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thanks to decades of research and

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several missions like curiosity here

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we know today that mars used to be

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habitable in the beginning of its

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history

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it had a dense atmosphere

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a global northern ocean

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rivers and lakes and temperatures

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similar to earth

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but unfortunately four billion years ago

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it lost its magnetic field

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and without this protection the planet

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progressively turned into the freezing

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irradiated desert we know today

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however there is a small window of

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habitability and the big question is

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did life appear before the planet lost

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its magnetic field and did it leave any

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trace we can detect today

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to answer these questions we're sending

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rovers to the red planet

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and both perseverance and the rosalind

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franklin rovers have four main

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objectives to detect traces of ancient

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life

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later in the presentation i'll present

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you one type of these by signatures

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we're looking for

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but here you can quickly see how

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important their detection is so in order

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to know what instruments to use on mars

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where to send them to have a maximum

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chance to find potential signatures we

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need to understand how these clues can

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be degraded over time

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to understand how biosignature degrade

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on mars we use earth as an analog

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here is an example of all the steps that

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could degrade these signatures between

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the organisms living in a paleo basin

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and now first the incorporation into the

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sediments without being degraded or

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eaten

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then the higher pressures and

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temperatures experienced during

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diogenesis

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followed by additional potential

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exposures to water oxygen or

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microorganisms via fractures

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and for the scientists to be able to

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collect and study these samples we need

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them to be closer to the surface which

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once again brings a lot of possible ways

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to erase our traces of ancient life

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but that is for earth and mars has an

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additional powerful destructive agent

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indeed because it's lost its magnetic

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field the martian surface is exposed to

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heavy radiation

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the first type and most abundant are the

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solar energetic particles they are

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absorbed in the very first two

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centimeters of the surface

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the second type are galactic cosmic rays

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they are less frequent but much more

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powerful and penetrate deeper under the

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surface

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up to several meters down according to

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models

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there they will react with the soil and

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produce showers of secondary radiation

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including gamma radiation

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when we look at the depth where these

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rovers are drilling we see that the

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cosmic rays could have an impact on the

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about signatures we're looking for

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so the main question becomes are any

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biosignature left at this depth and

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knowing that would help us determine

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where to send the rovers and what to

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to take in account this radiation

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part of my project is to irradiate

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different types of analog terrestrial

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samples that naturally preserved

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biomarkers

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i'm focusing on cosmic rays because as

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we just saw they're the main ones at the

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depth where the rovers are drilling and

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i use gamma rays as analog because it's

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one of the main degradation products

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when the cosmic rays hit the surface

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for today's presentation i will focus on

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shells samples shells are fossilized mud

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we have the n shell here on the left

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with the physical trace of a leaf and

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the muscle shell on the right with the

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fish

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and amongst a variety of biosignature

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they're both containing typical lipid

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fossils that i will present in a few

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slides not only fossils from the fish

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and the leaves that you can see but also

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from microbial sources that are not

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after a lot of sample preparation here

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are they ready to be irradiated

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they have been packed flame sealed under

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vacuum and the bottom of the tube is

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facing the radiation source

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and this is how they looked like after

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radiation

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they were exposed to a dose equivalent

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to 15 million years on the martian

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surface with gamma rays

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and then we compared the molecular

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fossils content and quantities between

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the controls that haven't been

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irradiated and irradiated samples if we

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don't see any difference it's a good

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sign for the rovers and we can keep

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increasing the dose to higher levels of

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radiation to see where the trend is

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going

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and if we observe a decrease in

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biomarkers content our objective was to

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characterize the rate and compare it in

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different types of samples

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i'm going to focus for this presentation

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on a specific type of biosignatures

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belonging to lipid biomarkers

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the first types are hopets there are

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fossils of hopanoles which are membrane

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lipids found in prokaryotes as you can

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see during diagenesis we are losing

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functional groups but we keep the

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diagnostic hydrocarbon skeleton

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and this structure if found on another

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planet is complex enough to be

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diagnostic of life

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we don't know any way to synthesize this

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abiotically

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the second biomarker are alkanes

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they can be degraded from fatty acids

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here as we can see in this case a simple

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chain of carbon can be formed without

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life so it's not that one molecule alone

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that will give us any information about

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past life but the distribution of

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alkanes in a sample

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if they're mostly long chains or short

