Journey of the Universe Page #3

and of you know, our brains, our skin,

all of it passed through an

intense explosion of a star.

In pondering the source of the Sun's power,

we can now reflect on something

no earlier humans could know.

The Sun is converting four millions tons

of its mass into energy every second.

All of life feeds on the

roaring energy of the Sun.

Our solar system then is a self-energizing

womb of creativity.

And all of this had its

start in a cloud of dust.

It was really difficult

for humans to realize

that we live on a planet circling a star.

I mean we were here for

hundreds of thousands of years

before Aristarchus, 2,000 years ago,

right here on Samos

realized we are spinning

around the Sun.

That was such an amazing insight

that it vanished actually.

And it wasn't until Copernicus

discovered it again

in the 16th century that humans really

began to absorb the fact that we are

on this planet.

Let me use these vegetables

to explain our solar system.

So here we have the Sun,

this cabbage as the Sun.

Now actually, if this were to be in scale,

this cabbage would have

to be a million times

the size of this pepper.

Budgetary considerations

made that impossible.

So you just have to use your imagination.

Now what we've learned in the 20th century

is about the composition of the planets.

First we have the large planets.

So we have Jupiter here,

and we have Saturn and Uranus, and Neptune.

These are large enough to hold on

to all the lighter elements so that

they actually are gaseous.

Too small to be a star,

but yet too large to be solid.

The other kind then, we have indicated here

with these rocks.

So we have Mercury.

Then we have Venus.

Jump over to Mars.

These are the rocky planets,

most of which are solid.

But there's one special rocky planet.

One that's not too small and not too big.

One that's not too hot and not too cold.

One that's not exactly solid,

but not exactly liquid.

We call it home.

Earth is very much like an egg.

The core of the Earth is like the yolk.

The mantle of the Earth

is like the egg white.

And the crust of the Earth

is like like the eggshell.

What happens is that early on

when the Earth is in a molten state,

all of the really heavy

elements like iron and nickel

sink into the core.

And then the elements like magnesium

form this outer layer around

the core, the mantle.

The crust is only 10 to 50 miles thick,

and that's the only solid part of Earth.

All the rest is in motion.

Plumes of molten rock will

rise up from the mantle

and harden into plates that form the crust.

As these plates slide around

the surface of Earth,

they collide and crumple into

majestic mountain ranges.

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