Today we're going to be talking about the formation

of the solar system,

approximately 4.567 billion years ago.

Four, five, six, seven.

Could that possibly be a coincidence?

Yes.

So if you weren't asleep during like every minute

of grade school, you're probably familiar with the basic layout

of the solar system and the eight-- formerly nine-- planets.

What you may not know is how the planets fit between

the stars and life as the lynchpin of rising complexity.

Mr. Green, Mr. Green, what about Pluto?

Oh, me from the past, I know people like to root

for the underdog, particularly when the underdog shares a name

with Mickey Mouse's dog.

Off-topic, but how come Mickey Mouse has a dog

who is a dog and also a friend, Goofy, who is a dog?

But just remember that Pluto also shares a name

with the Roman god of the underworld,

who was very unlikeable.

But regardless, the word planet is a manmade classification

for a natural phenomenon.

We use it because it makes it easier to do science.

Pluto hasn't cleared the rocks within its neighborhood orbit

like planets usually do, and there's even a dwarf planet

on the edge of our solar system, Eris, that's bigger than Pluto,

and there are hundreds of others that are comparable to Pluto.

The nature of the universe has not changed.

It's just that we learned that Pluto was not acting

like a planet, so can we please just drop the Pluto thing?

# #

So we're now moving from the scale of galaxies,

which involve millions of light years to a neighborhood

that's only a few light hours from the sun to Neptune,

the farthest planet.

Or at most, a light year or two to the distant Oort cloud

of billions of comets held by the gravity of our sun.

So last episode we talked about how the stars are like

our great-great-great many, many times over grandparents.

Well, our sun actually had stars as its parents, too.

It's most likely a second generation star,

which means that the sun was formed from the wreckage

of previous dead stars, and that it contains elements

other than just hydrogen and helium--

heavier elements that are forged in the bellies of stars.

And some of which are like flung out by supernovae.

When our star formed, its immense gravitational pull

sucked in 99.99% of all the matter in the solar system.

So in this case, we are all the 0.01%.

But essentially the rest of the solar system is made up

of the debris, like the crumbs,

the dregs in the bottom of your coffee cup.

Our sun formed over the course of about 100,000 years

in what's called a solar nebula, which is like a fiery cradle

of wisps of dust and gas.

Then the solar nebula began to compress into a star,

probably triggered by a nearby supernova that also, usefully,

peppered the solar system with even more heavy elements.

And then as the sun slurped up like almost all the matter

in the solar system, pressure made the core of the sun

heat up and it came to life.

The usual fusion of hydrogen and helium began to happen,

and continues to happen, which is nice, because otherwise

the Earth would be extremely cold and also very dead.

So how do we know all of this is true?

Well, let's talk to Emily from The Brain Scoop.

Well, a good piece of evidence

is the construction site rubble from that time.

Meteorites form a sort of fossil record.

Meteorites fall to Earth, and some of them

are primitive clumps of nebular dust.

Careful investigation reveals them to be

around 4.568 billion years old.

The point is there can only be two environments where iron-60

came from: one is inside a very old, giant red star,

and the other is within a supernova.

Elderly red giants move away from star-forming regions

in the galaxy.

Chances are, the sun wasn't formed

near one of those, so it's much more likely

that our sun's formation was triggered by a supernova blast.

- So in the early days, the heat from the sun blasted

lots of gassy materials away from the inner regions

of the solar system,

encompassing Mercury, Venus, Earth, and Mars.

Further out in the vicinity of where Jupiter is now,

it was cold enough for volatile gases to hang around,

and even become liquids or solids.

That's why the inner planets like us are rocky,

and the outer planets-- Jupiter, Saturn, Uranus, and Neptune--

are all these humongous gas giants.

So what happened to the remaining 0.01%

of our solar system and what does this have to do

with the rise of complexity?

Well, the dust floating around the baby solar system

wasn't just elements.

Like heating in the stellar nebula allowed this dust

to sometimes form more complex configurations of elements.

Like for one thing, around 60 different kinds of minerals.

So then the dust began to stick together.

Why do I have balloons, by the way?

Well, obviously, I'm going to tell you shortly.

So you may have noticed that if you rub a balloon

onto your head for long enough, it will stick.

That's because of electrostatic forces.

Precisely the same forces that allowed the dust

in the solar system to gently collide and stick together.

And then as those clumps of dust got bigger and bigger,

the collisions ceased to be so gentle.

So within 100,000 years there were many objects

of up to ten kilometers in diameter in the solar system,

and the force and heat of those violent collisions

allowed the formation of still more celestial bodies.

Objects continued to collide, the larger objects

sucking in the smaller ones with their gravitational nets,

and then the largest in each orbit began bulldozing its way

through the remaining material.

