Earth Formation How the Earth is a the byproduct of a local supernova
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- What I'm going to attempt to do in the next two videos is really just give an overview
- of everything that's happened to Earth since it came into existence.
- We're going start really at the formation of Earth or the formation of our Solar system or the formation of
- the Sun, and our best sense of what actually happened is that
- there was a supernova in our vicinity of the galaxy,
- and this right here is a picture of a supernova remnant,
- actually, the remnant for Kepler's supernova.
- The supernova in this picture actually happened four hundred years ago in 1604,
- so right at the center a star essentially exploded
- and for a few weeks was the brightest object in the night sky,
- and it was observed by Kepler and other people in 1604,
- and this is what it looks like now.
- What we see is kinda the shockwave that's been traveling
- out for the past 400 years, so now it must be many
- light years across. It wasn't, obviously, matter wasn't
- traveling at the speed of light, but it must've been traveling
- pretty, pretty fast, at least relativistic speeds, a reasonable
- fraction of the speed of light.
- This has traveled a good bit out now, but what you can
- imagine is when you have the shockwave traveling out from
- a supernova, let's say you had a cloud of molecules,
- a cloud of gas, that before the shockwave came by just
- wasn't dense enough for gravity to take over,
- and for it to accrete, essentially, into a solar system.
- When the shockwave passes by it compresses all of this gas
- and all of this material and all of these molecules, so
- it now does have that critical density to form, to accrete
- into a star and a solar system.
- We think that's what's happened, and the reason why we
- feel pretty strongly that it must've been caused by a supernova
- is that the only way that the really heavy elements can form,
- or the only way we know that they can form is in kind of
- the heat of a supernova, and our uranium, the uranium that seems
- to be in our solar system on Earth, seems to have formed
- roughly at the time of the formation of Earth, at about
- four and a half billion years ago, and we'll talk
- in a little bit more depth in future videos on exactly how
- people figure that out, but since the uranium seems about
- the same age as our solar system, it must've been formed
- at around the same time, and it must've been formed by a supernova,
- and it must be coming from a supernova, so a supernova
- shockwave must've passed through our part of the universe,
- and that's a good reason for gas to get compressed and begin to accrete.
- So you fast-forward a few million years.
- That gas would've accreted into something like this.
- It would've reached the critical temperature, critical density
- and pressure at the center for ignition to occur, for fusion
- to start to happen, for hydrogen to start fusing into helium,
- and this right here is our early sun.
- Around the sun you have all of the gases and particles
- and molecules that had enough angular velocity to not fall into the sun,
- to go into orbit around the sun.
- They were actually supported by a little bit of pressure, too,
- because you can kinda view this as kind of a big cloud of gas,
- so they're always bumping into each other, but for the most part
- it was their angular velocity, and over the next tens of millions of years
- they'll slowly bump into each other and clump into each other.
- Even small particles have gravity, and they're gonna slowly
- become rocks and asteroids and, eventually, what we would call
- "planetesimals," which are, kinda view them as seeds
- of planets or early planets, and then those would have a reasonable amount
- of gravity and other things would be attracted to them
- and slowly clump up to them.
- This wasn't like a simple process, you know, you could imagine
- you might have one planetesimal form, and then there's another
- planetesimal formed, and instead of having a nice, gentle
- those two guys accreting into each other, they might have
- huge relative velocities and ram into each other, and then just,
- you know, shatter, so this wasn't just a nice, gentle process of constant accretion.
- It would actually have been a very violent process,
- actually happened early in Earth's history, and we actually think
- this is why the Moon formed, so at some point
- you fast-forward a little bit from this, Earth would have formed,
- I should say, the mass that eventually becomes our modern Earth
- would have been forming. Let me draw it over here.
- So, let's say that that is our modern Earth, and what we think
- happened is that another proto-planet or another,
- it was actually a planet because it was roughly the size of Mars,
- ran into our, what it is eventually going to become our Earth.
- This is actually a picture of it.
- This is an artist's depiction of that collision, where this planet
- right here is the size of Mars, and it ran into what would eventually become Earth.
- This we call Theia. This is Theia,
- and what we believe happened, and if you look up,
- if you go onto the Internet, you'll see some simulations
- that talk about this, is that we think it was a glancing blow.
