1
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I have a slight problem,
but the show's going on.

2
00:00:26,390 --> 00:00:28,096
My blood's red.

3
00:00:28,706 --> 00:00:30,553
Is Viennese blood red?

4
00:00:30,893 --> 00:00:32,281
(Laughter)

5
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I suspect it is.

6
00:00:36,742 --> 00:00:38,579
Why is blood red?

7
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Does anybody know? Can you tell me?

8
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(Audience) It's iron.

9
00:00:43,890 --> 00:00:45,932
It's iron, yes.

10
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It's iron in the hemoglobin,
in our bloodstream,

11
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that makes the blood red.

12
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Iron is one of the chemical elements,

13
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and I'm going to talk
about that in a moment.

14
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But, just first ...

15
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(Laughter)

16
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... tomato ketchup.

17
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We'll hear more about tomatoes later.

18
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(Laughter) (Applause)

19
00:01:12,720 --> 00:01:16,182
Back to the chemical elements and iron.

20
00:01:16,592 --> 00:01:19,321
It is, indeed, 
one of the chemical elements,

21
00:01:19,321 --> 00:01:23,140
and even if you're not a chemist,
you probably know of some others.

22
00:01:25,950 --> 00:01:29,206
An answer given by a student in an exam.

23
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[H2O is hot water and CO2 is cold water.]

24
00:01:32,131 --> 00:01:34,412
(Laughter)

25
00:01:38,605 --> 00:01:41,444
So, you know what H2O is?

26
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(Audience) Water.
Jocelyn Burnell: Water. CO2?

27
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(Audience) Carbon dioxide.
JB: Carbon dioxide.

28
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So, we've got here
another three chemical elements:

29
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hydrogen, oxygen, and carbon.

30
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And while we're dealing
with student exam questions,

31
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here's another one about water:

32
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Water is composed of two gins ...

33
00:02:02,237 --> 00:02:04,727
[Water is composed of two gins,
Oxygin and Hydrogin.]

34
00:02:04,727 --> 00:02:07,212
[Oxygin is pure gin.
Hydrogin is water and gin.]

35
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(Laughter)

36
00:02:14,723 --> 00:02:19,213
These answers come from
the United States of America, but ...

37
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(Laughter) (Applause)

38
00:02:26,264 --> 00:02:30,561
It's a wonderful resource of all sorts
of amazing things that come true.

39
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Maybe some of you
recall seeing a diagram like this

40
00:02:36,441 --> 00:02:38,933
in school chemistry laboratories.

41
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You can see it in other places, too,

42
00:02:41,771 --> 00:02:46,636
even these days on tea towels,
mugs, bags, pens.

43
00:02:47,716 --> 00:02:53,233
It's a tabulation of the 100 plus
chemical elements that we know about.

44
00:02:55,093 --> 00:02:57,633
In Oxford, where I come from,

45
00:02:58,133 --> 00:03:00,954
we have it on taxis and buses, as well -

46
00:03:00,954 --> 00:03:02,769
but that's Oxford.

47
00:03:02,769 --> 00:03:04,604
(Laughter)

48
00:03:06,243 --> 00:03:10,570
Now, in our bodies, there's clearly
iron in the bloodstream,

49
00:03:10,570 --> 00:03:15,581
there's also hydrogen and oxygen
because we're two-thirds water.

50
00:03:15,961 --> 00:03:19,971
There's carbon in our tissues,
calcium in our bones.

51
00:03:22,781 --> 00:03:26,243
I'm going to focus on the iron
because this is a short talk.

52
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Where did that iron, and, indeed,
where did those other things come from?

53
00:03:32,382 --> 00:03:34,721
How did it get into our bodies?

54
00:03:35,151 --> 00:03:37,435
It's not in the air ... much.

55
00:03:38,545 --> 00:03:42,454
It's come through what we've eaten:
plants and animals.

56
00:03:44,014 --> 00:03:48,083
How did the iron
get into the plants and animals?

57
00:03:49,533 --> 00:03:51,354
Well, it came from the earth.

58
00:03:51,814 --> 00:03:53,668
How did it get into the earth?

59
00:03:53,668 --> 00:03:56,036
Where did it come from before that?

60
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What I am going to be telling you about

61
00:03:59,889 --> 00:04:04,234
is how the stars have created
the chemical elements -

62
00:04:04,234 --> 00:04:09,612
the key ingredients of life:
oxygen, carbon, calcium, iron -

63
00:04:10,102 --> 00:04:12,305
with particular emphasis on the iron.

64
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Stars are formed in some
of the dark spots of the galaxy,

65
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the dark patches.

