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better yeah okay so this is sort of the

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canonical model of mass and radius and

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in this paper she wrote drew this blue

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line and said that is sort of the earth

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like line and a lot of these planets

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including earth and venus went through

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this line and then they sort of came up

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with his tautological saying that says

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planets inferred to be earth-like are

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indeed earth-like and that has a lot of

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implications so the question then we ask

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is well what does it really mean to be

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earth-like and then you can ask this

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even more existential question of is the

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earth even special if we can just fit

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all of these planets with this curve so

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I want to take a step back and actually

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look at the data we take for exoplanets

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so here is a different way to plot a

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mass radius model so this is data not a

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model this is radius on the x-axis and

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density and I've color coded the mass

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and you can see we've got some variation

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we've got some low density high radius

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and high density low radius and that may

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tell us something about the fraction of

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rock to core maybe something about gas

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envelopes it's very coarse in this model

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terrestrial planets are right here earth

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Venus mercury and Mars we also have

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another data set that is sometimes

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overlooked which is the actual

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composition of the host stars so here is

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a about a thousand stars from a sample

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of F G and K stars my flooded magnesium

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silicon versus iron silicon these are

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sort of terrestrial planet ratios the

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Sun is in blue red have observed planets

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we can see some spread and magnesium to

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silicon and some spread an iron to

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silicon and maybe this tells us

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something about the core size if you

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have a bigger core you should have more

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iron relatives of silicon and magnesium

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silicon is really the measure of what a

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planetary mantle should be made of

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particularly at mineralogy so really the

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focus of my PhD which I just wrapped up

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earlier this year was trying to connect

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these two datasets can we talk about how

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connecting the stellar data with the

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planetary mass radius data so to do that

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I want to then think about earth-like

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planets and i want to say okay well

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we have this earth like model can we

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even fit the earth to an earthlike model

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so if we're going to be extrapolating up

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to 5 earth masses let's make sure we get

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the earth rate so I I'm going to put

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this in mass and Composition space

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because connecting stars and planets and

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here's the earth I was silicon to iron

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ratio of 1 and 1 earth-mass ignore that

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blue line for now but if we were to see

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the earth what we would observe the

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earth we wouldn't be able to take it

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spectra we would have to take the sun's

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so the Sun has a slightly higher silicon

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iron ratio so we're just going to look

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at the Sun for now and this is the

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planet we're going to model we're going

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to model a one earth radius planet and

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so this is where you should pay

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attention in the blue one if you

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actually modeled a one earth radius

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planet using what we know about the

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earth as earth scientist you

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overestimate the mass of the Earth by

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about thirteen percent so that Earth

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model that canonical earth model is

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wrong and I can tell you some reasons

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why so one thing is they don't have an

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upper mantle in their model that seems

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obvious they just basically extrapolate

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bridgeman aight all the way up to the

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surface and they use a solid iron core

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whereas we know for the most part the

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core is liquid and we should expect

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liquid iron cores on most terrestrial

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planets just if you look at the phase

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diagram of iron terrestrial earth-sized

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planets and up and will keep the

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magnesium silicon ratio of the mantle at

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one that just makes easy so if you run

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this model my model you actually still

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overestimate the mass of the Earth by

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about five percent but that's good

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because we also were adding details to

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the spherical cow model I'll skip that

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so one thing that makes a difference in

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the Earth's mass is that the core is not

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pure iron it has some amount of light

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elements in it and you can choose your

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favorite light element so carbon and

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oxygen will definitely change the mass

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of the core but it does not change the

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silicon to iron ratio that much sulfur

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has a bigger effect silicon has a very

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large effect because it's in the

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numerator and somewhat in the

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denominator but you can see that we can

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change the mass the planet as well as

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it's silicon iron ore are inferred

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silicon to iron ratio and the other

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thing we can also you can choose sort of

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an optimum from mineral physics of what

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we think the Earth's core is like so

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let's benchmark to the earth and sort of

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compare across so this is some amount of

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silicon and oxygen we can also change

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the magnesium to silicon

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issue of the mantle and see how that

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changes our silicon to iron ratio and

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the mass and really from this you can

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see core density changes has a large

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effect on silicon to iron ore and mass

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whereas changing our the magnesium

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silicon ratio of the mantle has a small

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effect on mass but a large effect or a

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somewhat effect on silicon and iron and

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there's the Sun which falls nicely in my

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model and if you take an earth model

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which is sort of by this green box some

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core density between about five and ten

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percent less than iron and a magnesium

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silicon ratio of the mantle which you

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can look at the mantle xenoliths and

