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[Music]

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hello everybody my name is Justin Park I

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am a second year PhD student at

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Rensselaer Polytechnic Institute and one

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thing we're interested in doing in our

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Labs is reconstructing ancient

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atmospheres as they pertain to important

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evolutionary steps in our atmosphere's

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history

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so what I do is I look at ancient

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atmospheres trapped in halite fluid

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inclusions so halite as we've seen in

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previous talks is an evaporative mineral

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it forms in these really dry arid

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environments where evaporation is the

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dominating Force as it does so it can

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form these things called fluid

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inclusions as shown in the top right up

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here and they can encapture air or brine

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in the mineral Matrix now these can be

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primary or secondary meaning they form

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at the time the mineral precipitates or

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forming sometime later with some

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secondary fluid event and oftentimes

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they form an assemblages of hundreds or

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thousands of inclusions at once now what

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I'm interested in doing is looking at

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the gases that are trapped in these

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primary inclusions and saying something

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about the evolving composition of the

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atmosphere

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now we do have some evidence for what we

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think the atmosphere looked like and how

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it evolved here I have plotted one of

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the major models suggesting the change

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in partial pressure of nitrogen oxygen

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CO2 and methane as a function of time

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starting with the moon forming event 4.5

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billion years ago

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now if you'll notice here there is a lot

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of uncertainty in these measurements and

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this is due to them being made with

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indirect proxy measurements now also in

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the period between two and one billion

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years ago here

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we have this period known as the boring

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billion and it's aptly named for the

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apparent stagnancy of the atmospheric

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evolution

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now what we're interested in doing is

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providing ancient atmospheric

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constraints using fluid inclusions in

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the period between these two points

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using direct analysis from 1.4 billion

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year old fluid inclusions

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so we can do this by loading our samples

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into a special crushing device crushing

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them this ruptures our inclusions and we

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can pass the gas directly into a

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quadruple Mass spectrometer

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when we do so we see peaks in our signal

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that correspond to each Crush these

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Peaks can be integrated and Quantified

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by comparing to known calibration points

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thus we can get an idea of the

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composition and known amount of moles of

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nitrogen oxygen argon and CO2 present in

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these inclusions

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when we backtrack and calculate the

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ancient atmosphere composition we do

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have to be wary of any aqueous

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contributions as we know Henry's law

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tells us this atmosphere may also be

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dissolved in the brine phase and its

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equilibrium

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so when we did this we saw some

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variability in our results here I have

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plotted the mole fraction of nitrogen

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oxygen argon and CO2 as a function of

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the size of each sample one thing we can

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notice is that the primary and secondary

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inclusions do capture different

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atmospheres that are distinct from one

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of one another now we're very interested

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in the primary inclusions as that's the

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environment that the mineral formed in

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and we can compute a average partial

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pressure or density of each gas and

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compare it to the modern atmosphere

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when we do that we saw some very

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interesting things back 1.4 billion

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years ago we found atmospheric nitrogen

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was roughly the same partial pressure as

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it is today atmospheric oxygen was

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around a tenth as dense

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argon was about half as dense and carbon

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dioxide was actually eight times more

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dense now each of these gases has really

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important implications but due to time

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I'm only going to have time to talk

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about oxygen today

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so when we looked at our auction results

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there are measured partial pressure

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revealed some pretty interesting things

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here I have it compared to many of the

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predicted models that have been proposed

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what we saw is that we captured more

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oxygen than these models would have

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proposed this indicates that these

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direct measurements might be able to

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capture things that the proxies are

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unable to

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and this has some pretty important

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implications the oxygen that we measured

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is above theoretical lower limits

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necessary for the early evolution of

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life and it's also an agreement with

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some evidence suggesting there was a

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developed ozone layer at this time

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now on the right here I have plotted a

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phylogenetic tree showing the marked

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diversification of red algae in the

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mesopoterozoic Now red algae are very

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important as they're some of the first

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photosynthetic eukaryotes that gives

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them an evolutionary advantage to

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produce more oxygen than their

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predecessors

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it was really interesting when we

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compare this to our timing of the

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deposition of our samples we can see

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they're roughly contemporaneous and thus

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our elevated oxygen measurements are

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likely due to the presence of these red

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algae so I hope I've shown here today

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that the atmospheric oxygen here is

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pointing a more Dynamic picture of the

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boring billion and it might not have

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been so boring at all we have important

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implications of these ancient red algae

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evolving at this time period that led to

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this

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inclusions can capture and maintain

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direct evidence of ancient atmospheres

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for hundreds of millions of years if not

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billions

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with mass spectrometry we can probe the

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contents of the gas that are trapped

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within these and we can look into how

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the atmosphere has evolved we aimed to

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make compositional measurements of the

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atmosphere 1.4 billion years ago and we

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found something very different than our

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present atmosphere hopefully in the

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future we can make isotopic ratio

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measurements and see any further

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Evolution trends so with that thank you

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all for listening if you have any

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questions I'd be happy to talk to you

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about my poster number 14 after this

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[Applause]