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chains or if they have a higher amount

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of even or odd carbon number etc

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and the rovers that we sent on mars have

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the ability to detect these hydrocarbons

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and to answer our questions but we

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first we compared the total organic

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carbon in our samples and spell on the

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left muscle on the right the controls

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here are in blue and the irradiated

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sample in orange

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the arrow bar here represents the

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natural variation of the sample so we

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see that there is no significant change

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here

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so far it's a good sign for the rovers

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but here is what we saw for the

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hydrocarbons

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they increased

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here is only semi-quantitative data this

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is why we don't have any error bars for

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natural variation but at these levels we

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can be confident that the amount of

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hydrocarbon is almost doubling after

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radiation so we decided to look more

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specifically in our targeted biomarkers

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first we looked at the linear alkanes

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and same thing they increased to even

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higher proportions

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after seeing that we were curious in

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their distribution because as i

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mentioned before the distribution is the

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actual signature here

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here are the results with the size of

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the carbon chain on the x-axis

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and we can see that for both samples

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even if the quantities after radiation

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are larger the distribution itself

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doesn't seem to change much we don't

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suddenly have only large or only short

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carbon chains for examples

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so for alkanes the signal is not only

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preserved but increased after radiation

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for hopping's biosignature it is not as

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clear as it was for alkanes same thing

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again our two samples before and after

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radiation and some of the whole pains we

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identified in the samples

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again this is not precise quantification

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so it's hard to make strong conclusions

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but we see different trains

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some stay at the same similar abundances

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here in n-spell this one is decreasing

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by almost half

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and here these last two muscles are

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doubling we don't expect radiation to

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lead to the synthesis of any of these

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because they're very complex but we have

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a few hypotheses for whole pains and

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overall for a hydrocarbon increase after

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radiation

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concerning hope pains most of the

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variation we see could be natural

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variation

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for this we will do additional

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quantitative analysis

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but there are a lot of other molecules

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in the samples that we don't see in our

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runs due to the methods and the

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instrument we used

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one of them are refractory

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macromolecules like kerogen or

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asphaltenes

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here is an example of their very complex

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macro structure making them not

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extractable by our method or visible by

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our instruments

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but under radiation they could break

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down and liberate alkanes propanes or a

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variety of other hydrocarbons

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and even if they don't fully break down

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radiation could liberate pockets of

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adsorbed or occluded hydrocarbons that

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we now can detect

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for this hypothesis we will irradiate

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standards of kerogen and see if anything

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is liberated

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our last hypothesis is that our very

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well-preserved sample still contain

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fresher organics like fatty acids that

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wouldn't be detected in the hydrocarbon

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phase because they are still polar

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but they could be degraded into alkanes

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during exposure to gamma rays we will

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hear irradiate standards of fatty acid

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to see if any hydrocarbon is created

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here is another way to represent our

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hypothesis the total organic carbon here

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in the blue box doesn't change after

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radiation

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then a part of that organic carbon are

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the extractable hydrocarbon that we see

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in our rounds they double in size as you

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can see the green box

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they include the alkanes that were

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increased by a factor of two to almost

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four and the whole panes for which we

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need more

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analysis to be conclusive about

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quantification

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outside the box

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of extractable hydrocarbons we have the

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macromolecules in gray

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that could freeze some hydrocarbons

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under radiation or fatty acids in dark

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blue that could be degraded also into

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hydrocarbons or it could also be a

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complex mix of all these processes

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these counter-intuitive but very

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exciting results opened a whole new plan

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of work to understand what is happening

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to our biomarkers and the radiation

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first we will analyze our samples with

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precise quantitative instruments to

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determine real trends

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then we will re-irradiate the same

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samples but at higher doses to see how

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the trend is evolving the results you

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saw were for 15 million years and as a

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comparison gel crater where curiosity is

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right now has been irradiated for about

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80 million years

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as we mentioned before we will also

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irradiate macromolecules and fatty acid

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standards to figure out if they can

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produce hydrocarbons

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and lastly in this presentation we

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focused on quantifying biomarkers that

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were present in the controls but another

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question would be to know if radiation

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could be creating new types of

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biomarkers that we could look for

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with this i'd like to thank georgetown

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university to johnson's lab and the

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radiation facility at nasa goddard for

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irradiating our samples

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thank you very much for your attention