So after about a million years, the solar system consisted

of a few dozen or so protoplanets.

They were roughly between the size of Mars and our moon.

And then over the next ten to 100 million years,

the game of pool continued.

Each collision being something terrifying to behold

until we wound up with the eight massive planets

we are familiar with today.

But, of course, there's more than just planets

in our solar system, there's an asteroid belt

between Mars and Jupiter, for instance,

which may be a failed planet messed up

by Jupiter's gigantic gravitational pull.

And then on the edge of the solar system

there's the Kuiper Belt, a region of planetary shrapnel

like poor old Pluto.

And even further out in the boonies,

there is the Oort cloud.

It's like this huge borderland teeming with billions of comets,

but it's still within the sun's gravitational pull.

And the Oort cloud is a light year away.

That's how massive our sun is,

and it's a pretty modest-sized star.

So this was a pretty intense time in terms of

energy transference.

Like all those protoplanets smashing together

converted huge amounts of kinetic energy to heat.

In fact, it was so much heat that when combined

with the heat put off by radioactive materials

in the early solar system,

the earth was a molten ball of lava.

Basically, the entire planet was as hot as Houston, Texas.

What's that?

Apparently it was much hotter than Houston, Texas.

Anyway, the Earth underwent a process of differentiation,

whereby heavy elements sank to the center,

and many lighter elements floated to the surface.

A lot of the metallic elements like iron and nickel

sank through the hot sludge to the core, where they still are.

And the lighter silicates floated upward,

forming the Earth's mantle,

a region about 3,000 kilometers thick.

The even lighter silicates floated to the surface,

where they eventually cooled into the Earth's crust,

about 35 kilometers thick in some places,

and at the bottom of the deepest oceans,

about as thin as seven kilometers.

You can think of the crust as like the thin layer of skin

that forms on a bowl of hot clam chowder

and you wouldn't be far from the truth.

By the way, I could use some delicious

geological clam chowder right now, just like my mom

used to make, but with more nickel.

The lightest materials of all, including gases,

like hydrogen, helium, methane, water vapor, nitrogen, ammonia,

hydrogen sulfide, they bubbled to the surface,

and were kind of belched out of volcanoes to form

the early atmosphere of the earth-- the steam off the soup.

And then even more water vapor

was brought in my comets falling to earth.

Which we appreciate comets, but even though we do have

a water shortage, we don't need you to come back.

Much of the methane and hydrogen sulfide in the early atmosphere

was converted into carbon dioxide, which turned the sky

into like a terrifying red,

rather than our friendly blue of today.

So basically you've got an Earth with a red sky,

volcanoes that are thousands of feet high,

a black, barren, rocky surface, the foul smell

of sulfur everywhere, scalding hot steam,

constant collisions of fire and brimstone from above

occasionally splitting the crust open and creating

entire oceans of lava.

That's why we call this period in Earth's history

the Hadean Era, after Hades, the Greek god of the underworld.

But a couple nice things

about this crazy, terrifying, ball of fire.

One: we weren't there, so it's not bothering us.

Two: all of this intense heat and pressure allowed

mineral combinations to increase dramatically.

In fact, there were a whopping 1,500 different combinations,

and that would only increase as plate tectonics

and life got involved.

So during this terrible toddler phase for the Earth,

a Mars-sized object dubbed Thea collided

with the newly formed Earth in a vigorous kind of body check,

or I guess more of a planet check.

This knocked out a huge chunk of the Earth's materials,

and then over time, those materials accreted into,

you guessed it, the moon.

The moon of course is best known today for inspiring

the Moons Over My Hammy sandwich at Denny's,

but it also inspired the space race and millions of poems,

and paintings, and it also created tides.

But putting aside the tides, which are admittedly

a pretty big deal, without the moon what would

wolves howl at in all of those t-shirts?

All right, so as the Earth cooled,

the water vapor that had accumulated in the atmosphere

fell in torrential rains,

like downpours that lasted millions of years.

It was like Seattle, but instead of like coffee and grunge music

there was just ammonia.

These downpours created the first oceans.

Like as the Earth's surface

cooled below 100 degrees Celsius, water vapor was able

to stay in liquid form and somewhere between

3.8 and four billion years ago, we had oceans.

Let's talk about food again.

This time, though, instead of Earth chowder,

let's imagine the Earth as an egg.

The crust is as thin as the eggshell,

it's also brittle and fractured into segments called plates.

Essentially these plates float on top of squishy, goopy rocks

that are close to their melting point.

As a result, the surface of the Earth has a history of its own,

including the creation of mountains,

the explosion of volcanoes, the forging of

mighty super continents like Rodinia and Pangaea.

Plate tectonics affects everything from the movement

of continents to the distribution