66
00:04:20,380 --> 00:04:23,603
There are particles
of gas and dust milling around,

67
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by chance as a little knot,

68
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it's got extra gravity,
pulls in some more,

69
00:04:28,444 --> 00:04:30,989
puts up the gravity, pulls in more.

70
00:04:30,989 --> 00:04:33,621
And over some millions of years,

71
00:04:33,621 --> 00:04:38,723
this little knot grows into
what's going to be a full-blown star.

72
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When the temperature
in the middle of this lump

73
00:04:43,455 --> 00:04:46,103
reaches about 10 million degrees,

74
00:04:46,103 --> 00:04:48,377
nuclear reactions start,

75
00:04:48,377 --> 00:04:53,948
and, in particular, a nuclear reaction
of hydrogen being converted to helium.

76
00:04:54,718 --> 00:04:58,349
And there's some energy to spare,
and it comes out of starlight.

77
00:04:59,919 --> 00:05:02,067
Our sun's busy doing that:

78
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our sun is burning about 600 million
tons of hydrogen every second.

79
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It's done that for 5 billion years.

80
00:05:11,382 --> 00:05:15,047
It'll do it for about
another 5 billion years.

81
00:05:15,697 --> 00:05:21,541
And shortly after that, it will end,
and it's actually no use for this story.

82
00:05:21,541 --> 00:05:23,576
(Laughter)

83
00:05:23,576 --> 00:05:27,153
We have to focus
on a very small minority of stars,

84
00:05:27,153 --> 00:05:29,293
the extremely massive ones,

85
00:05:29,293 --> 00:05:33,345
10, 20, 30 times the size of our sun.

86
00:05:34,435 --> 00:05:36,709
Examples of these that you might know:

87
00:05:36,709 --> 00:05:42,517
the Pleiades - which is in the winter sky
near the constellation of Orion,

88
00:05:42,517 --> 00:05:43,731
and Betelgeuse -

89
00:05:43,731 --> 00:05:48,774
which is the reddish star,
top left in the constellation of Orion.

90
00:05:49,904 --> 00:05:53,936
These big stars not only convert
hydrogen to helium,

91
00:05:53,936 --> 00:05:55,443
but then the helium to carbon,

92
00:05:55,443 --> 00:05:59,509
and work their way
across the periodic table

93
00:05:59,509 --> 00:06:02,812
till they end up with iron
in the center of the core.

94
00:06:03,362 --> 00:06:07,630
And this is the first place
that we have iron in the universe -

95
00:06:08,070 --> 00:06:10,054
in the cores of some stars.

96
00:06:11,664 --> 00:06:16,261
Not very useful to us
if it's in the cores of stars.

97
00:06:17,591 --> 00:06:23,512
But star death, dramatic star death,
comes to the rescue.

98
00:06:25,482 --> 00:06:30,430
A pair of photographs here:
a "before" and an "after."

99
00:06:31,220 --> 00:06:34,877
We're looking at
a southern hemisphere object

100
00:06:34,877 --> 00:06:37,614
called the Large Magellanic Cloud.

101
00:06:38,034 --> 00:06:42,196
It's a small galaxy,
external to ours, but quite nearby.

102
00:06:42,726 --> 00:06:46,317
We're seeing up top left
a glowing mass of gas,

103
00:06:47,227 --> 00:06:49,260
quite a lot of pink hydrogen gas,

104
00:06:49,760 --> 00:06:51,898
millions of little stars,

105
00:06:52,348 --> 00:06:55,627
and one of them, bottom right,
picked out with an arrow.

106
00:06:57,147 --> 00:06:59,958
For those of you
who are not astrophysicists,

107
00:07:00,388 --> 00:07:03,478
the arrow's added after the photo's taken.

108
00:07:03,478 --> 00:07:05,720
(Laughter)

109
00:07:07,738 --> 00:07:13,536
But, this inconspicuous star
that we had to pick out with an arrow

110
00:07:13,536 --> 00:07:14,878
becomes this,

111
00:07:15,768 --> 00:07:19,810
and you don't need an arrow
to see that thing in the bottom right.

112
00:07:20,870 --> 00:07:24,354
The star has exploded catastrophically.

113
00:07:24,934 --> 00:07:26,999
It was one of these big stars

114
00:07:26,999 --> 00:07:30,175
like the ones in the Pleiades,
or Betelgeuse.

115
00:07:30,175 --> 00:07:34,177
It's gone all the way through
the various chemical elements.

116
00:07:34,177 --> 00:07:37,757
It's got this range of onion shells
with iron in the middle

117
00:07:37,757 --> 00:07:40,359
and the other chemical
elements outside it,

118
00:07:41,119 --> 00:07:43,237
and it has exploded.

