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[Music]

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[Applause]

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so I'm gonna talk a bit about how we try

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to apply understanding energetics and

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biological systems on earth to these

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questions that we've been hearing about

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all week and in the plenary this morning

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about how could we tell if there might

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be life on ocean worlds and so it's

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really difficult because we don't often

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know a lot about the specific oxidants

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or reductants or gradients in these

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ocean worlds and even on earth it's

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really hard to predict what kinds of

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redox reactions even abiotic ones you

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might find in any particular environment

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so we've been working a lot with the JPL

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electric chemical technologies group who

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is a big leader in building batteries

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and fuel cells and interesting

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conditions for spaceflight and so we've

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been trying to apply some of this

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technology to give us an experimental

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methodology to try to simulate some

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electrochemical systems you might get on

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ocean worlds not just biotic ones but

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also abiotic ones and so as as you all

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know hydrothermal vents are very

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interesting for life and for life's

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origin because they provide chemical

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gradients so things like when the ocean

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has oxidants in it and in modern earth

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it's oxygen but on early Earth you could

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have had things like co2 or ferric iron

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or nitrate so there's a variety of

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possible oxidants you could have and

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this also could vary with space and also

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depending with which planet we're

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talking about and then the rock type and

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the water chemistry will provide you

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with reductants things like maybe

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hydrogen or sulfide or methane and then

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the minerals that precipitate around

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these and when these fluids mix you can

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get precipitation of catalytic minerals

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so things like iron sulphides or iron

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hydroxides or other metal sulfides and

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so it's important to understand you know

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if you're looking for life on an ocean

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world which electron donors and

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acceptors are likely but just because

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you have an electron donor or acceptor

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it doesn't mean that that metabolism

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would be dominant because it also

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depends on how much energy there is but

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also the minerals that are present in

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these systems could affect that so for

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example if you had a mineral on the vent

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that is consuming one of your you know

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favorite electron acceptors that's not

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great because then it's not there for

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life and so we are trying to figure out

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a good experimental system to figure out

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what metabolites are actually going to

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be present and then how can this also

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interplay with a possible prebiotic

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chemist

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and so from we're looking at say Europa

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or Enceladus we don't really know much

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about exactly what the type of vents

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would be and also we have to consider

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these planets over their whole history

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so if you know maybe Enceladus is young

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maybe it's not maybe in the early

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history of Enceladus when it was still

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really actively serpentine izing you

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might have more energy or different

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types of energy than you could have

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today so in an experimental system we

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want to be able to you know have it be

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modular and very these types of things

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but also to isolate individual redox

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reactions and figure out exactly what is

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catalyzing what and which things could

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be linked together so hydrothermal vents

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are sometimes referred to as geo

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chemical fuel cells because in many ways

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they behave like a fuel cell that you

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would see in a battery context they have

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a reductant which comes up from the

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seafloor and if you have a chimney made

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of conductive material electrically

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conductive so stuff like iron minerals

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the electrons if you can oxidize that

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reductant they could flow through that

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mineral and then on the surface of the

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chimney exterior you kind of have this

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electrode situation like a geo electrode

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as we call it where you could maybe

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reduce an oxidant in the seawater so

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this has actually been observed in the

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field and it's been proposed that this

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could also be as something important for

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the origin of life for example if you

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had a co2 rich ocean if you could reduce

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co2 on these geo electrodes you can

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start making organics that way this

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could also work for things like the

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nitrogen species nitrate or nitrite but

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it could also be a mechanism for

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habitability on the ocean worlds so that

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you don't just have to be living off of

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the soluble substrates that come out of

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the vent you could have life that can do

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extracellular electron transfer actually

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taking the electron directly from the

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mineral surface and so the redox

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reactions that could be physically

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linked to power an ecosystem or a

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prebiotic reaction you have to figure

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out which which you know are the two

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sides of the fuel cell and can they be

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electrically linked or not so we've been

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trying to do at JPL this is now getting

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into kind of our just ideas we have for

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the ways you could do such an experiment

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and we hope to find collaborators and

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ideas of how to refine this so if you

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actually were to build a fuel cell to

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simulate event you would want to have

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the hydrothermal fluid which is your

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fuel and you would choose a specific

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reduction to go in

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then you know on the Occident side that

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would represent your ocean and you would

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choose one oxidant to go there and then

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a fuel cell is built at these two

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reservoirs that are connected over a

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membrane and the membranes usually made

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of nafion which is a proton conductor so

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you want to have ion exchange but you

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also want to have each side of the

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membrane coated in a catalyst so in a

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real fuel cell these are things like

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platinum because you're trying to make

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the best battery but in this experiment

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we want to make the catalyst the cathode

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and the anode side represent the kind of

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minerals you would see in the

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geochemical system so basically we want

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to find ways to make geological material

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or analog planetary material into

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electrodes in a fuel cell and then pump

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relevant oxidants and reductants through

