The Sun & The Earth: Crash Course Big History #3


Hi, I’m John Green, this is Crash Course Big
History. Today we’re gonna 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 linchpin 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 unlikable. But regardless, the word “planet” is a man-made
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!? [Theme Music] 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 of the matter of 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- 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 of 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 gasses 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 10 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 10 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 teaming 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 7 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 kinda 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
by 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 the 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, scolding 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 of 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-size object dubbed Theia 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 4 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 and evolution of species, and is one of the
most vital principles of modern geology. It’s also responsible for less fun things, like
massive earthquakes and super volcanic eruptions that have caused the deaths and even total
extinction of millions of species. Finally, the point should be raised that of
all the possible scenarios that might kill off the human race — provided we don’t kill
off ourselves — a super volcanic eruption is among the foremost of them. In fact, on
the scale of millions of years, a devastating eruption is almost guaranteed to happen. And
unlike an asteroid, one can’t go all Bruce Willis and blow up a super eruption with a nuke. If we’re
still around, it’ll be interesting to see how we cope. Throughout the birth of the Sun and the origins
of the Earth, there was the chance formation of Goldilocks conditions for life. Like with the porridge and beds that a fairy-tale
sociopathic blonde pilfered from a baby bear in a break-and-enter job, the conditions for
life on Earth were just right. This includes the placement of the planet relative to the
Sun. The right chemicals were present on Earth to produce the first building blocks for life
— more on that next time. Even plate tectonics were hugely important.
First, they suck biotic waste — dead things, excrement — underground instead of remaining
on the surface. If not for plate tectonics, we’d be more more-or-less swimming in our
own you-know-what. Over millions of years, this biotic waste could be transformed into
coal, or even diamonds. Plate tectonics – we turn your poo into diamonds. And if it wasn’t for oceans and plate tectonics,
there’s a good chance that we’d have the same runaway greenhouse effect that Venus has – where
the surface is hot enough to melt lead. Plate tectonics were also crucial to human
history. The gigantic land-mass of Afro-Eurasia made trade networks possible, which facilitated
the exchange of knowledge and technologies, along with sharing diseases to gradually build
immunities — something that would be grave news for the isolated inhabitants of North
and South America. The distribution of copper, iron, silver and
gold influenced the growth and prosperity of countless societies, even the distribution
of coal-beds in Wales was a major ingredient for the industrial revolution kicking off
in Great Britain. All these things, formed within the slimmest
of margins of probability, were Goldilocks conditions for the rise of complexity in the
later story — the sustenance of life, the distribution of resources, and even the coal
needed for the industrial revolution, which exploded into the tremendous rise of
complexity in modern times. It’s a transformation that continues to this very day. So speaking of Goldilocks conditions, knowing
about the formation of our solar system, and the conditions on Earth that were necessary
for life, is crucial to thinking about the possibility of life elsewhere. The first so-called
exoplanet was discovered by Swiss astronomers in 1995, and in 2002 alone, 31 new exoplanets
were discovered by independent astronomers. NASA has taken this several steps further.
In 2009 they launched the Kepler probe to look at about 150,000 solar systems in
the nearby galaxy. As of now, they’ve found hundreds and hundreds
of confirmed planets with thousands more potential candidates. And estimates are that in the
entire Milky Way galaxy, there could be as many as 40 billion Earth-sized planets orbiting
their stars in the Goldilocks zones for life, and that’s just in our galaxy! There are hundreds
of billions of galaxies in the universe. Now I’m not gonna tell you that creating life
is as easy as shooting fish in a barrel, but if you put a hundred trillion bullets in that
barrel, you are bound to hit a fish. But given the vast amount of space between solar systems
and the fraction of time in which life — to speak nothing of the sliver of time so-called
“intelligent life” — has existed on our planet, we may never encounter other life forms. But I find it tremendously exciting, as well
as kind of comforting, knowing that there may well be other forms of life out there,
even if we never run into them, from microbes to multi-celled organisms, like, you know…us!
Maybe they’re as astonished by their existence as we are by ours, and thinking about that,
one begins to feel a little bit better about our tiny role in the cosmic play. We may never
meet, but we’re comrades in the strange phenomenon of rising complexity in the universe. More
on that next time. I’ll see you then.

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