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  • 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!?

  • 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.