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it so in a previous paper we showed that

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this is a possibility so we took a

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sample from a black smoker vent this is

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an iron sulfide and other metal sulphide

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mix and this can be done in general with

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other minerals too so actually you know

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paint is made of mineral particles mixed

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with ethanol or paint thinner right and

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so you can make paint out of any rock or

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that you really want to so we have this

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rock you grind it up really small you

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get very small particles like a few

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micron in size we mix that up with a

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binder you can also add catalysts to it

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if you're not if it's not reacting well

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enough you can put some Navion in there

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so in Figure C there that's the ink that

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we made out of a rock and so that ink

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can then be spray-painted or painted

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with a brush if you like onto the two

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sides of an Avion membrane and you could

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use the same paint for both sides you

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could use two different paints if you

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think the outside and inside of the

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chimney would have different

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compositions so then we put that in the

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fuel cell and then we have two graphic

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plates and one on either side and each

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one is flowing fluid through it one has

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the vent fluid and one has the ocean and

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then we can see if this reacts the same

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way that you observe it in the field so

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for this system we were simulating a

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modern-day black smoker because that's

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whether you get a sample from and so you

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would expect oxygen as an oxidant and

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then in this case it was hydrogen

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sulfide as a reductant and so we

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observed in this hydrothermal fuel cell

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thing that we built that you we were

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actually able to see sulphide oxidation

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which is not super surprising because

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sulfide is very easy to oxidize very

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easy to oxidize but we also observed

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oxygen reduction that was coupled to the

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sulphide oxidation

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and it was driven by the presence of

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these minerals so in a control where we

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had no minerals we didn't observe this

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reaction going so this can show you this

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is a biotic but it can show you that you

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would have these things present and

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either side of the fuel cell could be a

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biotic but it could be a link to a

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biotic system and so now if we're gonna

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think about how to apply this to ocean

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world's it's you know it's always kind

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of theoretical about which exact

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environments we can simulate so now you

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know it gets a little speculative but on

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earth we know that the life life is

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found at pretty much all pressures in

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the ocean that we found there's also

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lots of subsurface life even below that

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so we haven't really found the pressure

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limit of life yet which means that if

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you're looking at a small world like

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Enceladus where the pressure at the sea

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floor is only going to be about 70 bar

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but in Stella toises deep interior it's

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kind of analogous pressure wise to

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Earth's average ocean depth and so

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because life on Earth can live in all

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these pressures if you had Enceladus or

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another planet that had a lot of

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fractures in the subsurface you might

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have life not just at vents but also

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kind of in the rocks below and who knows

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how far deep in the core if the water

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could get in there so we want to

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simulate not just the actual vent but

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the kind of the sediments around it and

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then the rocks and minerals below so

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this is you know a simulation of what

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you might see on Enceladus and possible

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metabolisms that have been proposed so

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for insulative let's say if you're

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having a serpentine izing system that

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makes hydrogen maybe methane

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you could have meth an agenda psious if

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there's co2 but you could also have

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other metabolisms that use that hydrogen

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it's not just with Anna Genesis that's

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possible you could also consume the

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methane with something like say ferric

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iron and so if you have minerals present

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as electrodes that are mixed valence and

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reactive you could actually use those as

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metabolites as well so here's an example

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of the fuel cell and one one funny thing

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that we found originally was that this

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graphite fuel cell was the surface of

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the graphite was really reactive so the

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sulfide was oxidizing but as oxidizing

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all the time and it's because you have

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to make your material choices very you

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know cleverly for this so we have a new

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fuel cell that is a custom-made version

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that's made of plastic and so it's a

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Newark electro chemically but it's also

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not giving us you know fake organic

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signatures so choosing materials here is

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important because the things that you

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would normally pick to make a good fuel

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cell are not what you want for this type

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of experiment so if we have a cathode on

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an O in this case the anode is going to

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be the interior and the cat'll be the

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exterior you could have a chimney

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environment and so life can live in

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chimneys this is great it can kind of

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interface directly with the ocean and so

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we could make simulated chimneys in lab

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you could get samples from things that

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are analogous on earth so that's one

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possibility that we could simulate here

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another possibility is if you have

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plumes and sediments forming in your

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event those sediments can be very

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reactive too so you can get things like

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sulfides hydroxides metal oxides and

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those are great as well for electro

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catalysts so we can either make

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simulated sediments and then make paint

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from that or we can get different types

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of sediments from the field or you can

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go deeper and consider things like say

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chondrite rich rocky core because

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chondrites will have bits of metallic

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iron nickel and meteorite material is

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definitely very electro chemically

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reactive this has been shown in several

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studies so if you imagine the Enceladus

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not quite yet serpentine eyes but also

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pretty chondritic with you know iron

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nickel chondrite stuff in there you

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could get some reactions going on there

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as well and all of this links to make a

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fairly complex abiotic / biotic

