0:00:19.396,0:00:23.690
I have a slight problem,[br]but the show's going on.

0:00:26.390,0:00:28.096
My blood's red.

0:00:28.706,0:00:30.553
Is Viennese blood red?

0:00:30.893,0:00:32.281
(Laughter)

0:00:32.281,0:00:33.892
I suspect it is.

0:00:36.742,0:00:38.579
Why is blood red?

0:00:40.342,0:00:42.841
Does anybody know? Can you tell me?

0:00:42.841,0:00:43.890
(Audience) It's iron.

0:00:43.890,0:00:45.932
It's iron, yes.

0:00:45.932,0:00:49.460
It's iron in the hemoglobin,[br]in our bloodstream,

0:00:49.880,0:00:51.640
that makes the blood red.

0:00:52.430,0:00:54.382
Iron is one of the chemical elements,

0:00:54.382,0:00:56.476
and I'm going to talk[br]about that in a moment.

0:00:56.476,0:00:57.661
But, just first ...

0:00:58.401,0:01:00.262
(Laughter)

0:01:00.262,0:01:01.648
... tomato ketchup.

0:01:02.202,0:01:04.674
We'll hear more about tomatoes later.

0:01:04.674,0:01:07.114
(Laughter) (Applause)

0:01:12.720,0:01:16.182
Back to the chemical elements and iron.

0:01:16.592,0:01:19.321
It is, indeed, [br]one of the chemical elements,

0:01:19.321,0:01:23.140
and even if you're not a chemist,[br]you probably know of some others.

0:01:25.950,0:01:29.206
An answer given by a student in an exam.

0:01:29.206,0:01:32.131
[H2O is hot water and CO2 is cold water.]

0:01:32.131,0:01:34.412
(Laughter)

0:01:38.605,0:01:41.444
So, you know what H2O is?

0:01:42.134,0:01:45.463
(Audience) Water.[br]Jocelyn Burnell: Water. CO2?

0:01:45.463,0:01:47.664
(Audience) Carbon dioxide.[br]JB: Carbon dioxide.

0:01:47.664,0:01:51.233
So, we've got here[br]another three chemical elements:

0:01:51.233,0:01:54.052
hydrogen, oxygen, and carbon.

0:01:54.852,0:01:57.282
And while we're dealing[br]with student exam questions,

0:01:57.282,0:01:59.280
here's another one about water:

0:02:00.000,0:02:02.237
Water is composed of two gins ...

0:02:02.237,0:02:04.727
[Water is composed of two gins,[br]Oxygin and Hydrogin.]

0:02:04.727,0:02:07.212
[Oxygin is pure gin.[br]Hydrogin is water and gin.]

0:02:07.212,0:02:09.167
(Laughter)

0:02:14.723,0:02:19.213
These answers come from[br]the United States of America, but ...

0:02:19.213,0:02:21.993
(Laughter) (Applause)

0:02:26.264,0:02:30.561
It's a wonderful resource of all sorts[br]of amazing things that come true.

0:02:32.975,0:02:36.441
Maybe some of you[br]recall seeing a diagram like this

0:02:36.441,0:02:38.933
in school chemistry laboratories.

0:02:39.493,0:02:41.771
You can see it in other places, too,

0:02:41.771,0:02:46.636
even these days on tea towels,[br]mugs, bags, pens.

0:02:47.716,0:02:53.233
It's a tabulation of the 100 plus[br]chemical elements that we know about.

0:02:55.093,0:02:57.633
In Oxford, where I come from,

0:02:58.133,0:03:00.954
we have it on taxis and buses, as well -

0:03:00.954,0:03:02.769
but that's Oxford.

0:03:02.769,0:03:04.604
(Laughter)

0:03:06.243,0:03:10.570
Now, in our bodies, there's clearly[br]iron in the bloodstream,

0:03:10.570,0:03:15.581
there's also hydrogen and oxygen[br]because we're two-thirds water.

0:03:15.961,0:03:19.971
There's carbon in our tissues,[br]calcium in our bones.

0:03:22.781,0:03:26.243
I'm going to focus on the iron[br]because this is a short talk.

0:03:27.774,0:03:32.382
Where did that iron, and, indeed,[br]where did those other things come from?

0:03:32.382,0:03:34.721
How did it get into our bodies?

0:03:35.151,0:03:37.435
It's not in the air ... much.

