WEBVTT

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

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My blood's red.

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Is Viennese blood red?

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(Laughter)

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I suspect it is.

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Why is blood red?

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Does anybody know? Can you tell me?

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(Audience) It's iron.

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It's iron, yes.

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

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that makes the blood red.

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Iron is one of the chemical elements,

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

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But, just first ...

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(Laughter)

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... tomato ketchup.

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We'll hear more about tomatoes later.

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(Laughter) (Applause)

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Back to the chemical elements and iron.

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It is, indeed, 
one of the chemical elements,

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and even if you're not a chemist,
you probably know of some others.

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An answer given by a student in an exam.

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

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(Laughter)

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So, you know what H2O is?

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

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(Audience) Carbon dioxide.
JB: Carbon dioxide.

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

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hydrogen, oxygen, and carbon.

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And while we're dealing
with student exam questions,

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here's another one about water:

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Water is composed of two gins ...

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[Water is composed of two gins,
Oxygin and Hydrogin.]

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[Oxygin is pure gin.
Hydrogin is water and gin.]

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(Laughter)

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These answers come from
the United States of America, but ...

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(Laughter) (Applause)

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It's a wonderful resource of all sorts
of amazing things that come true.

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Maybe some of you
recall seeing a diagram like this

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in school chemistry laboratories.

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You can see it in other places, too,

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even these days on tea towels,
mugs, bags, pens.

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It's a tabulation of the 100 plus
chemical elements that we know about.

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In Oxford, where I come from,

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we have it on taxis and buses, as well -

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but that's Oxford.

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(Laughter)

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Now, in our bodies, there's clearly
iron in the bloodstream,

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there's also hydrogen and oxygen
because we're two-thirds water.

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There's carbon in our tissues,
calcium in our bones.

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I'm going to focus on the iron
because this is a short talk.

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

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How did it get into our bodies?

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It's not in the air ... much.

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It's come through what we've eaten:
plants and animals.

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How did the iron
get into the plants and animals?

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Well, it came from the earth.

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How did it get into the earth?

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Where did it come from before that?

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What I am going to be telling you about

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is how the stars have created
the chemical elements -

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the key ingredients of life:
oxygen, carbon, calcium, iron -

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with particular emphasis on the iron.

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

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the dark patches.

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There are particles
of gas and dust milling around,

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by chance as a little knot,

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

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puts up the gravity, pulls in more.

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And over some millions of years,

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this little knot grows into
what's going to be a full-blown star.

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When the temperature
in the middle of this lump

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reaches about 10 million degrees,

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nuclear reactions start,

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and, in particular, a nuclear reaction
of hydrogen being converted to helium.

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And there's some energy to spare,
and it comes out of starlight.

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Our sun's busy doing that:

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

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It's done that for 5 billion years.

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It'll do it for about
another 5 billion years.

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And shortly after that, it will end,
and it's actually no use for this story.

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(Laughter)

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We have to focus
on a very small minority of stars,

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the extremely massive ones,

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10, 20, 30 times the size of our sun.

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Examples of these that you might know:

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the Pleiades - which is in the winter sky
near the constellation of Orion,

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and Betelgeuse -

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which is the reddish star,
top left in the constellation of Orion.

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These big stars not only convert
hydrogen to helium,

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but then the helium to carbon,

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and work their way
across the periodic table

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till they end up with iron
in the center of the core.

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And this is the first place
that we have iron in the universe -

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in the cores of some stars.

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Not very useful to us
if it's in the cores of stars.

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But star death, dramatic star death,
comes to the rescue.

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A pair of photographs here:
a "before" and an "after."

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We're looking at
a southern hemisphere object

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called the Large Magellanic Cloud.

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It's a small galaxy,
external to ours, but quite nearby.

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We're seeing up top left
a glowing mass of gas,

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quite a lot of pink hydrogen gas,

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millions of little stars,

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and one of them, bottom right,
picked out with an arrow.

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For those of you
who are not astrophysicists,

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the arrow's added after the photo's taken.

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(Laughter)

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But, this inconspicuous star
that we had to pick out with an arrow

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becomes this,

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and you don't need an arrow
to see that thing in the bottom right.

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The star has exploded catastrophically.

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It was one of these big stars

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like the ones in the Pleiades,
or Betelgeuse.

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It's gone all the way through
the various chemical elements.

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It's got this range of onion shells
with iron in the middle

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and the other chemical
elements outside it,

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and it has exploded.

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The physics of the explosion
is quite complicated,

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so I'm not going to go
into the details of that,

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but it is a catastrophic explosion.

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We used to assume
it was totally catastrophic.

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We now know that the pulsars
that Vlad mentioned in his introduction

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are formed from the cores
of these exploding stars.

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But 95% of the star
is skooshed out into space,

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which means that being
fanned out across space

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are useful chemical elements
that were inside the star:

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oxygen, calcium, carbon, iron,

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spread out, made available
by the catastrophic terminal explosion

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of this particular star.

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Now, getting from there to us
is quite a long story,

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and I'm going to do this bit by mime.

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You've probably got some sense

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that physics professors
have a slightly dubious reputation.

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(Laughter)

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The female ones are utterly nuts!

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And I'm just about to prove it!

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(Applause)

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So, this stage is the Milky Way -

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our galaxy,

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and this is a story
that involves all the Milky Way.

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Over here in the Milky Way
is one of these dark clouds

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where stars sometimes form,

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particles of gas, molecules,
dust milling around.