119
00:07:44,487 --> 00:07:47,986
The physics of the explosion
is quite complicated,

120
00:07:47,986 --> 00:07:50,388
so I'm not going to go
into the details of that,

121
00:07:50,388 --> 00:07:52,971
but it is a catastrophic explosion.

122
00:07:53,871 --> 00:07:56,658
We used to assume
it was totally catastrophic.

123
00:07:56,658 --> 00:08:01,047
We now know that the pulsars
that Vlad mentioned in his introduction

124
00:08:01,047 --> 00:08:04,569
are formed from the cores
of these exploding stars.

125
00:08:04,569 --> 00:08:10,016
But 95% of the star
is skooshed out into space,

126
00:08:11,376 --> 00:08:14,895
which means that being
fanned out across space

127
00:08:15,445 --> 00:08:19,618
are useful chemical elements
that were inside the star:

128
00:08:19,618 --> 00:08:23,724
oxygen, calcium, carbon, iron,

129
00:08:24,614 --> 00:08:30,272
spread out, made available
by the catastrophic terminal explosion

130
00:08:30,272 --> 00:08:32,218
of this particular star.

131
00:08:35,168 --> 00:08:41,388
Now, getting from there to us
is quite a long story,

132
00:08:41,928 --> 00:08:44,628
and I'm going to do this bit by mime.

133
00:08:45,908 --> 00:08:48,289
You've probably got some sense

134
00:08:48,289 --> 00:08:52,238
that physics professors
have a slightly dubious reputation.

135
00:08:52,238 --> 00:08:53,190
(Laughter)

136
00:08:53,190 --> 00:08:56,326
The female ones are utterly nuts!

137
00:08:56,759 --> 00:08:58,847
And I'm just about to prove it!

138
00:08:58,847 --> 00:09:00,771
(Applause)

139
00:09:05,317 --> 00:09:07,805
So, this stage is the Milky Way -

140
00:09:07,805 --> 00:09:09,174
our galaxy,

141
00:09:09,614 --> 00:09:13,582
and this is a story
that involves all the Milky Way.

142
00:09:15,002 --> 00:09:18,777
Over here in the Milky Way
is one of these dark clouds

143
00:09:18,777 --> 00:09:21,230
where stars sometimes form,

144
00:09:21,800 --> 00:09:25,698
particles of gas, molecules,
dust milling around.

145
00:09:27,148 --> 00:09:29,241
By chance, there's a little knot,

146
00:09:29,241 --> 00:09:34,159
it has extra gravity, it pulls in
some more bits of dust and gas,

147
00:09:34,159 --> 00:09:36,450
puts up the mass, puts up the gravity,

148
00:09:36,450 --> 00:09:38,291
pulls in some more bits.

149
00:09:39,591 --> 00:09:44,078
To save time, folks, this is going to be
one of these very massive stars,

150
00:09:44,078 --> 00:09:46,949
otherwise we're here for a long time.

151
00:09:47,989 --> 00:09:51,259
So, this gradually grows, gradually grows.

152
00:09:52,259 --> 00:09:54,720
And at the point when it's grown so much

153
00:09:54,720 --> 00:09:59,268
that the temperature in the middle
has reached about 10 million degrees,

154
00:09:59,268 --> 00:10:02,576
it starts its sequence
of nuclear reactions,

155
00:10:03,026 --> 00:10:07,114
and it burns, converts hydrogen to helium.

156
00:10:07,114 --> 00:10:08,797
Brrrr!

157
00:10:10,177 --> 00:10:13,319
Then it starts to run out
of hydrogen in its core.

158
00:10:13,959 --> 00:10:16,467
So it starts converting helium to carbon.

159
00:10:16,467 --> 00:10:17,468
Brrrr!

160
00:10:18,568 --> 00:10:20,219
That doesn't last as long.

161
00:10:20,219 --> 00:10:22,267
Then it runs out of helium in its core,

162
00:10:22,267 --> 00:10:26,226
so it converts carbon
to oxygen, oxygen ...

163
00:10:26,226 --> 00:10:28,409
Brrr! Brr! Brr! Brr!

164
00:10:28,409 --> 00:10:29,709
Boom!

165
00:10:29,709 --> 00:10:31,866
(Laughter)

166
00:10:32,706 --> 00:10:38,116
And millions and millions
and millions of tons of stuff, gas,

167
00:10:38,116 --> 00:10:41,364
fan out from this explosion site

168
00:10:42,204 --> 00:10:44,126
in one part of our Milky Way.

