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[Music]

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thank you my name is hannah miller i am

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here at cu working with alexis templeton

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so we've already talked about

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serpentinization a little bit but i'm

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going to go into a little bit more

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detail to the actual

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geochemical reaction right here

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so serpentinization is a water rock

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reaction in which you get the oxidation

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of

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mantle

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rocks and minerals such as olivine which

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i show in this equation so olivine has

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this iron two in it when it reacts with

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water in an anoxic environment it

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generates magnesium bearing minerals

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such as serpentine and brucite along

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with

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oxidized minerals like magnetite here

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and hydrogen gas

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and this reaction has been very well

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studied at high temperatures that

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hydrothermal vents are spreading ocean

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or spreading ridges under the ocean but

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it hasn't been well characterized at low

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temperatures

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celsius where life can actually be

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actively harnessing that hydrogen being

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generated from these reactions

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this is an image of what a partially

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serpentized rock looks like so you can

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see why it's called serpentine because

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it generates these veins that look kind

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so what we always talk about how does

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this relate back to astrobiology

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both

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well mars we definitely know has olivine

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mineral olivine minerals on it as well

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as serpentine minerals so there's

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potential that these

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water rock reactions could be occurring

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on mars making hydrogen gas which is an

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electron donor for organisms to be

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utilizing

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additionally europa might also contain

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some of these

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rocks that could be subpoenaizing and

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also studies have been done on enceladus

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and how there might be high ph fluids

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there that indicate serpentinization is

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occurring

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so there are several metabolisms that

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could be supported by these water rock

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reactions one that is oftentimes invoked

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is methanogenesis because if you have

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all this hydrogen around if you if

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there's some carbon available you can

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make methane gas and methane is a

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prevalent gas to be found in these

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serpentinizing environments is source is

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oftentimes debated it may be biotic

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abiotic a mixture of the two but it's

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definitely a relevant gas along with

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hydrogen in these environments

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additionally we know we have all we have

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this electron donor hydrogen around but

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you need electron acceptors two for

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organisms oftentimes nitrate and sulfate

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are found in these environments so you

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can also have various metabolisms that

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utilize those

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one potential exciting metabolism would

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be anaerobic methane oxidation occurring

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in these environments

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so you can see that serpentinization can

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fuel a variety of life and that's kind

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of the theme of the rock powered life

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nasa astrobiology institute which alexis

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templeton heads up here at cu so we are

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really investigating this and a lot of

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different people at the conference have

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been talking about various things that

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rpl is working on

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so i'm specifically working in oman

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which is

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located right here on the eastern edge

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of the arabian peninsula

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and

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oman is a great place to study

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serpentinization because it's the

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world's largest and best exposed

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ophelite sequence and for you

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non-geologists out there an ophiolite

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sequence contains layers of upper mantle

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so if you think about the earth as an

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avocado

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you have your mantle right here so an

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ophelite would be this upper mantle

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which is the green fleshy part of the

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avocado which is actually very

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appropriate because peridotite is a

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beautiful green color because of all

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this reduced iron

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and then you have layered gabbros and

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pillar basalts on top

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but i'm really interested in this

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peridotite right here in oman and

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the opioid was originally

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at a spreading ridge on the ocean floor

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so it's already partially altered by the

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time we study it in oman it's already

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partially sepanized some of that iron

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has already been oxidized

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so i i work on water rock reactions to

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actually characterize how hydrogen is

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being produced in these low temperature

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reactions so first of all we take some

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rock from oman you can see it has a

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beautiful oxidized weathering rind on

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the outside we cut that off because

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we're just interested in looking at this

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relatively unoxidized iron and then we

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go through this arduous process of

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grinding it up into really small pieces

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so there's higher surface area and these

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reactions actually proceed on the level

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of a phd time scale

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and

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into these anaerobic vials we add some

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water of various compositions some that

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simulate seawater or simulate the

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groundwater in the area and then we

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purge the headspace with a nitrogen and

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co2 gas mixture so that there's no

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oxygen in there and these the iron can

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oxidize

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without oxygen around

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and the results we see so i did these

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reactions with this partially

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subpoenaized rock from oman at 100

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degrees celsius

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and this is showing hydrogen production

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right here the two different colors

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indicate

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the rock was reacting with two different

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see what with two different water

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compositions i'm not really going to go

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into that but you get different hydrogen

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production based off of the media

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composition you're reacting the rock

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with but you can see that we generate

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hydrogen up to about 500 animals per

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gram of mineral reactant which is

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actually quite significant for a

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temperature of 100 degrees celsius it's

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one of the highest rate highest

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concentrations reported in the

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literature

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and it's also important to note that

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it's sustained hydrogen production it

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doesn't make hydrogen for one day and

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then just stop it's actually sustained

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so there's a chance a microbe could

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actually be using that hydrogen over

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time

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additionally we look at the aqueous

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chemistry during these reactions and we

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can see that there's an increase in ph

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to about ph 9 after just 24 hours of

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reaction

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and that aligns with what you see in

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serpentinizing environments they have

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high ph's usually they go up to ph 11.

