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okay so thanks everybody who's here for

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this afternoon talk I know lunch was

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delicious and you're all probably

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looking forward to a nap at some point I

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want to point out that most of the heavy

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lifting for this project has been done

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by an undergrad in our lab James

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seancody he does fantastic work and a

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lot of this is thanks to him so on the

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present earth we have about twenty one

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percent oxygen and about one part per

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million methane and this is a direct

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result of life on Earth oxygen as a bio

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signature then is this grand idea that

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the microbial community can dramatically

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alter the atmosphere of a planet just

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over fairly short time scales in Earth's

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history and this idea traces back to

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love lock in the 60s as eugenio

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mentioned where he first posited that we

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could look for oxygen in combination

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with hydrocarbons so for example in the

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modern atmosphere we have oxygen and

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methane as a bio signature for life on

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another planet and not to poke fun at

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Daniel but the habitable zone is a

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really great place to look for life

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because it's on the surface and it's

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modifying the atmosphere if and in

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conjunction with that it's also much

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easier to get photons from habitable

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zone planet than it is from a moon

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around a Jupiter so terrestrial planets

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in the habitable zone are great place to

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look for life as I said Lovelock

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pioneered this in the 60s and it's been

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modified and updated throughout time we

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figured out that while oxygen is a great

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tracer for life ozone is a tracer for

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oxygen and we can use that in place of

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that there's a much larger spectral

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fingerprint for ozone and so it's

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evolved from oxygen the ozone and the

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ozone and combination with those

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reducing compounds that we talked about

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before now another reason why we're

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looking for bio signatures

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terrestrial planets in the habitable

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zone is because of our neighbors so

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early in the solar system history when

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Venus was getting pummeled by radiation

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from the Sun it underwent a runaway

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greenhouse and most of its water vapor

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got into the upper atmosphere was

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dissociated and the hydrogen

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subsequently lost to space that hydrogen

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loss is Daniel mentioned can trigger the

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build-up of oxygen in an atmosphere

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that's not related to life if you lose

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an ocean of water from Venus you can get

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up to 240 bars of molecular oxygen just

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from that ocean by losing all the

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hydrogen so on the interior of the

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habitable zone towards a sun-like star

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you could destroy a planet but still get

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a transient oxygen signal on the

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exterior of the habitable zone our

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smaller cousin Mars currently has two

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tenths of a percent of molecular oxygen

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in its atmosphere this is a big deal

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this is if Mars was slightly larger it

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would have held on to more of its oxygen

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and subsequently Mars would look like a

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biological planet in terms of oxygen so

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that we would have to look for these

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secondary signposts these reducing

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compounds in conjunction with these

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oxidizing compounds to disentangle what

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processes are happening in that

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atmosphere and so the habitable zone for

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terrestrial mass planets is the place to

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look for bio signatures and that's why

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using oxygen as a bio signature for

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terrestrial mass planets is such a big

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deal it's it's here where we find that

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life is the cause of oxygen build up in

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the atmosphere not anything else or

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that's what we hope anyway in this study

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we're employing a one-dimensional

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horizontally averaged photochemical

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model like Eugenio mentioned the casting

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group has had numerous versions of this

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code but it essentially boils down to

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tens of kilometers tall test tube where

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photons come in the top and we have

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and gases and ran out moving chemicals

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at the bottom of the atmosphere and in

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the middle we have a steady-state

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chemical disequilibrium that's caused by

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the fluxes in an amount in and out of

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our atmosphere and so for the runs I'm

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going to talk about today we're in a

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ninety percent co2 atmosphere so it's

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going to be moved towards the outer edge

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of the habitable zone otherwise it's

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going to be a little too warm and go

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into a runaway you know one bar

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atmosphere and our base-case volcanism

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we're putting out sort of the upper end

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of what we think of a terrestrial mass

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planets volcanism so we're putting out

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hydrogen and methane and hydrogen

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sulfide and then when we reduce volcanic

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outgassing we're just leaving in h2 us

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which is commensurate with what some of

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the more recent results for oxygen false

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positives have pointed out as being an

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initiator for their runaway oxygenation

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so just to give you guys a little

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background I'm going to talk about redox

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because that's what I do so we define a

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system of redox with these neutral

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species that things are moving towards

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the chemical other chemical species are

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being pushed towards the redox neutral

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species so in our case we define neutral

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as water co2 and so2 and so for example

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a reduced chemical species like methane

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when combined with water vapor gets you

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back to co2 which is one of our other

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neutral species but gets you an excess

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of hydrogen and so the reducing species

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give you hydrogen in the redox budget on

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the other end of things the oxidized

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species like hydrogen peroxide you have

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to add hydrogen to get them back to that

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base redox neutral species and so in

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this case hydrogen peroxide has a net

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minus 1 h2 molecule so just for some

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audience participation who knows what

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the redox number for h2so4 is can you do

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the math in your head anybody was that

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h2so4

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well you say you're I guess I should

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explain this a little better so you're

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going to take h2so4 and you're going to

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add either hydrogen or one of the redox

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neutral species and either you're going

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to evolve hydrogen or give back to the

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neutral species so just to skip to the

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punchline h2so4 is a net minus one

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hydrogen and then CEO is a net plus a

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half hydrogen or plus 100 n see even I

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can't keep it straight so this is our

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model like I said we have a big test

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tube where we're putting volcanic gases

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into the bottom of the model and we

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assume that there's an ocean covering

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this planet that's only really in one

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dimension we're working on that so you

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have volcanic gases that are being

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evolved out of the subsurface

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essentially through the ocean layer and

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into the atmosphere you have rain out of

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reducing species and oxidizing species

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that accounts for redox at the ocean

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atmosphere boundary and then you have

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the escape of reducing species at the