0:03:38.545,0:03:42.454
It's come through what we've eaten:[br]plants and animals.

0:03:44.014,0:03:48.083
How did the iron[br]get into the plants and animals?

0:03:49.533,0:03:51.354
Well, it came from the earth.

0:03:51.814,0:03:53.668
How did it get into the earth?

0:03:53.668,0:03:56.036
Where did it come from before that?

0:03:57.976,0:03:59.889
What I am going to be telling you about

0:03:59.889,0:04:04.234
is how the stars have created[br]the chemical elements -

0:04:04.234,0:04:09.612
the key ingredients of life:[br]oxygen, carbon, calcium, iron -

0:04:10.102,0:04:12.305
with particular emphasis on the iron.

0:04:14.075,0:04:18.463
Stars are formed in some[br]of the dark spots of the galaxy,

0:04:18.463,0:04:19.950
the dark patches.

0:04:20.380,0:04:23.603
There are particles[br]of gas and dust milling around,

0:04:23.973,0:04:25.671
by chance as a little knot,

0:04:25.671,0:04:28.444
it's got extra gravity,[br]pulls in some more,

0:04:28.444,0:04:30.989
puts up the gravity, pulls in more.

0:04:30.989,0:04:33.621
And over some millions of years,

0:04:33.621,0:04:38.723
this little knot grows into[br]what's going to be a full-blown star.

0:04:39.833,0:04:43.455
When the temperature[br]in the middle of this lump

0:04:43.455,0:04:46.103
reaches about 10 million degrees,

0:04:46.103,0:04:48.377
nuclear reactions start,

0:04:48.377,0:04:53.948
and, in particular, a nuclear reaction[br]of hydrogen being converted to helium.

0:04:54.718,0:04:58.349
And there's some energy to spare,[br]and it comes out of starlight.

0:04:59.919,0:05:02.067
Our sun's busy doing that:

0:05:02.067,0:05:07.676
our sun is burning about 600 million[br]tons of hydrogen every second.

0:05:08.526,0:05:11.382
It's done that for 5 billion years.

0:05:11.382,0:05:15.047
It'll do it for about[br]another 5 billion years.

0:05:15.697,0:05:21.541
And shortly after that, it will end,[br]and it's actually no use for this story.

0:05:21.541,0:05:23.576
(Laughter)

0:05:23.576,0:05:27.153
We have to focus[br]on a very small minority of stars,

0:05:27.153,0:05:29.293
the extremely massive ones,

0:05:29.293,0:05:33.345
10, 20, 30 times the size of our sun.

0:05:34.435,0:05:36.709
Examples of these that you might know:

0:05:36.709,0:05:42.517
the Pleiades - which is in the winter sky[br]near the constellation of Orion,

0:05:42.517,0:05:43.731
and Betelgeuse -

0:05:43.731,0:05:48.774
which is the reddish star,[br]top left in the constellation of Orion.

0:05:49.904,0:05:53.936
These big stars not only convert[br]hydrogen to helium,

0:05:53.936,0:05:55.443
but then the helium to carbon,

0:05:55.443,0:05:59.509
and work their way[br]across the periodic table

0:05:59.509,0:06:02.812
till they end up with iron[br]in the center of the core.

0:06:03.362,0:06:07.630
And this is the first place[br]that we have iron in the universe -

0:06:08.070,0:06:10.054
in the cores of some stars.

0:06:11.664,0:06:16.261
Not very useful to us[br]if it's in the cores of stars.

0:06:17.591,0:06:23.512
But star death, dramatic star death,[br]comes to the rescue.

0:06:25.482,0:06:30.430
A pair of photographs here:[br]a "before" and an "after."

0:06:31.220,0:06:34.877
We're looking at[br]a southern hemisphere object

0:06:34.877,0:06:37.614
called the Large Magellanic Cloud.

0:06:38.034,0:06:42.196
It's a small galaxy,[br]external to ours, but quite nearby.

0:06:42.726,0:06:46.317
We're seeing up top left[br]a glowing mass of gas,

0:06:47.227,0:06:49.260
quite a lot of pink hydrogen gas,

0:06:49.760,0:06:51.898
millions of little stars,

0:06:52.348,0:06:55.627
and one of them, bottom right,[br]picked out with an arrow.

0:06:57.147,0:06:59.958
For those of you[br]who are not astrophysicists,

0:07:00.388,0:07:03.478
the arrow's added after the photo's taken.