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maybe get an idea of the mantles

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magnesium silicon ratio falls in that

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green box so in this plot I've reverse

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engineered the earth using the Sun

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that's pretty cool so in this sense for

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my barely course order of magnitude

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model I've the Sun is a good proxy for

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the earth so if you're going to tweet

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that's we should so if you can expand

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that we earth is great but let's talk

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about earth-like planets across the mass

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radius spectrum so here is radius versus

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silicon to iron in astronomy units and

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I'll tell you why it's an astronomer

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unit in just a second and what this says

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is if you have radio or if you have

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planetary radius which is what you would

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get from a transit method you have to

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actually follow up to get a mass

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measurement while you're there you might

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as well measure the stellar composition

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and get a silicon to iron ratio and from

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that you can actually oh these contours

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are contours of constant mass so you can

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run across say oh well there's my planet

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and then this earth like range is just

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the core size that is bound by the Sun

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and the earth true silicon iron ratio so

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next up is well is that a true

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assumption is the sun's composition a

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good proxy for the earth from a chemical

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perspective or from a Cosmo chemist

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perspective so this is how I defend that

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so this is the photospheric abundance

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versus the c1 chondrites which is one

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earth model for what the earth might be

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made of so iron and silicon magnesium

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are all elements that are refractory and

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what that means is if you're if you have

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a gas these will condense first at very

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high temperatures so in this one to one

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line which is in green you can see those

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three elements following falling nicely

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on it oxygen is a little bit above and

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I'll talk about that

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second so you can then make the next

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step and look at the actual earth

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abundance for some earth compositional

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model versus photosphere and again those

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are pretty close to that one to one line

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but oxygen is not and that's important

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because the earth is not made of just

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refractory metals they are oxidized

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species so if you were to use the sun's

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oxygen abundance you would actually over

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predict the total oxygen budget of the

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planet by a factor of eight or so which

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means you would oxidize everything there

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would be no core and that's not the

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planet we live on and that kind of makes

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sense oxygen is a volatile element you

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would think of so we need to make some

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correction for on the oxygen its to

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basically turn it into what I call

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refractory oxygen to say this is the

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oxygen abundance that or some

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approximation of the oxygen abundance of

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a planet and I'm always sticking with

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the earth because I want to benchmark to

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the earth and then expand that model

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outwards just to make actual comparisons

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across the exoplanet data set so to do

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that you need to create the phase

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diagram for a solar gas and this is a

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you may have heard of it also called

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condensation sequences so you would take

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a very hot gas and let it cool down and

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see which solids form first so I show

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aluminum even though aluminum is a dinky

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element with regards to planets it's the

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it's the coolest phase diagram because

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you can see everything that goes on so

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you start up really high we have mono

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atomic gases then you start forming more

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complex things like aluminum gas and a

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LOH and then the solid start forming you

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get things like corundum a really

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refractory mineral but eventually it all

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settles down to things like an earth

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aight and but this inner thigh here says

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that for every aluminum atom i may form

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a planet with i carry eight moles of

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oxygen so then you can start playing

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stoichiometry games so here is probably

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which was surprising to me is not often

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thought of the oxygen phase diagram so

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here you start high and you get some

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these cais which are these dashed lines

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but then really things we think about

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form terrestrial planets forced to write

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enstatite are the main host of oxygen

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and total about 23% for this solar model

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fall into oxygen is refractory so that

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would be your sort of

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estimate of your oxygen budget with

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which to build planet which is my very

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simple super duper planet if you have

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those four elements and later two more

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but for the most part you can describe

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the earth really well in its structure

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in its mineralogy with those four

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elements for the bulk of the mantle and

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00:09:17,590 --> 00:09:15,800
the upper mantle so let's look at it in

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a different way so this is the same

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thousand stars i showed earlier just on

253
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a ternary so here's iron magnesium and

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silicon the red are that is the same

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data set i showed earlier the black are

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the kepler stars and there's the Sun

257
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sort of right smack in the middle now so

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you can run you've now you've got iron

259
00:09:38,830 --> 00:09:37,010
magnesium silicon and oxygen you can

260
00:09:40,480 --> 00:09:38,840
calculate the weight percent of the core

261
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or the core mass percent which are these

262
00:09:45,250 --> 00:09:43,790
contours here so the Sun great falls

263
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exactly kind of where we expected

264
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between 30 and 35 mass percent of a core

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the real answer is about 33 32 so good

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we've now shown or I we had to their

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stellar diversity and planet diversity

268
00:10:02,380 --> 00:10:00,980
are linked so why would I would predict

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00:10:04,720 --> 00:10:02,390
that little black spot if it had a

