439
00:30:34,952 --> 00:30:37,519
as it goes around the sun
produces the seasons,

440
00:30:37,521 --> 00:30:38,987
but regular seasons --

441
00:30:38,989 --> 00:30:43,058
things that life can depend upon
as it evolves.

442
00:30:43,060 --> 00:30:49,131
Earth is neither too hot
nor too cold for life

443
00:30:49,133 --> 00:30:51,133
thanks to our distance
from the Sun

444
00:30:51,135 --> 00:30:54,603
and our massive moon.

445
00:30:59,075 --> 00:31:04,213
The Earth is not covered
in ice or steam

446
00:31:04,215 --> 00:31:05,814
but in liquid water.

447
00:31:09,319 --> 00:31:14,957
Yet, that water must come
from somewhere.

448
00:31:14,959 --> 00:31:17,893
The newly formed earth is dry.

449
00:31:20,330 --> 00:31:26,568
To get water, our planet must,
once again, face disaster.

450
00:31:36,252 --> 00:31:42,224
It's half a billion years
since the Sun first ignited.

451
00:31:42,226 --> 00:31:44,560
Four billion years from now,

452
00:31:44,562 --> 00:31:48,063
the first humans will
set foot on Earth.

453
00:31:50,400 --> 00:31:56,705
The Moon has just formed,
and the Earth is a desert.

454
00:32:01,144 --> 00:32:03,312
One of the more amazing ideas
in astronomy

455
00:32:03,314 --> 00:32:05,781
is that the Earth started out
hot and dry.

456
00:32:05,783 --> 00:32:07,783
There was
no water here originally.

457
00:32:07,785 --> 00:32:11,153
As the planets formed,

458
00:32:11,155 --> 00:32:15,758
the Sun's intense radiation
vaporized the water

459
00:32:15,760 --> 00:32:18,794
in the inner solar system.

460
00:32:18,796 --> 00:32:23,432
Farther from the Sun,
temperatures were cooler.

461
00:32:23,434 --> 00:32:25,467
So in the outer solar system,

462
00:32:25,469 --> 00:32:30,205
ice and water collected
on comets and asteroids.

463
00:32:32,208 --> 00:32:39,081
While closer to the Sun,
the young Earth was dry.

464
00:32:39,083 --> 00:32:41,684
So, things changed.
What happened?

465
00:32:41,686 --> 00:32:44,987
How is that now we have
this wonderful water cycle?

466
00:32:44,989 --> 00:32:47,456
Well, the water probably came
from somewhere else.

467
00:32:47,458 --> 00:32:49,324
Well, if you want to have

468
00:32:49,326 --> 00:32:51,794
a solar system that has
a lot of water in it,

469
00:32:51,796 --> 00:32:54,363
you have to bring it
from the outer parts

470
00:32:54,365 --> 00:32:55,931
down into the inner parts,

471
00:32:55,933 --> 00:32:58,901
and you can do that
through comets and asteroids.

472
00:33:00,913 --> 00:33:06,769
Comets and icy asteroids contain
huge reserves of water,

473
00:33:07,411 --> 00:33:12,948
but they're hundreds of millions
of miles from the young Earth.

474
00:33:12,950 --> 00:33:17,119
Then something changes --

475
00:33:17,121 --> 00:33:21,356
an event that tosses
the asteroids and comets

476
00:33:21,358 --> 00:33:23,992
right across the solar system.

477
00:33:25,562 --> 00:33:31,633
Jupiter, Saturn, Neptune, Uranus

478
00:33:31,635 --> 00:33:37,539
take
a cosmic roller-coaster ride.

479
00:33:37,541 --> 00:33:40,275
So, this is
an event that happened

480
00:33:40,277 --> 00:33:42,077
when the solar system was young.

481
00:33:42,079 --> 00:33:44,913
Think of it as more
of its teenage breakout years

482
00:33:44,915 --> 00:33:47,316
where it just started
to party for a while.

483
00:33:47,318 --> 00:33:54,923
The young planets have not yet
settled into stable orbits.

484
00:33:54,925 --> 00:33:56,725
As their orbits shift,

485
00:33:56,727 --> 00:34:02,831
Jupiter and Saturn fall
into an intricate dance.

