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Current time:0:00Total duration:10:08

Video transcript

what I'm going to attempt to do in the next few videos is really just given overview of everything that's happened to earth since it came in to existence and we're going to 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 400 years ago in 1604 so right at the center a very 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 so this is what we see is kind of the shockwave that's been traveling out for the past 400 years and 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 be true it must have been traveling pretty pretty fast at least relativistic speeds we're a reasonable fraction of the speed of light so this has traveled a good bit out now but what you could imagine is is when you have the shockwave traveling out from a supernova let's say you had a let's say you had a cloud of molecules a cloud of gas that before the shockwave came by it just wasn't dense enough it wasn't dense enough for gravity take over and for it to accrete essentially into a solar system but when the shock wave passes by it compresses 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 so we think that's what's happened the reason why we we feel pretty strong it's pretty strongly that it must have been caused by a supernova is that the only way that the really heavy elements can form or the only way that 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 4 and 1/2 billion years ago and we'll talk 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 have been formed at around the same time and it must have been formed by a supernova and it must be coming from a supernova so a supernova shockwave must have 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 ago that gas would have created into something like this it would have 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 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 kind of 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 going to slowly get become rocks and asteroids and eventually what we'd call planetesimals which are really kind of view them as as seeds of planets or early planets and then those those would have a reasonable amount of gravity and and other things would be attracted to them and slowly clump up to them but this wasn't like a simple process you know you could imagine you might have one planetesimal form and maybe there's another planetesimal form and instead of having a nice gentle those two guys are creating 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 actually 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 from this earth would have formed I should say the the 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 what is eventually going to become our earth and this is actually a picture of it this is an artist's depiction of that collision where this this planet right here is the size of Mars and it ran into what eventually would become earth and this we call Thea this is Thea 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 that it wasn't a direct hit that would have just kind of shattered each of them and turn them to one big molten ball we think it was a glancing blow something like this so if this was this was essentially earth obviously earth got changed dramatically once the ran into it but Thea is right over here and we think it was a glancing blow where it came and it hit earth it hit her at kind of an angle and then it obviously the combined the energies from that interaction would have 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 of probably both of them during this entire period but the the this would have had a glancing blow on earth and essentially splashed a bunch of molten material out into orbit so it would have just come in had a glancing blow on earth and then splashed a bunch of molten material some of it would have been captured by earth so this is the before and then the after the after you could imagine earth is kind of this molten super hot ball super hot ball and some of it just gets splashed into orbit splashed into orbit from the collision and let me see if I can draw Thea here so Thea is Thea has collided and it is you know and it's it's also molten out because huge energies and it splashes some of it into orbit and if we fast forward a little bit this stuff that got splashed into orbit the stuff that got splashed into orbit it's going in that direction that becomes our moon and then the rest of this we'll eventually kind of condenses back into a spherical shape and is what is we now what we now call our earth so that's how we actually think right now that the moon actually formed and even after this happened the earth still had a lot more I guess violence to experience so just to 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 going to 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 with the moon has formed we're in what we call the Hadean period or actually I shouldn't say period it's the Hadean Eon of Earth the period is actually another time period so let me let me make this very clear it's the Hadean we are in the DN a-- DN 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 from a geological point of view of what makes it distinctive is it's 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 believed the earth was just this molten ball of kind of magma and lava and it had and it was molten because it was the product of all of these accretion events and all of this all of these collisions and all of this kinetic energy turning into heat so 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 no pool and that's why we don't have any rocks from there because the rocks were just constantly being constantly being recycled being dissolved and and and and churned it inside of this this giant molten ball and frankly the earth still is a giant molten ball it's just we live on the 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 irons I mean it still is a molten ball and this whole period is just a violet not only was earth itself volcanic molten ball it began to harden as you get to the late Hadean Eon but we also had stuff falling from the sky and constantly 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 this point there was no as far as we can tell there's no life on earth some people believe that maybe some life could have formed in the late Hoddy an eon but for the most part this is completely inhospitable for any life forming so I'll leave you there and we're going to where we take up the next video we'll talk a little bit about the Archaean Eon