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hi everyone I'm fury and today I'm going

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to take us back into the archaean wall

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we're gonna look into silica isotope

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fractionation during the reductive

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dissolution of I and silica gel and this

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reduction is mediated by an organism

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diesel parameters which is capable of

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iron reduction and before we proceed any

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further I would like to just tank

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uw-madison and also NASA for allowing me

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the opportunity to be a part of this

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study alright if I jump into any details

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I'll just outline give you a brief

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outline of my talk today so first of all

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we're going to look into two papers from

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the literature that served as a

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motivation towards the science silica

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gel study and then we'll move into the

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Precambrian silica cycle and contrast it

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with a modern silica cycle and look at

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the difference and then we'll go into

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some silica shuttup basics looking into

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silica is to abundances Delta silica

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notation well cross it into looking why

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is it that Seleka isotope is an

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important factor in the Precambrian

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record why are people interested why are

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people interested why are people why is

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their interest for silica isotopes in

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the Precambrian record so the first

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example we would look at as the couple

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iron and silica bottle and then we're

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moving to select isotopes in shirts that

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have been particularly used to spill

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your thermometers we'll also go into

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silica isotopes as a sauce tracer we'll

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wrap that up and then we'll move into my

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experimental approach looking into how I

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synthesize the iron silica gel and also

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the artificial arc in seawater which is

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the seawater matrix media here and then

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I'll show you some data will go into the

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iron reduction of this gel over time and

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then we'll move into isotopic data in

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the sense of silica sio2 Berra for the

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equals and solid phase of my samples

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will conclude with some fractionation

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factor over time and what that means to

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us or at least to me at this point all

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right I mentioned earlier that there

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were two papers from the literature that

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sort of motivated the study the first

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paper looked at ionized took

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fractionation of this

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I'm silica gel a co precipitate in an

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aqueous media similar to the akhiyan sea

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water and found that the eye on silica

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gel is of highly reducible nature and

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the silica president this gel leads to

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formation of silica bearing products say

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for example precursor to green elite's

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in banded iron formations that we see

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today and then the second paper also

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looks into ionizer top fractionation but

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looks into ionizer to a fractionation

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between the Equus ferus ion and also I

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and select that gel in an aqueous in an

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aqueous media of seawater composition

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from the akhiyan and found that by

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wearing iron to select our ratio in the

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gel you get different fractionation

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factors so when you have an iron to

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select a ratio that is high you have a

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lesser negative fractionation factor as

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compared to when you have an iron to

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silica ratio which is smaller you see a

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more negative fractionation Factor both

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of these papers look into iron isotope

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fractionation stone but what about the

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silica that's present in this gel so

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what is the silica isotope fractionation

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that you see you in silica is mobilized

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during the similar tree iron reduction

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so that's what we're going to try to

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answer with my research but Before we

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jump into answering this question let's

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sorry about that so I mentioned earlier

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that we're going to look into the

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Precambrian and also the modern silica

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cycle as we have seen from the previous

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talks one of the major difference

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between the Precambrian in modern psyche

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silica cycle is the presence of biology

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so in the Precambrian there was no

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biology there was no Psilakis recruiting

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organisms present therefore there was a

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high concentration of silica in ocean

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juarez so precipitation of amorphous

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silica in sedimentary is in beast in

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juarez was possible and that led and

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that is evidence of the church that we

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see today some silica isotope basics so

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that tree stable silica isotopes with 28

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Seleka being the most abundant one and

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30 silica being lease abandon Delta

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silica notation is presented in the

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traditional primal notation so tight so

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tops in the Precambrian record why is it

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of any interest so the first model here

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is the iron and silica cycle model that

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was proposed by Fisher and canal so they

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proposed that in the forex zone where

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anoxic photosynthesis takes place you

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have ferrous ion which gets oxidized

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into ferric hydroxide and then the

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silica dioxide in ocean waters that has

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a high affinity to sort to ferric

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hydroxide once the sorption takes place

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the ferric hydroxide then seems to both

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bottom water and undergoes reductive

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dissolution with reductive the solution

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we have a first component of hot iron

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and we have the silica dioxide that can

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then combine and form iron silicates

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again we see iron silicates are

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precursors to minerals that we see in

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banded iron formations today moving on

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selita isotopes have also been utilized

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as paleo tomorrow mirrors from the

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Precambrian record for example robert

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inchasa don used the correlation between

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delta 18 oxygen and alpha perestroika to

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actually trace the temperatures of ocean

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waters back to the archaean the next