486
00:34:02,833 --> 00:34:06,769
Every time
Saturn orbits the Sun once,

487
00:34:06,771 --> 00:34:10,172
Jupiter orbits twice,

488
00:34:10,174 --> 00:34:13,876
so they always line up
at the same spot.

489
00:34:13,878 --> 00:34:18,680
Each time, gravity tugs them
in the same direction.

490
00:34:18,682 --> 00:34:22,284
First, they destabilize
each other

491
00:34:22,286 --> 00:34:26,421
and then
the entire solar system.

492
00:34:26,423 --> 00:34:28,423
The whole thing just goes
kaplooey.

493
00:34:28,425 --> 00:34:31,527
The analogy I like to use is
when a bowling ball hits pins,

494
00:34:31,529 --> 00:34:33,562
it just goes "bam!"
All over the place.

495
00:34:33,564 --> 00:34:34,930
That's what this would have
looked like.

496
00:34:34,932 --> 00:34:39,001
Planetary pandemonium.

497
00:34:39,003 --> 00:34:42,137
Neptune and Uranus
switch places.

498
00:34:42,139 --> 00:34:46,275
Saturn races outwards.

499
00:34:46,277 --> 00:34:50,979
The giant planets scatter
billions of asteroids and comets

500
00:34:50,981 --> 00:34:52,381
onto new paths.

501
00:34:54,450 --> 00:34:58,086
Many head for Earth.

502
00:34:58,088 --> 00:35:00,255
These asteroids and comets
would have been scattered

503
00:35:00,257 --> 00:35:02,090
all over the place, right,

504
00:35:02,092 --> 00:35:03,659
some of them hitting
the Earth and Moon.

505
00:35:03,661 --> 00:35:10,599
Cosmic missiles
bombard the Earth.

506
00:35:10,601 --> 00:35:11,800
We believe

507
00:35:11,802 --> 00:35:14,036
that every square inch
of the Earth got hit

508
00:35:14,038 --> 00:35:17,072
by a comet or an asteroid
during this period.

509
00:35:17,074 --> 00:35:19,208
It would not have been
a fun time to be here.

510
00:35:21,144 --> 00:35:27,850
The bombardment lasts
hundreds of millions of years

511
00:35:27,852 --> 00:35:32,154
until, finally,
the gas planets settle

512
00:35:32,156 --> 00:35:36,592
into the stable orbits
we see today,

513
00:35:36,594 --> 00:35:38,694
restoring order.

514
00:35:41,497 --> 00:35:46,568
But Earth itself has
fundamentally changed.

515
00:35:46,570 --> 00:35:52,441
Those comets and asteroids were
not just made of rock

516
00:35:52,443 --> 00:35:57,813
but of ice, frozen water.

517
00:35:57,815 --> 00:35:59,915
Comets, we know,
are made out of ice.

518
00:35:59,917 --> 00:36:02,084
They're dirty snowballs
in outer space,

519
00:36:02,086 --> 00:36:06,088
and even asteroids can bring
water and ice to the Earth.

520
00:36:06,090 --> 00:36:13,996
Our oceans are full
thanks to the cosmic hailstorm.

521
00:36:13,998 --> 00:36:17,633
So next time you're drinking
a glass of water, realize

522
00:36:17,635 --> 00:36:20,903
that you're probably drinking
comet and asteroid juice.

523
00:36:20,905 --> 00:36:26,008
The arrival of water
is the final step

524
00:36:26,010 --> 00:36:29,077
to create a habitable planet.

525
00:36:32,081 --> 00:36:36,285
A sequence of catastrophes has
created a world

526
00:36:36,287 --> 00:36:40,555
that's perfect for life.

527
00:36:40,557 --> 00:36:45,127
But has it happened
elsewhere among the stars?

528
00:36:45,129 --> 00:36:47,963
Or are we alone?

529
00:37:01,149 --> 00:37:04,051
How did we get here?

530
00:37:04,053 --> 00:37:07,154
Planet Earth only exists

531
00:37:07,156 --> 00:37:11,292
because of a chain
of extraordinary events,

532
00:37:12,794 --> 00:37:15,997
a lucky throw of cosmic dice.