0:07:03.478,0:07:05.720
(Laughter)

0:07:07.738,0:07:13.536
But, this inconspicuous star[br]that we had to pick out with an arrow

0:07:13.536,0:07:14.878
becomes this,

0:07:15.768,0:07:19.810
and you don't need an arrow[br]to see that thing in the bottom right.

0:07:20.870,0:07:24.354
The star has exploded catastrophically.

0:07:24.934,0:07:26.999
It was one of these big stars

0:07:26.999,0:07:30.175
like the ones in the Pleiades,[br]or Betelgeuse.

0:07:30.175,0:07:34.177
It's gone all the way through[br]the various chemical elements.

0:07:34.177,0:07:37.757
It's got this range of onion shells[br]with iron in the middle

0:07:37.757,0:07:40.359
and the other chemical[br]elements outside it,

0:07:41.119,0:07:43.237
and it has exploded.

0:07:44.487,0:07:47.986
The physics of the explosion[br]is quite complicated,

0:07:47.986,0:07:50.388
so I'm not going to go[br]into the details of that,

0:07:50.388,0:07:52.971
but it is a catastrophic explosion.

0:07:53.871,0:07:56.658
We used to assume[br]it was totally catastrophic.

0:07:56.658,0:08:01.047
We now know that the pulsars[br]that Vlad mentioned in his introduction

0:08:01.047,0:08:04.569
are formed from the cores[br]of these exploding stars.

0:08:04.569,0:08:10.016
But 95% of the star[br]is skooshed out into space,

0:08:11.376,0:08:14.895
which means that being[br]fanned out across space

0:08:15.445,0:08:19.618
are useful chemical elements[br]that were inside the star:

0:08:19.618,0:08:23.724
oxygen, calcium, carbon, iron,

0:08:24.614,0:08:30.272
spread out, made available[br]by the catastrophic terminal explosion

0:08:30.272,0:08:32.218
of this particular star.

0:08:35.168,0:08:41.388
Now, getting from there to us[br]is quite a long story,

0:08:41.928,0:08:44.628
and I'm going to do this bit by mime.

0:08:45.908,0:08:48.289
You've probably got some sense

0:08:48.289,0:08:52.238
that physics professors[br]have a slightly dubious reputation.

0:08:52.238,0:08:53.190
(Laughter)

0:08:53.190,0:08:56.326
The female ones are utterly nuts!

0:08:56.759,0:08:58.847
And I'm just about to prove it!

0:08:58.847,0:09:00.771
(Applause)

0:09:05.317,0:09:07.805
So, this stage is the Milky Way -

0:09:07.805,0:09:09.174
our galaxy,

0:09:09.614,0:09:13.582
and this is a story[br]that involves all the Milky Way.

0:09:15.002,0:09:18.777
Over here in the Milky Way[br]is one of these dark clouds

0:09:18.777,0:09:21.230
where stars sometimes form,

0:09:21.800,0:09:25.698
particles of gas, molecules,[br]dust milling around.

0:09:27.148,0:09:29.241
By chance, there's a little knot,

0:09:29.241,0:09:34.159
it has extra gravity, it pulls in[br]some more bits of dust and gas,

0:09:34.159,0:09:36.450
puts up the mass, puts up the gravity,

0:09:36.450,0:09:38.291
pulls in some more bits.

0:09:39.591,0:09:44.078
To save time, folks, this is going to be[br]one of these very massive stars,

0:09:44.078,0:09:46.949
otherwise we're here for a long time.

0:09:47.989,0:09:51.259
So, this gradually grows, gradually grows.

0:09:52.259,0:09:54.720
And at the point when it's grown so much

0:09:54.720,0:09:59.268
that the temperature in the middle[br]has reached about 10 million degrees,

0:09:59.268,0:10:02.576
it starts its sequence[br]of nuclear reactions,

0:10:03.026,0:10:07.114
and it burns, converts hydrogen to helium.

0:10:07.114,0:10:08.797
Brrrr!

0:10:10.177,0:10:13.319
Then it starts to run out[br]of hydrogen in its core.

0:10:13.959,0:10:16.467
So it starts converting helium to carbon.

0:10:16.467,0:10:17.468
Brrrr!

0:10:18.568,0:10:20.219
That doesn't last as long.

0:10:20.219,0:10:22.267
Then it runs out of helium in its core,

0:10:22.267,0:10:26.226
so it converts carbon[br]to oxygen, oxygen ...