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00:10:07,720 --> 00:10:04,730
planet this probably has a very high

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core fraction as well mass fraction and

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there may be populations it's a little

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hard to see here but there's a bit of a

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lobe and then you've got sort of this

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spread what do those planets look like

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what's the true diversity so this is

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something where I am giving a talk at an

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astrobiology conference but I think of

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things in planetary diversity not

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planetary habitability I want to

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understand how likely are Earth's so

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that's because now I'm of course

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completely talk myself into a corner

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because I want to talk about

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habitability now so this is a really

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crummy picture of tectonics so if you

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shut off tectonics of course you it does

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a great job of regulating the atmosphere

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so you're pumping carbon in and this has

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of course heat problems for how your

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core crystallizes so one thing I'll talk

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about really quickly is one thing that

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controls tectonics which may control

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habitability is buoyancy of the plates

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so as a plate goes down it undergoes a

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phase transition it becomes a really

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terrible term negatively buoyant and

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keep sinking and it's one of the things

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that helps power plate tectonics

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it's also a purely chemical process well

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chemical and mineral physical property

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so i want to know within this sample

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which one of these which of these

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compositions are likely to produce

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planets that can undergo that phase

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transition and become successfully

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negatively buoyant and keep sinking so

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this is sort of big data planetary

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science and just asking the question how

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common is our negatively buoyant plates

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I'm not saying whether plate tectonics

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is occurring I'm just saying if it did

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what what is the likelihood so we need

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to melt everything and basically get an

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idea of what the basaltic crust is and

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then make the phase diagrams so here is

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your basalt phase diagram this is for

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our earth model again benchmarking to

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the earth and here's your basalt you

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integrate the differences in density

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down at whatever depth you want and you

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can calculate a buoyancy force so here

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is and these are preliminary results

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they're almost done the papers written

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we just need to finagle so this is

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magnesium silicon vs. net buoyancy force

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running through a lot of chemistry that

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if you're interested I can talk about

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and I've made a line for the model earth

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and only about 5% of that total thousand

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star sample actually works to create

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negatively buoyant plates so I'll leave

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it here my real point which I've

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underlined here is that earth-like does

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not mean compositionally similar it may

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not even mean the atmosphere is the same

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it behaves like the earth because

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tectonics dynamics are really what's

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powering all of us and we all need to

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work together to solve the problem so

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alright question already thank you

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regarding up plate tectonics and also a

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buoyancy of mental material how do you

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rectify similar chemical composition

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between Earth and Venus and and

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excellent question so this I I Venus is

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always gonna dog this question if the

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sun's composition is similar then Venus

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and Earth should be exactly the same so

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right now we're working on getting

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mixing to understand maybe something

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Venus or earth form slightly differently

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or that we're not taking into account

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actual discs mixings or something like

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that and then if we see that that

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doesn't work we're going to will add

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extra details of history you know what

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happened to make and sort of it's sort

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of its constraining Earth and Venus from

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the outside like what doesn't work

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versus what did work and we'll add

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details as we go but I am really

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interested in Venus and I think thinking

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of Earth and Venus as sort of the ideal

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and not ideal exoplanet and

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understanding the differences is a

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really profound way of understanding all

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of X of planetary science Thank You

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yeah so is there any worried that the

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dynamics like how you form these planets

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sort of obscures the link between

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Stemler composition and planetary

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encompasses yeah so right now I'm

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working I just started my postdoc

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working on integrating so the the

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condensation sequence code I've written

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with mixing models to sort of get an

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idea of feeding zones so one of the

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things in this this plot here is I show

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I bound by the earth and the Sun but

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Venus doesn't actually work unless you

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use a slightly higher magnesium to

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Silicon number for the for the mantle

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and that's interesting because in the

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oxygen phase diagram you get something

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00:15:01,070 --> 00:14:58,320
of mg mg / SI of two condensing before

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00:15:03,200 --> 00:15:01,080
mgs I of one so if you preferentially

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00:15:05,930 --> 00:15:03,210
mix from higher temperature closer to

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00:15:08,450 --> 00:15:05,940
your star stuff you might expect high

390
00:15:10,910 --> 00:15:08,460
mgs I so that's worth figuring out what

391
00:15:13,010 --> 00:15:10,920
up adding a dynamical component saying

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00:15:14,990 --> 00:15:13,020
this is where it fed from here's what

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00:15:16,490 --> 00:15:15,000
the stuff the chemistry of the stuff

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that formed from now run the

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00:15:21,440 --> 00:15:18,390
stoichiometry and figure things out so