533
00:37:18,267 --> 00:37:19,800
Five billion years ago,

534
00:37:19,802 --> 00:37:21,702
the odds would have seemed
extremely slim

535
00:37:21,704 --> 00:37:22,803
that a planet like Earth

536
00:37:22,805 --> 00:37:25,273
would form
in a rather unremarkable arm

537
00:37:25,275 --> 00:37:26,741
in the Milky Way galaxy.

538
00:37:26,743 --> 00:37:29,443
It's like
trying to throw two sixes

539
00:37:29,445 --> 00:37:32,513
but with dice
that have thousands of sides.

540
00:37:36,551 --> 00:37:40,154
We know it happened once,
else we wouldn't be here.

541
00:37:40,156 --> 00:37:44,358
But what are the odds
it happened elsewhere?

542
00:37:46,328 --> 00:37:50,364
That other planets have life?

543
00:37:50,366 --> 00:37:53,334
Life like ours needs a planet

544
00:37:53,336 --> 00:37:57,238
with the right temperature
and size,

545
00:37:57,240 --> 00:38:02,510
a stabilizing moon,
a protective magnetic field,

546
00:38:02,512 --> 00:38:06,580
and just the right amount
of water.

547
00:38:06,582 --> 00:38:10,217
The conditions must be perfect.

548
00:38:15,924 --> 00:38:18,893
Yet, amazingly, there may be

549
00:38:18,895 --> 00:38:25,066
countless earth-like planets
out there, waiting to be found.

550
00:38:25,068 --> 00:38:30,404
Thanks to the sheer scale
of the Universe,

551
00:38:30,406 --> 00:38:38,245
we may find one any day now
with the Kepler Space Telescope.

552
00:38:38,247 --> 00:38:42,083
Geoff Marcy is
mission co-investigator.

553
00:38:42,085 --> 00:38:43,985
It has only one goal,

554
00:38:43,987 --> 00:38:46,887
and that's to discover
earth-size planets

555
00:38:46,889 --> 00:38:50,324
around other stars
that you see in the night sky.

556
00:38:50,326 --> 00:38:55,629
Earth-size planets are
hard to spot.

557
00:38:55,631 --> 00:38:59,500
Before Kepler,
astronomers took 20 years

558
00:38:59,502 --> 00:39:03,804
to discover around 500 planets.

559
00:39:03,806 --> 00:39:05,539
Most were gas giants

560
00:39:05,541 --> 00:39:08,709
hundreds of times bigger
than Earth.

561
00:39:08,711 --> 00:39:14,448
Since Kepler,
that number has exploded.

562
00:39:14,450 --> 00:39:17,118
Kepler has already discovered

563
00:39:17,120 --> 00:39:20,621
a couple thousand
planet candidates.

564
00:39:20,623 --> 00:39:23,924
Many of them are members
of multi-planet systems --

565
00:39:23,926 --> 00:39:26,827
two, three, four, five,
and even six planets

566
00:39:26,829 --> 00:39:29,130
all orbiting the same star.

567
00:39:29,132 --> 00:39:32,633
So, we're finding
an absolute avalanche of planets

568
00:39:32,635 --> 00:39:34,635
out there among the stars.

569
00:39:34,637 --> 00:39:42,076
Kepler has found one planet
only twice the size of Earth

570
00:39:42,078 --> 00:39:45,880
and the right temperature
for life.

571
00:39:45,882 --> 00:39:51,519
We don't know yet if this planet
has other earth-like attributes,

572
00:39:51,521 --> 00:39:54,989
like liquid water.

573
00:39:54,991 --> 00:39:57,124
But even if it doesn't,

574
00:39:57,126 --> 00:40:00,694
there are
many more planets out there.

575
00:40:00,696 --> 00:40:06,967
Kepler has found
only a tiny fraction of them

576
00:40:06,969 --> 00:40:12,273
because it only looks
at a small part of the sky.

577
00:40:12,275 --> 00:40:13,908
It's not even looking
at the whole sky.

578
00:40:13,910 --> 00:40:16,677
It's looking
at a very tiny slice of stars

579
00:40:16,679 --> 00:40:17,778
in the galaxy.