0:10:26.226,0:10:28.409
Brrr! Brr! Brr! Brr!

0:10:28.409,0:10:29.709
Boom!

0:10:29.709,0:10:31.866
(Laughter)

0:10:32.706,0:10:38.116
And millions and millions[br]and millions of tons of stuff, gas,

0:10:38.116,0:10:41.364
fan out from this explosion site

0:10:42.204,0:10:44.126
in one part of our Milky Way.

0:10:46.616,0:10:49.153
It percolates, slowly,

0:10:49.153,0:10:52.600
but we've got eons, there's no rush.

0:10:52.600,0:10:54.144
(Laughter)

0:10:54.144,0:10:55.720
It can travel,

0:10:55.720,0:10:59.026
and it does travel,[br]gradually, in all directions,

0:10:59.026,0:11:01.015
but we're interested in this bit.

0:11:02.335,0:11:04.219
And some comes over here

0:11:05.039,0:11:07.584
to where there is another[br]of these dark clouds

0:11:07.584,0:11:10.476
with particles of gas[br]and dust milling around.

0:11:11.246,0:11:15.051
And some of the material[br]from that distant explosion

0:11:15.051,0:11:16.816
finds its way over here,

0:11:17.216,0:11:21.739
and that material is rich[br]in carbon and calcium

0:11:21.739,0:11:24.478
and iron and oxygen, and so on.

0:11:24.478,0:11:26.417
So it joins this cloud,

0:11:26.417,0:11:30.165
and by chance a little knot forms,[br]it's got extra gravity,

0:11:30.165,0:11:34.117
pulls in some more particles,[br]puts up the mass, puts up the gravity,

0:11:34.117,0:11:35.831
pulls in some more particles,

0:11:35.831,0:11:38.347
puts up the mass, puts up the gravity,

0:11:38.347,0:11:41.169
and over a million years,[br]10 million years,

0:11:41.169,0:11:43.050
it grows and grows and grows.

0:11:44.030,0:11:47.070
And once again,[br]I have to crave your indulgence,

0:11:47.070,0:11:50.227
could this also be[br]one of these big stars?--

0:11:50.737,0:11:52.977
otherwise we're here all night.

0:11:53.717,0:11:56.030
So this big star grows,

0:11:56.030,0:12:01.099
and the nuclear reactions start,[br]and it burns, converts hydrogen to helium.

0:12:01.099,0:12:02.199
Brrrr!

0:12:02.669,0:12:05.033
Runs out of hydrogen, burns helium. Brrrr!

0:12:05.033,0:12:06.620
Runs out of helium, burns carbon.

0:12:06.620,0:12:08.965
Brrr! Brr! Brr! Brr! Boom!

0:12:08.965,0:12:10.390
(Laughter)

0:12:10.390,0:12:12.595
Now, you know the next bit of the story.

0:12:12.595,0:12:17.077
Millions and millions and millions[br]of tons of stuff fan out across space,

0:12:17.807,0:12:20.987
and some of it makes its way over here

0:12:21.667,0:12:25.696
to another dark part[br]of the galaxy - the Milky Way -

0:12:26.596,0:12:29.651
where there's a star beginning to form.

0:12:30.261,0:12:32.651
The material that comes from there

0:12:33.191,0:12:38.081
is doubly enriched in carbon[br]and calcium and iron, and so on,

0:12:38.081,0:12:40.859
because of the stuff[br]that that star generated,

0:12:40.859,0:12:43.430
plus the stuff it got[br]from that star, as well.

0:12:44.190,0:12:49.018
So, what's arriving here[br]is double dose carbon,

0:12:49.018,0:12:51.117
calcium, iron, and so on.

0:12:51.647,0:12:57.304
And here in this cloud,[br]a star called the Sun is forming,

0:12:57.804,0:12:59.143
and it's made from the stuff

0:12:59.143,0:13:01.473
that happens to be[br]in this patch of the galaxy,

0:13:01.473,0:13:03.933
plus the stuff that's come from that star,

0:13:03.933,0:13:06.323
plus the stuff[br]that's come direct from there,

0:13:06.323,0:13:09.223
and maybe from some other[br]exploding stars, as well.

0:13:09.723,0:13:13.073
Our sun is a third-generation star.