- It wasn't a direct hit that would've just kinda shattered
- each of them and turned into one big molten ball.
- We think it was a glancing blow, something like this.
- This was essentially Earth. Obviously, Earth got changed
- dramatically once Theia ran into it, but Theia is
- right over here, and we think it was a glancing blow.
- It came and it hit Earth at kind of an angle, and then it
- obviously the combined energies from that interaction
- would've made both of them molten, and frankly
- they probably already were molten because you had
- a bunch of smaller collisions and accretion events and
- little things hitting the surface, so probably both of them
- during this entire period, but this would've had a
- glancing blow on Earth and essentially splashed a bunch
- of molten material out into orbit.
- It would've just come in, had a glancing blow on Earth,
- and then splashed a bunch of molten material,
- some of it would've been captured by Earth, so this is
- the before and the after, you can imagine, Earth is
- kind of this molten, super hot ball, and some of it
- just gets splashed into orbit from the collision.
- Let me just see if I can draw Theia here, so
- Theia has collided, and it is also molten now because
- huge energies, and it splashes some of it into orbit.
- If we fast-forward a little bit, this stuff that got splashed
- into orbit, it's going in that direction, that becomes
- our Moon, and then the rest of this material eventually
- kind of condenses back into a spherical shape and is what
- we now call our Earth.
- So that's how we actually think right now that the Moon
- actually formed.
- Even after this happened, the Earth still had a lot more,
- I guess, violence to experience.
- Just to get a sense of where we are in the history of Earth,
- we're going to refer to this time clock a lot over the next few videos,
- this time clock starts right here at the formation of our solar system,
- 4.6 billion years ago, probably coinciding with
- some type of supernova,
- and as we go clockwise on this diagram,
- we're moving forward in time, and we're gonna go
- all the way forward to the present period,
- and just so you understand some of the terminology,
- "Ga" means "billions of years ago"
- 'G' for "Giga-"
- "Ma" means "millions of years ago"
- 'M' for "Mega-"
- So where we are right now, the Moon has formed,
- and we're in what we call the Hadean period
- or actually I shouldn't say "period."
- It's the Hadean eon of Earth.
- "Period" is actually another time period,
- so let me make this very clear. It's the Hadean,
- we are in the Hadean eon, and an eon is kind of
- the largest period of time that we talk about, especially
- relative to Earth, and it's roughly 500 million to a billion years
- is an eon, and what makes the Hadean eon distinctive,
- well, from a geological point of view what makes it
- distinctive is really we don't have any rocks from the
- Hadean period. We don't have any kind of macroscopic-scale
- rocks from the Hadean period, and that's because
- at that time, we believe, the Earth was just this molten
- ball of kind of magma and lava, and it was molten
- because it was a product of all of these accretion events
- and all of these collisions and all this kinetic energy turning into heat.
- If you were to look at the surface of the Earth,
- if you were to be on the surface of the Earth during
- the Hadean eon, which you probably wouldn't want to be
- because you might get hit by a falling meteorite
- or probably burned by some magma, whatever,
- it would look like this, and you wouldn't be able to breathe anyway;
- this is what the surface of the Earth would look like.
- It would look like a big magma pool, and that's why we
- don't have any rocks from there because the rocks were
- just constantly being recycled, being dissolved and churned
- inside of this giant molten ball, and frankly
- the Earth still is a giant molten ball, it's just
- we live on the super-thin, cooled crust of that molten ball.
- If you go right below that crust, and we'll talk a little bit more
- about that in future videos,
- you will get magma, and if you go dig deeper,
- you'll have liquid iron.
- I mean, it still is a molten ball.
- And this whole period is just a violent,
- not only was Earth itself a volcanic, molten ball,
- it began to harden as you get into the late Hadean eon,
- but we also had stuff falling from the sky and constantly
- colliding with Earth, and really just continuing to add
- to the heat of this molten ball.
- Anyway, I'll leave you there,
- and, as you can imagine,
- at this point there was no, as far as we can tell,
- there was no life on Earth.
- Some people believe that maybe some life could've formed
- in the late Hadean eon, but for the most part
- this was just completely inhospitable for any life forming.
- I'll leave you there, and where we take up the next video,
- we'll talk a little bit about the Archean eon.
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At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
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