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and so I gave this talk last year but

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now with a thousand percent more results

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in conclusions so yes this is the

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potential photochemical origins of

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banded iron formations I'm Parker

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casselberry at ASU so first banded iron

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formations there are large sedimentary

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deposits of iron oxide by large I mean

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trillions of tons these are laser these

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are very pretty ones in Western

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Australia and they're alternating layers

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of high iron and low iron minerals and

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they're thought to be formed by oxygen

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oxidizing iron in seawater that

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precipitates and the thought for this

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comes from if you look at oxygen levels

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in the atmosphere over time and biff

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relative abundance they correlate well

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there's a lot of this deposited right

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around the great oxidation event but

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there are some alternatives proposed

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there's photo Pharaoh trophy which is a

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biological process it's type of an

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oxygen acronis asst that directly

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oxidizes iron and experiments and

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modeling have shown that you could

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generate enough oxidized iron to make

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Biff's with this and that is a beautiful

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lake where photo photography is studied

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but there's another idea that is

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photooxidation this is a completely

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abiotic process and it's ultraviolet

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light turning iron 2 into iron 3 and

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this is a cartoon I have somewhat

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abstracted mechanistic details so you

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have an ultraviolet photon from the Sun

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hits an iron two species in sea water

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turns it into iron hydroxide and then

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that will precipitate soluble and then

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over time that is transformed into Biff

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minerals like hematite and magnetite and

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the implication here is that as I said

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this is an a

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biotic process so you don't need oxygen

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or even biological activity so are these

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bits that we're seeing really signs of

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oxygen in our life or neither so

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previous work has been done testing this

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in 1983 brighter min at all used a

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mercury lamp and they observed reactions

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using filters for long wavelengths over

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400 nanometers that's in the visible not

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even in the UV so that led them to

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believe that this iron species feo h+

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was responsible because it has

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absorbance going out to almost 450

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nanometers and this is important because

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so this is the solar radiation spectrum

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and here's the UV so the earth had no

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ozone back then so it was somewhat

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proximate to this top of atmosphere

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spectrum there and so if you have feo h+

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it absorbs a huge region of UV and

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getting into the visible where there's a

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lot more radiation as one of my

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professor said that's the meaty part of

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the solar spectrum and Francois took

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these results ran with them and made

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notion model calculated a mass

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cumulation rate and he got about an

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order of magnitude more than an

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estimated natural rate for a bit so that

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led people to conclude this is plausible

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but I went back to re-examine this so I

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used a quartz reactor with ports for

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flowing gas inventing drawing samples

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continuously purged with nitrogen co2

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gas which 2% co2 is not unreasonable for

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the archaean and that's to keep oxygen

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out because this is extremely sensitive

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doxygen solution was deoxygenated di

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water sodium chloride iron and

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bicarbonate so this is what I saw

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24 hours and in the bottom there are

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those kind of orange precipitates Raman

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spectroscopy identified those as lipid

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ocurro site which is consistent with the

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earlier work so then though well the

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mercury lamp poorly matches the solar

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spectrum it has all these peaks and so I

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used a solar simulator as a light source

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which is a Zeon arc lamp and special

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filters to match the solar spectrum but

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if you feo h+ is absorbing then i should

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observe a reaction so this is the dark

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control no precipitation this iron was

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measured on quadrupole icp-ms and

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everything was ratio to sodium to

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correct for any evaporation because

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these experiments took days and dramatic

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pause solar simulator also showed

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nothing no reaction over 46 hours this

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was quite puzzling but the mercury lamp

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and the solar simulator have extremely

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different spectra so there's just a few

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slight differences so what I did is to

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test the wavelength dependence you know

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which of these differences is important

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I performed an experiment using the

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mercury lamp and light filters it was

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one continuous experiment and

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periodically swapping out light filters

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and so if I change light filters and saw

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a reaction oh that's the wavelength that

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caused it so to begin I started with no

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light dark control and so I know our

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precipitation okay good and then light

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longer than 400 nanometers also showed

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no effect this is different than what

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Khan house are observed or

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not seem brighter Minh there's another

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paper con Howser that does agree with

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this and then light longer than three

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hundred and forty five nanometers also

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showed no effect so that is getting down

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into the UV and then boom 295 2 340 5

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nanometers cause significant iron

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precipitation in a couple days and then

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the full spectrum didn't actually show

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an increased rate so I can conclude oh

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and precipitation stopped when the light

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was turned off just to make sure so I

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can conclude that mid UV so 345

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nanometers or so is what's causing this

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reaction and then so what I did is using

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this new wavelength dependence that I

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found I went back to the old models

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where you calculated it using only that

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region that I observed and not the