0:13:13.603,0:13:16.673
Our star is a late-forming star,

0:13:17.203,0:13:19.192
and it has to be

0:13:19.722,0:13:21.404
or we wouldn't be here.

0:13:22.424,0:13:28.154
We can only exist close to a young star

0:13:28.154,0:13:31.825
that's been enriched[br]by previous solar cycles.

0:13:33.015,0:13:34.678
So, the sun forms,

0:13:35.048,0:13:37.305
some of the material is left over.

0:13:38.755,0:13:41.341
You've perhaps seen pictures [br]of the planet Saturn

0:13:41.341,0:13:43.342
with its rings around it.

0:13:43.342,0:13:45.402
This is a giant version of that.

0:13:45.992,0:13:47.621
So you've got a sun

0:13:48.091,0:13:51.188
and some of the debris[br]in a giant ring around it.

0:13:52.428,0:13:54.083
Let's focus on the debris -

0:13:54.643,0:13:56.332
little bits going around.

0:13:56.332,0:13:59.043
Little bits occasionally collide[br]with other bits,

0:13:59.043,0:14:02.134
and they go around[br]and collide with other bits

0:14:02.134,0:14:03.893
and go around.

0:14:03.893,0:14:07.723
And ultimately, you end up with planets

0:14:08.353,0:14:11.051
and the ring, the rest[br]of the ring has disappeared.

0:14:11.641,0:14:14.581
The planets are made[br]of the same stuff as the sun,

0:14:14.581,0:14:17.205
which, you remember,[br]is made of the stuff that was here,

0:14:17.205,0:14:19.316
plus stuff from there,[br]plus stuff from there.

0:14:21.756,0:14:23.533
It makes eight planets,

0:14:24.183,0:14:26.062
not Pluto.

0:14:26.062,0:14:28.063
(Laughter)

0:14:28.903,0:14:31.115
Pluto was grabbed later.

0:14:31.615,0:14:35.095
You can think of Pluto[br]as an adopted child, if you wish.

0:14:35.605,0:14:37.461
The rest are birth children.

0:14:38.801,0:14:43.092
So, these planets are basically[br]made of the same stuff as the sun,

0:14:44.042,0:14:47.064
which is made up of stuff that was here,

0:14:47.064,0:14:52.602
plus debris from exploding stars[br]actually all over our galaxy.

0:14:52.602,0:14:55.273
It's not that we can say,[br]"It was that one and that one."

0:14:55.273,0:14:57.696
It's that one and that one[br]and that one and that one

0:14:57.696,0:15:00.192
and that one and that one[br]and that one and that one -

0:15:00.612,0:15:03.775
doubly enriched with all[br]these useful chemical elements.

0:15:04.395,0:15:07.524
And the planets, likewise,[br]are of the same stuff.

0:15:08.284,0:15:09.575
There has been some change

0:15:09.575,0:15:12.762
in that the planets[br]closest to the sun got hot,

0:15:12.762,0:15:16.567
and the material that most easily[br]evaporates has boiled off.

0:15:17.147,0:15:20.855
Further out, you can see[br]the original composition rather better.

0:15:21.635,0:15:24.103
But that's broadly what has happened.

0:15:24.783,0:15:30.935
So we who eat the plants and the animals[br]that absorb elements from the earth,

0:15:31.765,0:15:34.585
we are made[br]of the same stuff as the earth,

0:15:35.115,0:15:37.664
and the earth is made[br]of the same stuff as the sun,

0:15:38.464,0:15:41.523
which is made up[br]of the rest of the galaxy.

0:15:42.823,0:15:48.164
So, iron was created[br]in those very massive stars,

0:15:48.164,0:15:52.144
ones that went through[br]lots of nuclear reactions.

0:15:53.114,0:15:55.435
And that iron was made available

0:15:55.435,0:15:59.357
by the catastrophic death[br]of those big stars.

0:15:59.857,0:16:02.415
So there's life and death already.

0:16:04.175,0:16:07.692
If it wasn't for those stars,[br]particularly the ones that had died,

0:16:07.692,0:16:09.543
we would not be here.

0:16:10.633,0:16:14.245
And we're intimately and ultimately

0:16:14.245,0:16:15.863
children of the stars,

0:16:16.753,0:16:19.623
to such an extent that, actually,

0:16:19.983,0:16:22.143
we are stars.

0:16:22.853,0:16:24.263
Thank you.

0:16:24.263,0:16:26.605
(Applause)