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so we don't see that in the time scales

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of our reactions but it's probably just

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because

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this low temperature reaction isn't

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actually in equilibrium right now

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additionally we see the loss of

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magnesium iron and manganese ions

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initially during the reaction

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so there must be some mineral phase

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that's dissolving

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and we add co2 to the head space as i

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noted that also gets drawn down pretty

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immediately

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and when we see that co2 get drawn down

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we also see a formation of formate and

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acetate

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these

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see just what their formulas are right

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here but this likely forms through this

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reaction right here you have hydrogen

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combining with some of that co2 that's

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dissolved in the fluid to make formate

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the fact that we have acetate is a

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little bit

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interesting and enigmatic because it's a

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lot more complicated to form acetate

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than formate

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but this is still an interesting result

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that we found through these water rock

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reactions

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additionally we also really want to

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characterize the mineralogy during these

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water rock reactions to see how the iron

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is actually oxidizing and what are the

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different reservoirs

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of iron in the system

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so first this is a

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picture of a thin section from ramen

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micro microscopy

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and these yellow blobs here olivine and

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then the light blue in the background is

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all serpentine and this is just a big

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like chromite diopside thing

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but

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we can see that before this rock reacts

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we have serpentine so this rock is

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already reacted we can see it's a

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partially subpoenaized rock but when we

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look at the serpentine right here this

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is the fingerprint region in raman so

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these are the characteristic serpentine

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peaks but when we look at the oh the od

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the oh stretch of the serpentine we see

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this bump right here that corresponds to

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brucite so we can see that bruceite is

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intimately intermixed with this

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serpentine and based off of the peak of

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this bruce site

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we've calibrated how much iron is

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present in the brew site so we can see

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there's 15 weight percent iron present

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and that's important because this could

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be an important source of iron that

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could be oxidizing and leading to

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hydrogen generation

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so when we look at the

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the grains that have reacted and formed

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hydrogen these are some powder xod

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spectrum spectra and you can see

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that right here red

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is the unreacted rock and there's a

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bunch of olivine and serpentine peaks

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but the peak i'm going to focus on this

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one right here this black bump right

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here is bruceite so you can see in the

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unreacted rock there's a fair amount of

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bruceite but then when we act when we

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react the rock with various medias we

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can see that that brewsight peak

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disappears so bruceite is being consumed

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during these water rock reactions

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and that's likely why we saw that

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release of magnesium manganese and iron

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in the aqueous chemistry

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and we also know that brucite contains

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iron so that's a very likely source of

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the iron ii that's been leading to

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hydrogen generation as it gets oxidized

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additionally we've seen

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these are some images of just the thin

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sections of the rock before and after

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reaction so you can see all these little

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splotches of mineral that are forming

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there's definitely serpentine formation

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during these reactions it's very

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amorphous and white and there's not that

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much of it

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but that is important because we know

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from that initial reaction i showed you

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serpentine should be forming

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at these high temperatures we know it

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definitely does but it also does at low

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temperatures

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additionally we use magnetic

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susceptibility methods to show that

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magnetite forms and that's also

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important to note because at these high

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temperatures magnetite is

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thermodynamically expected to form but

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at lower temperatures it hasn't been

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observed as much but we definitely see

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that magnetite is forming and likely

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that's what's accommodating this iron

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okay

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so overall why we think we want to

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propose some sort of reaction for this

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low temperature serpentinization and we

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believe that the dissolution of iron ii

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bearing bruce site is leading to

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hydrogen generation at these low

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temperatures so because this rock was

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already partially sepantonized

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there are some thoughts well is it even

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00:10:08,710 --> 00:10:06,160
still reacted is it reactive is there

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still iron two available for oxidation

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and yes there is and we think a lot of

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that iron too is coming out of brucite

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additionally these reactions can make up

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to 37 nanomoles of hydrogen so this is

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the hydrogen that's dissolved in the

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fluid the hydrogen that's more

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00:10:26,870 --> 00:10:24,079
biologically available

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and that's more than enough to support

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some sort of microorganism because

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methanogens require much lower levels

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than that

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additionally these reactions make

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reduced energy sources such as formating

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acetate which can support support

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fermenters living in the

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so overall that's how we think that low

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temperature hydrogen generation is

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happening in oman of course it's very

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site-specific because these minerals had

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a lot of brewside in them

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i would like to thank everyone in my lab

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and our collaborators and i would like

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to take any questions

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[Applause]

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i was just curious what the average

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ratio of supreme tonight to prototype

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that you had for your samples

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00:11:34,470 --> 00:11:31,200
it started off as about 50 serpentine

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00:11:35,750 --> 00:11:34,480
and 50 um olivine

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was that your question like the mineral

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proportions and

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during the reaction it barely changes

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so just a little bit of blue site we

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think it's about five percent by mass

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00:11:50,470 --> 00:11:46,480
brucite reacted to generate the hydrogen