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example of silica isotopes from the

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Precambrian record would be as a sauce

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tracer as we can see here that there are

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two different types of kids based on the

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atomic composition one is the ass shirts

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and the other as the secrets the ass

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shirts is said to be from silica

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saturated seawater that has been

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continuously been sillas continuously

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responsible for solicitation and the

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second one is chemical church which

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represents a mixing gradient between the

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hydrothermal inputs in seawater we've

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seen that selected isotopes is affected

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or controlled by temperature sauces but

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what about the processes that affect

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them what about biology that's where my

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experimental approach comes in so we

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have the iron select our gel and the

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artificial I can see water representing

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the seawater composition of the art kid

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so for the iron silica gel I use tree of

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the ingredients above allowed them to

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make sweet open atmosphere for about two

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weeks on a shaker once the acid

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extraction accounts for about ninety

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five percent of the ferric component to

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total iron that is in close

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representation of

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the I entry phases that might have been

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present in the arc en environment and

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then for the unofficial akhiyan sea

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water is just a recipe modified from the

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first motivational paper that I showed

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you guys it's basically made to be an

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opposite and low in sulphate content and

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we did not introduce any selecta in this

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equal space because we didn't want any

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of the minus signal released by the

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microbes to be blocked when we analyzed

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it for silica isotopes these sulfur a

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minus is the organism of choice in our

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experiment and the reason being saw is

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because the sulfur a minus is the marine

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cousins of geobacter which have been

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recognized for iron reduction and

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previous studies in the literature

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proven that they are capable of reducing

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very component ferric iron in components

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which contains silica also so those are

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my experimental while as you can see

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from day one I have four experimental

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vial to Wiles contains cells of diesel

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for Ramona's while two other wiles

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adjust the gel and the artificial

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audience seawater at day 30 it becomes

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really obvious to us that which wire's

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contains cells and which world are the

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control experiments you can see the

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alright so as I've mentioned earlier the

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coloration difference are the first two

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vials so they transform from being

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yellow to a little bit of that greenish

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that is the vowels with the cells that

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shows us that the ferric component in

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the gel has been reduced to ferrous

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component has been reduced to the

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fairest component and in the control

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experiment since there were no cells of

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the sulfur a minus the coloration

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remained the theme and there was no

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presence of ferrous iron or there might

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have been very insignificant amounts of

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ferrous iron from the initial iron

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silica gel this is the iron reduction

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vera for the iron silica gel over time

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and as you can see corresponding with

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the coloration from the first two

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vessels someone and sell to you can see

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that the reduction increases in that

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sells the reduction is at about sixty to

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seventy percent over a period of seven

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tds as for the control experiment the

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ferrous iron presence is insignificant

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it's about two to three percent and it

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remains stable it doesn't fluctuate much

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so that shows us that reduction hasn't

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alright this is the silica isotope data

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for the aqueous phase in the solid phase

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for my samples the general take away

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from those two plots would be for the

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APIs face you see an enrichment in Delta

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that is silica but for the solids you

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see a depletion in Delta that is so like

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that but the other thing that you want

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to take away from those plots is when

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you look at the aqueous phase you can

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see that the enrichment for Delta that

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is silica for the sole experiment is

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slightly higher than that of the control

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experiment and that tells you that

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ferrous iron presence of ferrous ion is

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causing that difference with the solid

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with the equus and solid data for the

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select isotopes we can actually

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calculate the fractionation factor our

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time and those are the numbers that I've

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came up with so I'd like to point out

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that for the cell experiment you see a

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larger fractionation factor as compared

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to the control experiment and again that

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is due to the presence of ferrous ion in

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the cell experiment and the absence of

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ferrous ion in the control experiment

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therefore we can conclude that first

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iron when it's produced by

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dissolution of the science select a gel

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causes a larger fractionation factor as

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compared to a vessel with no ferrous ion

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or minimal ferrous ion and the isotopic

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fractionation here is probably not

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controlled by biology but the magnitude

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of this fractionation is more attributed

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towards the absence or presence of

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ferrous ion therefore it's not only

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temperature or sauces that's an

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influence towards silica isotopes but

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okie dokie we have time for a few quick

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questions um do you have any idea out

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how easy it would be to find evidence

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for the sort of increased fractionation

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in the actual fossil record that's all

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in the actual fossil record mmm yeah

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looking at actual Iron Man informations

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would this be something that would

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survive that long I know Andy chaya this

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person has looked into fossil records in

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the Precambrian but I don't necessarily