169
00:10:46,616 --> 00:10:49,153
It percolates, slowly,

170
00:10:49,153 --> 00:10:52,600
but we've got eons, there's no rush.

171
00:10:52,600 --> 00:10:54,144
(Laughter)

172
00:10:54,144 --> 00:10:55,720
It can travel,

173
00:10:55,720 --> 00:10:59,026
and it does travel,
gradually, in all directions,

174
00:10:59,026 --> 00:11:01,015
but we're interested in this bit.

175
00:11:02,335 --> 00:11:04,219
And some comes over here

176
00:11:05,039 --> 00:11:07,584
to where there is another
of these dark clouds

177
00:11:07,584 --> 00:11:10,476
with particles of gas
and dust milling around.

178
00:11:11,246 --> 00:11:15,051
And some of the material
from that distant explosion

179
00:11:15,051 --> 00:11:16,816
finds its way over here,

180
00:11:17,216 --> 00:11:21,739
and that material is rich
in carbon and calcium

181
00:11:21,739 --> 00:11:24,478
and iron and oxygen, and so on.

182
00:11:24,478 --> 00:11:26,417
So it joins this cloud,

183
00:11:26,417 --> 00:11:30,165
and by chance a little knot forms,
it's got extra gravity,

184
00:11:30,165 --> 00:11:34,117
pulls in some more particles,
puts up the mass, puts up the gravity,

185
00:11:34,117 --> 00:11:35,831
pulls in some more particles,

186
00:11:35,831 --> 00:11:38,347
puts up the mass, puts up the gravity,

187
00:11:38,347 --> 00:11:41,169
and over a million years,
10 million years,

188
00:11:41,169 --> 00:11:43,050
it grows and grows and grows.

189
00:11:44,030 --> 00:11:47,070
And once again,
I have to crave your indulgence,

190
00:11:47,070 --> 00:11:50,227
could this also be
one of these big stars?--

191
00:11:50,737 --> 00:11:52,977
otherwise we're here all night.

192
00:11:53,717 --> 00:11:56,030
So this big star grows,

193
00:11:56,030 --> 00:12:01,099
and the nuclear reactions start,
and it burns, converts hydrogen to helium.

194
00:12:01,099 --> 00:12:02,199
Brrrr!

195
00:12:02,669 --> 00:12:05,033
Runs out of hydrogen, burns helium. Brrrr!

196
00:12:05,033 --> 00:12:06,620
Runs out of helium, burns carbon.

197
00:12:06,620 --> 00:12:08,965
Brrr! Brr! Brr! Brr! Boom!

198
00:12:08,965 --> 00:12:10,390
(Laughter)

199
00:12:10,390 --> 00:12:12,595
Now, you know the next bit of the story.

200
00:12:12,595 --> 00:12:17,077
Millions and millions and millions
of tons of stuff fan out across space,

201
00:12:17,807 --> 00:12:20,987
and some of it makes its way over here

202
00:12:21,667 --> 00:12:25,696
to another dark part
of the galaxy - the Milky Way -

203
00:12:26,596 --> 00:12:29,651
where there's a star beginning to form.

204
00:12:30,261 --> 00:12:32,651
The material that comes from there

205
00:12:33,191 --> 00:12:38,081
is doubly enriched in carbon
and calcium and iron, and so on,

206
00:12:38,081 --> 00:12:40,859
because of the stuff
that that star generated,

207
00:12:40,859 --> 00:12:43,430
plus the stuff it got
from that star, as well.

208
00:12:44,190 --> 00:12:49,018
So, what's arriving here
is double dose carbon,

209
00:12:49,018 --> 00:12:51,117
calcium, iron, and so on.

210
00:12:51,647 --> 00:12:57,304
And here in this cloud,
a star called the Sun is forming,

211
00:12:57,804 --> 00:12:59,143
and it's made from the stuff

212
00:12:59,143 --> 00:13:01,473
that happens to be
in this patch of the galaxy,

213
00:13:01,473 --> 00:13:03,933
plus the stuff that's come from that star,

214
00:13:03,933 --> 00:13:06,323
plus the stuff
that's come direct from there,

215
00:13:06,323 --> 00:13:09,223
and maybe from some other
exploding stars, as well.

216
00:13:09,723 --> 00:13:13,073
Our sun is a third-generation star.

217
00:13:13,603 --> 00:13:16,673
Our star is a late-forming star,

218
00:13:17,203 --> 00:13:19,192
and it has to be

219
00:13:19,722 --> 00:13:21,404
or we wouldn't be here.

220
00:13:22,424 --> 00:13:28,154
We can only exist close to a young star

221
00:13:28,154 --> 00:13:31,825
that's been enriched
by previous solar cycles.

