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[Music]

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[Applause]

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today I'm going to be talking about my

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PhD thesis work so we're sort of

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transitioning now from talking about

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brines and the last few talks to now

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moving on to salts and specifically

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salts and Gale Crater that have been

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measured by the MSL Curiosity rover

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um so from orbit aqueous minerals have

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been mapped extensively on Mars here I'm

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showing the distribution as of 2014

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where Philo silicates clay minerals are

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found throughout the altered noachian

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crustal materials the oldest materials

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and salts are also found but more

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scattered and distribution but they

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provide us important clues to the

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aqueous chemistry of past waters and

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they can also give us more information

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about potential transitions and

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environmental conditions such as

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potentially a global transition to more

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arid climate on Mars which can be sort

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of studied through these salts and also

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can be studied specifically at the

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landing site of MSL curiosity which is

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Gale Crater Gale Crater is a 150

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kilometer diameter crater located at the

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Crystal hemispheric dichotomy boundary

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it's a pretty deep crater this is a

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topographic map which you're looking at

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here and you can see what makes it sort

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of unique compared to the other critters

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in the surrounding area is it has this

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large mound in the center that's Mount

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sharp which is a sedimentary sequence at

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the center of the crater which has been

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mapped extensively from orbit so zooming

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into that white box there work by framin

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at all and others has shown the from the

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base of the mound where we this is where

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we sort of started a methyls Traverse to

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the top of the mound on the bottom right

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we transition from clay mat rich

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materials to sulfate rich materials

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again potentially sort of capturing that

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transition to a more arid climate and

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this can be studied in depth and fit you

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and put together into

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Astra ticker fee so here this is frame

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and it alls strat column showing a

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transition from the lowest layers the

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memory formation these clay rich

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materials to more sulfate rich materials

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which we haven't yet reached to miss the

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rover Curiosity like I said started down

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here on the floor of Gale Crater and

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it's currently in that clay bearing unit

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which I have noted so some of

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curiosity's initial findings when it got

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to Gale is these beautiful fine-grained

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rocks and the Yellowknife Bay Area which

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record information on a long live

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ancient lake and preserve evidence for

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an environment suited to support a

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Martian biosphere founded on key Melissa

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Otto trophy another paper by a separate

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crossing or a tall paper began to study

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the Mount sharp sedimentary sequence we

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first encountered it here at the

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parentals member of the more information

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where these fine finally laminated rocks

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were observed which were consistent with

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deposition and a sub aqueous lake and so

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here the MSL team began putting together

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a strat column and so you're going to be

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seeing many strat columns in this

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presentation so to orient you with them

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this is showing elevation and showing

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all the mapped units within Mount sharp

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so this was our MSL team strat column as

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of 2015 and curiosity is now here so

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we've made it a long way and collected

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many more observations since 2015

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our stratigraphy has expanded

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dramatically as we've continued to climb

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up Mount sharp and explore more layers

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and we've gained thousands and thousands

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more observations and some of the

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information we've gained from the last

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few years is we found new evidence for

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potential oscillations in the lake level

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that are recorded in this murray

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formation so this includes some

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heterolytic sedimentary textures

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defecation cracks varying clay

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chemistry's and

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or eight salts but one of the challenges

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that we face one of the best ways to

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study paleo environment is by looking at

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the mineralogy the challenge here is you

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might observe these black dots on the

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strat column they indicate where MSL

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actually drilled and so got a

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measurement of mineralogy you might

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notice that there's a big gap here and

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that was when the drill of the rover

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wasn't working but there's still lots of

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interesting change environmental changes

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potentially being recorded in these

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rocks and there's still a lot to be

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studied with this within this area so we

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need to use another tool to understand

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these transitions and the tool that I

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used for my PhD thesis is an instrument

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on board curiosity called chemcam

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chemcam is a laser-induced breakdown

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spectroscopy instrument so it performs

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lips and it's very valuable for studying

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salts because it provides a very large

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data set every day curiosity measures a

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few rocks with chemcam totaling to over

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20,000 individual locations measured on

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the surface to date it provides very

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fine scale elemental geochemistry

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measurements so each individual lives

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spots our chemistry measurement is only

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350 to 500 50 microns in diameter and

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volatile elements which allow us to

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measure and quantify salts have week but

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detectable emission lines with chemcam

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so the objective of my work has been to

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map the presence of salts and Gale

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Crater you think that chemcam instrument

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so previously assaults have been

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observed in a few different morphologies

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the first being and most common being

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these calcium sulfate filled veins or

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these fractures we also see magnesium

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sulfates enriched in some of these

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dendrites nodules and ridges of salts

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and clays and also fluorine enriched

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materials my co-author and collaborator

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William Rippon has worked extensively on

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studying salts and Gale Crater as well

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and one of his focuses has been studying

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calcium sulfate

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within the bedrock so in addition to

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those veins that I showed you on the

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last slide we've also seen bedrock

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material enriched in calcium sulfate