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By chance, there's a little knot,

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it has extra gravity, it pulls in
some more bits of dust and gas,

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puts up the mass, puts up the gravity,

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pulls in some more bits.

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To save time, folks, this is going to be
one of these very massive stars,

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otherwise we're here for a long time.

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So, this gradually grows, gradually grows.

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And at the point when it's grown so much

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that the temperature in the middle
has reached about 10 million degrees,

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it starts its sequence
of nuclear reactions,

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and it burns, converts hydrogen to helium.

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Brrrr!

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Then it starts to run out
of hydrogen in its core.

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So it starts converting helium to carbon.

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Brrrr!

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That doesn't last as long.

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Then it runs out of helium in its core,

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so it converts carbon
to oxygen, oxygen ...

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Brrr! Brr! Brr! Brr!

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Boom!

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(Laughter)

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And millions and millions
and millions of tons of stuff, gas,

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fan out from this explosion site

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in one part of our Milky Way.

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It percolates, slowly,

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but we've got eons, there's no rush.

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(Laughter)

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It can travel,

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and it does travel,
gradually, in all directions,

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but we're interested in this bit.

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And some comes over here

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to where there is another
of these dark clouds

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with particles of gas
and dust milling around.

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And some of the material
from that distant explosion

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finds its way over here,

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and that material is rich
in carbon and calcium

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and iron and oxygen, and so on.

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So it joins this cloud,

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and by chance a little knot forms,
it's got extra gravity,

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pulls in some more particles,
puts up the mass, puts up the gravity,

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pulls in some more particles,

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puts up the mass, puts up the gravity,

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and over a million years,
10 million years,

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it grows and grows and grows.

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And once again,
I have to crave your indulgence,

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could this also be
one of these big stars?--

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otherwise we're here all night.

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So this big star grows,

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and the nuclear reactions start,
and it burns, converts hydrogen to helium.

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Brrrr!

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Runs out of hydrogen, burns helium. Brrrr!

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Runs out of helium, burns carbon.

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Brrr! Brr! Brr! Brr! Boom!

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(Laughter)

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Now, you know the next bit of the story.

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Millions and millions and millions
of tons of stuff fan out across space,

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and some of it makes its way over here

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to another dark part
of the galaxy - the Milky Way -

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where there's a star beginning to form.

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The material that comes from there

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is doubly enriched in carbon
and calcium and iron, and so on,

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because of the stuff
that that star generated,

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plus the stuff it got
from that star, as well.

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So, what's arriving here
is double dose carbon,

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calcium, iron, and so on.

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And here in this cloud,
a star called the Sun is forming,

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and it's made from the stuff

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that happens to be
in this patch of the galaxy,

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plus the stuff that's come from that star,

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plus the stuff
that's come direct from there,

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and maybe from some other
exploding stars, as well.

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Our sun is a third-generation star.

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Our star is a late-forming star,

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and it has to be

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or we wouldn't be here.

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We can only exist close to a young star

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that's been enriched
by previous solar cycles.

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So, the sun forms,

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some of the material is left over.

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You've perhaps seen pictures 
of the planet Saturn

00:13:41.341 --> 00:13:43.342
with its rings around it.

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This is a giant version of that.

00:13:45.992 --> 00:13:47.621
So you've got a sun

00:13:48.091 --> 00:13:51.188
and some of the debris
in a giant ring around it.

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Let's focus on the debris -

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little bits going around.

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Little bits occasionally collide
with other bits,

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and they go around
and collide with other bits

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and go around.

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And ultimately, you end up with planets

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and the ring, the rest
of the ring has disappeared.

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The planets are made
of the same stuff as the sun,

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which, you remember,
is made of the stuff that was here,

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plus stuff from there,
plus stuff from there.

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It makes eight planets,

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not Pluto.

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(Laughter)

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Pluto was grabbed later.

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You can think of Pluto
as an adopted child, if you wish.

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The rest are birth children.

00:14:38.801 --> 00:14:43.092
So, these planets are basically
made of the same stuff as the sun,

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which is made up of stuff that was here,

00:14:47.064 --> 00:14:52.602
plus debris from exploding stars
actually all over our galaxy.

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It's not that we can say,
"It was that one and that one."

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It's that one and that one
and that one and that one

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and that one and that one
and that one and that one -

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doubly enriched with all
these useful chemical elements.

00:15:04.395 --> 00:15:07.524
And the planets, likewise,
are of the same stuff.

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There has been some change

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in that the planets
closest to the sun got hot,

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and the material that most easily
evaporates has boiled off.

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Further out, you can see
the original composition rather better.

00:15:21.635 --> 00:15:24.103
But that's broadly what has happened.

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So we who eat the plants and the animals
that absorb elements from the earth,

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we are made
of the same stuff as the earth,

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and the earth is made
of the same stuff as the sun,

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which is made up
of the rest of the galaxy.

00:15:42.823 --> 00:15:48.164
So, iron was created
in those very massive stars,

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ones that went through
lots of nuclear reactions.

00:15:53.114 --> 00:15:55.435
And that iron was made available

00:15:55.435 --> 00:15:59.357
by the catastrophic death
of those big stars.

00:15:59.857 --> 00:16:02.415
So there's life and death already.

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If it wasn't for those stars,
particularly the ones that had died,

00:16:07.692 --> 00:16:09.543
we would not be here.

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And we're intimately and ultimately

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children of the stars,

00:16:16.753 --> 00:16:19.623
to such an extent that, actually,

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we are stars.

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Thank you.

00:16:24.263 --> 00:16:26.605
(Applause)