222
00:13:33,015 --> 00:13:34,678
So, the sun forms,

223
00:13:35,048 --> 00:13:37,305
some of the material is left over.

224
00:13:38,755 --> 00:13:41,341
You've perhaps seen pictures 
of the planet Saturn

225
00:13:41,341 --> 00:13:43,342
with its rings around it.

226
00:13:43,342 --> 00:13:45,402
This is a giant version of that.

227
00:13:45,992 --> 00:13:47,621
So you've got a sun

228
00:13:48,091 --> 00:13:51,188
and some of the debris
in a giant ring around it.

229
00:13:52,428 --> 00:13:54,083
Let's focus on the debris -

230
00:13:54,643 --> 00:13:56,332
little bits going around.

231
00:13:56,332 --> 00:13:59,043
Little bits occasionally collide
with other bits,

232
00:13:59,043 --> 00:14:02,134
and they go around
and collide with other bits

233
00:14:02,134 --> 00:14:03,893
and go around.

234
00:14:03,893 --> 00:14:07,723
And ultimately, you end up with planets

235
00:14:08,353 --> 00:14:11,051
and the ring, the rest
of the ring has disappeared.

236
00:14:11,641 --> 00:14:14,581
The planets are made
of the same stuff as the sun,

237
00:14:14,581 --> 00:14:17,205
which, you remember,
is made of the stuff that was here,

238
00:14:17,205 --> 00:14:19,316
plus stuff from there,
plus stuff from there.

239
00:14:21,756 --> 00:14:23,533
It makes eight planets,

240
00:14:24,183 --> 00:14:26,062
not Pluto.

241
00:14:26,062 --> 00:14:28,063
(Laughter)

242
00:14:28,903 --> 00:14:31,115
Pluto was grabbed later.

243
00:14:31,615 --> 00:14:35,095
You can think of Pluto
as an adopted child, if you wish.

244
00:14:35,605 --> 00:14:37,461
The rest are birth children.

245
00:14:38,801 --> 00:14:43,092
So, these planets are basically
made of the same stuff as the sun,

246
00:14:44,042 --> 00:14:47,064
which is made up of stuff that was here,

247
00:14:47,064 --> 00:14:52,602
plus debris from exploding stars
actually all over our galaxy.

248
00:14:52,602 --> 00:14:55,273
It's not that we can say,
"It was that one and that one."

249
00:14:55,273 --> 00:14:57,696
It's that one and that one
and that one and that one

250
00:14:57,696 --> 00:15:00,192
and that one and that one
and that one and that one -

251
00:15:00,612 --> 00:15:03,775
doubly enriched with all
these useful chemical elements.

252
00:15:04,395 --> 00:15:07,524
And the planets, likewise,
are of the same stuff.

253
00:15:08,284 --> 00:15:09,575
There has been some change

254
00:15:09,575 --> 00:15:12,762
in that the planets
closest to the sun got hot,

255
00:15:12,762 --> 00:15:16,567
and the material that most easily
evaporates has boiled off.

256
00:15:17,147 --> 00:15:20,855
Further out, you can see
the original composition rather better.

257
00:15:21,635 --> 00:15:24,103
But that's broadly what has happened.

258
00:15:24,783 --> 00:15:30,935
So we who eat the plants and the animals
that absorb elements from the earth,

259
00:15:31,765 --> 00:15:34,585
we are made
of the same stuff as the earth,

260
00:15:35,115 --> 00:15:37,664
and the earth is made
of the same stuff as the sun,

261
00:15:38,464 --> 00:15:41,523
which is made up
of the rest of the galaxy.

262
00:15:42,823 --> 00:15:48,164
So, iron was created
in those very massive stars,

263
00:15:48,164 --> 00:15:52,144
ones that went through
lots of nuclear reactions.

264
00:15:53,114 --> 00:15:55,435
And that iron was made available

265
00:15:55,435 --> 00:15:59,357
by the catastrophic death
of those big stars.

266
00:15:59,857 --> 00:16:02,415
So there's life and death already.

267
00:16:04,175 --> 00:16:07,692
If it wasn't for those stars,
particularly the ones that had died,

268
00:16:07,692 --> 00:16:09,543
we would not be here.

269
00:16:10,633 --> 00:16:14,245
And we're intimately and ultimately

270
00:16:14,245 --> 00:16:15,863
children of the stars,

271
00:16:16,753 --> 00:16:19,623
to such an extent that, actually,

272
00:16:19,983 --> 00:16:22,143
we are stars.

273
00:16:22,853 --> 00:16:24,263
Thank you.

274
00:16:24,263 --> 00:16:26,605
(Applause)