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likely indicating pore filling cements

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present within these bedrock so here

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again I'm showing the strat column with

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all the different members of the Murray

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formation and red is where William has

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mapped calcium sulfate enriched bedrock

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such as these cue targets shown here

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Williams also been focusing on another

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type of sulfate magnesium sulfates

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within Gale Crater specifically chemcam

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was able to detect magnesium sulfates in

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the red targets shown on this slide so

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beach cliff and Norwood Cove which

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correspond more rubley Dark Materials so

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there's some thought and some evidence

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that these may be primary magnesium

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sulfate salts my focus on the other hand

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oh and then one worth light so this is a

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sort of summary of Williams work where

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we're looking at the strat column and

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then the locations of the calcium

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sulfates and the locations right here of

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the magnesium sulfate salts and you can

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see that the magnesium sulfates in

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particular are restricted and they're

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stratigraphic position so they only

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occur pretty much in the Sutton Island

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and Blunt's point members so indicating

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a brief transition to it potentially

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different more saline rich fluids so my

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focus have actually been though chloride

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salts within Gale Crater

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so we've observed a bunch of different

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morphologies within the memory formation

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three of them being bedrock this is just

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a classic Murray formation bedrock

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target these nodule rich bedrock targets

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and then also veins and we've actually

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managed to detect chlorine and isolated

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observation points of these targets so

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where you see the red circles on the

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bottom is where chlorine is detected

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within the chemcam observation just as a

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chlorine peak within our spectra and one

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individual observation point of the

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cam cam measurement so indicating that

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we're sort of observing these isolated

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sporadic enrichments potentially of

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chloride salts so here again we're

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looking at our MSL strat column along

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with in the center the apxs measurements

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of chlorine you can see apxs which is

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another chemistry instrument aboard

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Curiosity observes pretty much constant

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chlorine throughout the stratigraphy not

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much variation on the other hand chemcam

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shown on the right plot here which is my

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work you can see there's a lot of

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variation in chlorine and specifically a

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lot of enrichments up here in these

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Sutton Island and blunts point members

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of the Murray formation this is likely

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due to the very difference in

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observation scale of the two instruments

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where chemcam like I said is observing

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these really fine points so we're likely

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targeting individual chlorine rich

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grains or porcelain cements apxs is

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averaging chemistry over a much larger

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area it might not be sensitive to these

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small scale enrichments another

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interesting observation about these

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targets that are chlorine rich are that

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they're also sodium rich so you can see

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that there's a pretty clear correlation

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between sodium and chlorine which

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indicates to us that this is likely a

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sodium chloride salt thank you so we

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also have some supporting evidence that

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the phase were observing is halite

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specifically the chemin instrument that

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mineralogy instrument I mentioned to you

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earlier has measured halite within the

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Kaela drill site which is indicated by

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the orange star and the Sam instrument

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also from Archer at all work showed that

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there was a transition from perchlorate

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rich materials to chloride rich

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materials as we transitioned up to where

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the orange dots are within the Murray

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formation so to wrap this all together

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into a potential and placement scenario

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but we think the sort of combined

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evidence of the sulfate salts and the

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chloride salts that these were first

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deposited potentially via evaporation of

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lake waters as summary formation was

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deposited but later on sulfate rich

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ground waters were prevalent and we

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think there may have been multiple

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sulfate rich groundwater events which

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mostly - completely dissolved the halite

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which is a very mobile phase and

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redeposit the halite as individual

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grains and potentially cements within

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the bedrock explaining sort of it's

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sporadic occurrence throughout the

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murray formation for more information on

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so just to wrap this talk up and give

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you some conclusions

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MSL has identified a variety of salts

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within Gale Crater including calcium

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sulfates and a medium sulfates borates

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and chlorides these salts can help us

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get a better understanding of the

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ancient lake and groundwater

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environments present at Gale and they

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also record fluctuating water levels of

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the lake and also potentially increased

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salinity and certain periods

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specifically where we saw those Sutton

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Island and bluntz point members of the

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Murray formation where there was an

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enrichment and more magnesium sulfates

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and chlorides present more studies

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though are needed to understand how this

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might impact our understanding of gales

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habitability so how does varying or

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alternating saline and fresh waters

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affect microbial communities and also

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how viable are these for our search for

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life since they've been so impacted by

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later groundwater at diagenesis that's

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about all I have thank you

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[Applause]

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jen has a question

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take chairs prerogative how do you know

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that the chlorine you're seeing from

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libs is chloride and not perchlorate

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that's a great question so that's where

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we're relying on evidence from other

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instruments as well so the Sam

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instrument and some recent work by

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Archer at all has given us more

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confidence that this is likely chloride

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we also have some evidence from chemcam

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which points to the fact that this is of

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chloride rather than thirty law right

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which is the fact that we do measure

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oxygen

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variety of phases within the rock and

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also due to atmospheric breakdown so but

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there's no clear correlation with oxygen

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for these targets so we have some

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evidence there they as well thanks to