580
00:40:17,780 --> 00:40:19,513
And, in fact,
if you were to look up,

581
00:40:19,515 --> 00:40:21,348
you could cover it
with just your thumb.

582
00:40:21,350 --> 00:40:29,223
In the whole of our galaxy,
there are 200 billion stars.

583
00:40:29,225 --> 00:40:31,959
Many will have planets.

584
00:40:31,961 --> 00:40:35,296
Based on our knowledge
from Kepler and other searches,

585
00:40:35,298 --> 00:40:37,531
something like
half of those stars,

586
00:40:37,533 --> 00:40:40,401
perhaps even more,
harbor planets.

587
00:40:40,403 --> 00:40:45,239
That means
at least 100 billion planets

588
00:40:45,241 --> 00:40:49,577
have formed in the Milky Way.

589
00:40:49,579 --> 00:40:52,580
Earth-like worlds may be rare,

590
00:40:52,582 --> 00:40:57,785
but it seems a safe bet
they're out there somewhere.

591
00:40:57,787 --> 00:41:00,387
So, the odds of getting
an earth-like planet

592
00:41:00,389 --> 00:41:02,022
are extremely small --

593
00:41:02,024 --> 00:41:05,726
much smaller than getting
a double six at craps.

594
00:41:05,728 --> 00:41:10,231
But if you have a lot of dice,
you're guaranteed to get sixes.

595
00:41:10,233 --> 00:41:14,869
And if you have
a lot of planets,

596
00:41:14,871 --> 00:41:17,505
you're guaranteed to get earths.

597
00:41:20,275 --> 00:41:23,944
There are
so many planets in our galaxy,

598
00:41:23,946 --> 00:41:27,648
even if the chances are
one in a million,

599
00:41:27,650 --> 00:41:32,052
there should be
thousands of earth-like worlds.

600
00:41:34,122 --> 00:41:36,023
Our Universe, at large,

601
00:41:36,025 --> 00:41:38,559
has hundreds of billions
of galaxies,

602
00:41:38,561 --> 00:41:42,129
each of which is
more or less like our Milky Way.

603
00:41:42,131 --> 00:41:44,165
So, the number
of planets in our Universe

604
00:41:44,167 --> 00:41:46,033
is virtually uncountable.

605
00:41:46,035 --> 00:41:51,272
Alien earths must be everywhere.

606
00:41:51,274 --> 00:41:54,241
Now, we haven't discovered
even one of them yet.

607
00:41:54,243 --> 00:41:57,811
But statistically speaking,
it is a rock-solid certainty.

608
00:41:57,813 --> 00:42:01,448
There are millions of billions
of planets like the Earth

609
00:42:01,450 --> 00:42:03,784
out there.

610
00:42:03,786 --> 00:42:07,087
And with
that many earth-like planets,

611
00:42:07,089 --> 00:42:11,692
surely, some of them will have
intelligent life.

612
00:42:11,694 --> 00:42:13,394
I would bet everything.

613
00:42:13,396 --> 00:42:14,728
I would bet my house

614
00:42:14,730 --> 00:42:17,798
that there is another Earth
out there somewhere.

615
00:42:17,800 --> 00:42:22,836
There really can be no doubt
that, elsewhere in our Universe,

616
00:42:22,838 --> 00:42:26,373
there are other smart critters
who are asking themselves,

617
00:42:26,375 --> 00:42:29,810
"Gee, I wonder if there are
any other intelligent species

618
00:42:29,812 --> 00:42:31,478
out there in the Universe?"

619
00:42:34,487 --> 00:42:37,767
The story of
the birth of our planet

620
00:42:37,792 --> 00:42:42,298
reveals that we cannot possibly
be alone in the Universe.

621
00:42:44,124 --> 00:42:47,297
The question is not
"Are we alone?",

622
00:42:47,322 --> 00:42:51,187
"it's how far away
are our neighbors?"

623
00:42:51,653 --> 00:42:54,798
"And when will we meet?"

624
00:42:54,799 --> 00:42:58,799
== sync, corrected by elderman ==

625
00:42:58,849 --> 00:43:03,399
Repair and Synchronization by
Easy Subtitles Synchronizer 1.0.0.0