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electrochemical system so any of these

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or all of these could be your geo

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catalysts and so the thing to consider

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is that on earth we see a lot of

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examples where biological systems are

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linked physically to something farther

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away so you have a lot of synergy going

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on with different microbial communities

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you can have one say doing redox at like

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the bottom of a sediment column but then

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you have conductive sediment material

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that then connects that physically to

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another colony at the top and so what if

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you had something like this on an ocean

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world where there's one bacteria archaea

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doing something you know at one location

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and then it's connected with minerals

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that are conductive like a wire to some

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abiotic reaction or a prebiotic reaction

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so in that sense maybe the the origin of

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life or the prebiotic stuff that's

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happening is also kind of linked to the

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emerging metabolism it's not all one

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event so an example of a abiotic yet

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pretty organic looking reaction that

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might end up being linked here I

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presented a more detailed version of

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this on Wednesday but you can have for

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example iron hydroxide minerals that

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very catalytic and if you have simple

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organic molecules produced in vents or

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delivered from meteorites those can

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react to give you other stuff like amino

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acids or alpha hydroxy acids and so this

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is a redox reaction driven by a mineral

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that's not biological but would be a

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pretty confusing thing to see if you're

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trying to determine a bio signature and

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so if this could be linked to something

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more biological for example a sulfide

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oxidation by a microbe on let's say a

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metal sulphide or a chondritic type

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surface and that could be electrically

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linked in the fuel cell to something

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that's a biotic or prebiotic so one of

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the one of the technical challenges we

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faced is that you have to be able to

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actually conduct those electrons from

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one side to the other and it's hard when

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the minerals aren't actually touching

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the electrode surface so we've been

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developing different ways to do that and

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one of those is to have this mesh of a

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bimetallic mesh that connects to the

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mineral and then that conducts the

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electrons to the other side and the

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important thing is that when you do this

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in an actual fuel cell you separate the

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two sides of the redox reaction and that

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way you can you can tell exactly which

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half reaction is causing which product

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it as opposed to say a full bottle or

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closed system where you just get

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products out but you might not know what

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exactly is catalyzing what so fuel cells

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can be fairly useful in this regard

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again inert plastic is important because

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when the fuel cell is reactive

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experiments don't make any sense so in

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conclusion you know if we're gonna

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consider hydrothermal redox chemistry on

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other worlds both for the origin of life

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or for life to survive it's not just

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what energy is present it's also how are

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the minerals reacting with those suppose

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that electron donors or acceptors and

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how does it affect their availability

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for life and so this would probably

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requires some modeling as well and an

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understanding you know which prebiotic

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reactions are most favored and could you

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link those together electrochemically

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over what kinds of distances even so for

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in celle tiss-you no possible oxidants

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include lots of interesting things like

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what about sulfate or I don't know

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00:13:10,130 --> 00:13:08,820
nitrous oxide and then possible

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reductants could include things like

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ferrous iron or hydrogen or methane and

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we could do tests in this fuel cell to

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determine you know to differentiate

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between hypotheses of say biogenic

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versions of any of these things that you

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00:13:23,990 --> 00:13:22,500
might eventually see in a plume and by

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the way it is thought that the plume

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00:13:26,600 --> 00:13:25,230
material is

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coming from deeper below just the

401
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seafloor and so if that's the case then

402
00:13:32,090 --> 00:13:30,180
if you have redox stuff going on below

403
00:13:33,500 --> 00:13:32,100
the sea floor and we could simulate that

404
00:13:35,360 --> 00:13:33,510
here we might be able to predict what

405
00:13:37,910 --> 00:13:35,370
how to interpret something from a plume

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00:13:39,680 --> 00:13:37,920
that's a potential bio signature and the

407
00:13:40,910 --> 00:13:39,690
mineral catalyst that might be important

408
00:13:43,130 --> 00:13:40,920
that we're working on right now for

409
00:13:45,200 --> 00:13:43,140
making electrodes include olivine the

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00:13:48,140 --> 00:13:45,210
iron hydroxides the phyllosilicates the

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00:13:50,300 --> 00:13:48,150
chondrites and so on so stay tuned and

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hopefully an in celle de steel cell will

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yield some interesting results and so I

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just want to thank our lab group the JPL

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00:13:58,760 --> 00:13:56,970
origins in habitability lab and in

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00:14:00,920 --> 00:13:58,770
particular our collaborators John Paul

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00:14:02,660 --> 00:14:00,930
Jones and Keith chin so they're the

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00:14:04,130 --> 00:14:02,670
electrochemical technologies group who

419
00:14:06,800 --> 00:14:04,140
are using their battery expertise to

420
00:14:08,510 --> 00:14:06,810
apply it to astrobiology and also Nino's

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00:14:09,560 --> 00:14:08,520
hermus and Erika Flores who the grad

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00:14:11,890 --> 00:14:09,570
students who have helped with these