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top of the atmosphere now on long time

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scales the influx of volcanic gases

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which are consistently reducing so we

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have methane and hydrogen sulfide and h2

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that are being evolved into the

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atmosphere on long time scales the

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volcanic gases are balanced by hydrogen

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escape and so what's happening in the

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atmosphere ocean boundary is important

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but it's not the principal control on

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atmospheric redox on long time scales

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and so what I'm going to do now is I'm

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going to show you a really scary table

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and I'm going to point out that here

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where who would all have no hydrogen

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emission where they have a prodigious

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amount of oxygen it's about a tenth of a

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percent of the lower boundary they have

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an imbalance in the fluxes of reducing

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components and oxidizing components at

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the atmosphere ocean boundary but if you

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were to look at the fluxes of hydrogen

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here hydrogen h2 + H to the fluxes of

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h2s what

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is there volcanic constituent the

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volcanic component is much larger than

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the escape of hydrogen to space so they

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should be gaining hydrogen in their

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atmosphere the atmosphere should be

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coming beep excuse me should be becoming

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more reducing with time not more

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oxidizing and so the fact that this

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lower boundary is not balanced is a

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problem and a problem that we can fix by

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returning that hydrogen returning that

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imbalance to the atmosphere and so

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balancing the atmosphere ocean redox

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budget is a key component of

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understanding the integrated redox state

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of these atmospheres so I mentioned

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solar-type stars and how we have false

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positives around the habitable zone but

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not in it we haven't seen a conclusive

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case of a total atmosphere ocean redox

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system that's been balanced that

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generates an oxygen false positive the

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2012 results from Rena hue and all are

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indicative of an imbalance at the ocean

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atmosphere boundary but not indicative

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of a false positive in the context of an

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atmosphere ocean system that's totally

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balanced but we have to look at other

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stars as well we're not going to fund

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we're not just going to look at

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terrestrial mass planets and have little

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zone of solar type starts we're going to

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look around M stars and K stars because

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they're just easier to observe habitable

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zone planets around and so here for my

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model results I have the Sun and green I

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apologize for those of you who are

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red-green colorblind I did try to make

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this as friendly as possible but the Sun

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is in green we have HD 2204 9 which is

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AK 2 star so that's slightly less

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massive than the Sun and then we have

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two M Dwarfs we have a dealio which is a

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classic very active M star that flares

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occasionally it's a pretty exciting for

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any planets that might be around it and

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then we have g GJ 876 which is a

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slightly less massive slightly cooler m

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star

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in red here and so if we were to take

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these stars with the same atmospheric

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parameters the same fluxes of gases the

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same parameterization of rain out and do

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model runs I'm going to show you a

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really scary figure with lots of lines

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would just stick with me so we see that

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four major constituents like water vapor

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and co in the base case which is the

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left-hand side so remember we're getting

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more volcanic outgassing in the

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left-hand cases your left on line you

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get pretty consistent atmospheric

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profiles across different stellar types

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but it's really when you get down here

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to where we're looking at the oxygen

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bearing species that something stands

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out and so here around GJ 876 we get

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about 10 to the minus 7 oxygen at the

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lower boundary which is somewhere

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between 6 and 10 x 10 orders of

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magnitude more oxygen than every other

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star in our model excuse me so this is

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just the base case where we have lots of

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volcanic out casting lots of reducing

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power going into the atmosphere if we

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turn down the volcanism not turn it all

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the way off just turn it down to a

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minimal level we're still putting

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reducing compounds into the atmosphere

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you get something like we see on Mars

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where we're nearly at a tenth of a

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percent oxygen at the lower boundary and

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this is a big deal if you were to

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continue to turn down volcanism on a

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terrestrial mass planet in the habitable

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zone you would get a runaway oxygenation

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you would get this false positive around

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an m-dwarf which is probably where we

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are going to find our first to rest room

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last planet where we're going to do our

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first spectroscopy where we're going to

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find this signpost that we think is

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infallible and so this result here is

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preliminary I won't say it's conclusive

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but it is indicative that there's a lot

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of work to be done on understanding how

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M Dwarfs how the spectral

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fluxes effect atmospheres especially in

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the context of bio signatures so we find

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this false positive lurking for high CO

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2 atmospheres future work we're going to

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look into actually keeping track of

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aqueous chemistry currently we're just

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returning reducing power to the

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atmospheres hydrogen it's not the best

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but we don't have a firm grasp on what

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aqueous chemistry is going to look like

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on an alien world so future work also

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will include exploring what parts of the

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stellar radiation are influencing this

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oxygen false positive so if we turn down

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for example the far UV radiation or the

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near UV radiation what's going to cause

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us to build up oxygen because every star

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is not alike and so we need to

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understand where in the stellar

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parameter space we're going to find

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these planets that look like they have

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life but probably don't and so with that

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yeah Thank Chester so no one cares about

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you Eric thanks honey yeah if you go

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back to your figures your four figures

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slide what's the main constituent of

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your atmosphere is it n to know these

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are ninety percent co2 atmosphere so n 2

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is a very minor component of these ok I

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see any don't blood co2 here ok well I

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mean so we set co2 is a fixed mixing

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ratio and I mean there have been studies

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that have used it as a as an actual

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variable chemical constituent but

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there's not really much of a difference

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between at these levels whether it's a

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fixed mixing ratio or variable chemical

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constituent thanks I do have a quick

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question so from from the observation

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decide what kind of telescopes do we

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need to observe stuff like that is that

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possible with James Webb or more with

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like next-generation telescopes that's

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actually a really good question for

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Natasha I think that the standard

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understanding is that a tenth of a

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percent oxygen is detectable with the

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next generation of telescopes so the

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oxygen false positives we see for

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reduced volcanic outgassing could be a