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long-wavelength where you have all of

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the higher solar radiation and I

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calculated rates that are 6 250 4

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milligrams of iron per square centimeter

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per year depending on the concentration

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of iron too there's a lot of

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uncertainties and assumptions that went

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into this but that's just to get kind of

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a rough estimate and like i said i'm

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missing the longer wave absorbance here

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so this is five times less than previous

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models five times slower but it actually

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still compares favorably to estimated

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natural rates but looking at I talked

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about those alternative theories like

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photo Farrah trophy foto para trophy

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there's actually you can get numbers of

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around 500 milligrams per centimeter per

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year for similar iron concentrations

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so I can conclude here that I

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reevaluated iron photooxidation and

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found it sensitive to wavelengths

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between 295 and 345 nanometers it

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results in photooxidation rates 56 times

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slower for a predicted model and so if

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photo Farrah trophy was around or like

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oxygen for moxa net photosynthesis that

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would likely outpace this process but

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this still is possible in the absence of

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any biology at all so questions actually

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I have some time so I can talk a little

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bit about future work I said I had

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dissolved carbonate in there another

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thing I've been wanting to test

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different additives to this thing's have

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redox interactions with the iron also

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the effects of dissolved organic carbon

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because I could see a photo reduction

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which is what happens a lot in modern

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systems so I might actually get some

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filtered sea water and do experiments

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with that and then after this there's

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other things I could look at

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and I do have time for questions okay

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didn't even have to ask so I had a

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question about your relative xenon arc

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lamp and it's mercury so um I mean xenon

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arc lamps have a lot of output in that

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same near UV range that you're you're

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looking at so what is the like wattage

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of your various lamps like is it just

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coming from a difference there cuz if

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you look at the spectra using it on our

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referring to here yeah yeah um the

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wattage it was 300 watts okay I mean mu

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I guess my question is um the xenon arc

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lamps you know have a lot of energy in

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that range too so maybe it's just a

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power issue with why you weren't seeing

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it it's a power issue um I also I have

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ideas the air mass filter that I put on

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this because that corrects for more of

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the longer wavelengths that I was

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yeah is actually having some absorbance

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right in this region cutting down on the

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xenon arc spectrum so essentially the

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air mass filter for a solar simulator

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might not actually be the best solar

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simulator for these UV wavelengths but

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yeah I'm thinking about doing that also

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00:12:03,040 --> 00:11:57,800
talked about getting a deuterium arc

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lamp for a I guess consistent UV

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00:12:11,210 --> 00:12:08,500
spectrum longer wave or shorter wave but

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yes

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I was wondering so the solar spectrum

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that you're showing here is this for

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acquiescence Sun or like a flaring Sun

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or this is my solar simulator right

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00:12:28,980 --> 00:12:24,700
right but it's supposed to simulate

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00:12:31,800 --> 00:12:28,990
aqueous and yes fun okay i guess i'm

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just wondering since you know the Sun

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does his evolution that is one of my

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favorite questions there we go so here

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is the evolution of the solar spectrum

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and while the solar simulator didn't

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take this into account I actually took

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this into account in my models but the

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Sun was in 20 25 30 percent fainter

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early in its history so this is photon

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flux and the black is the modern

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spectrum and then these are different

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ages for the Sun so 100 million years

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700 million years and 2 billion years

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old and the interesting thing is that

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because I heard a lot of theories well

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the Sun was brighter in the UV but

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actually that is true but only for

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wavelengths under 200 nanometers which

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aren't of interest for this reaction so

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they're generated by different processes

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so does that answer question i think i'm

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referring more to the solar cycle so oh

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I thinks i see i see how you get on

243
00:14:08,030 --> 00:14:06,440
more questions so given the timing of

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00:14:10,550 --> 00:14:08,040
biff deposits that we see in the rock

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00:14:13,070 --> 00:14:10,560
record how much of a contribution do you

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00:14:14,630 --> 00:14:13,080
think this photo-oxidation had on those

247
00:14:24,350 --> 00:14:14,640
formation of you know real world

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00:14:30,970 --> 00:14:24,360
deposits right actually as i scroll back

249
00:14:34,190 --> 00:14:30,980
through all my slides yeah so I mean

250
00:14:41,140 --> 00:14:34,200
what i think is entirely possible is

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00:14:44,030 --> 00:14:41,150
that things like older Biff's here were

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00:14:47,810 --> 00:14:44,040
deposited by photochemistry and then if

253
00:14:50,720 --> 00:14:47,820
at some point photo farah trophy evolved

254
00:14:54,110 --> 00:14:50,730
or accidental photosynthesis then that

255
00:14:55,850 --> 00:14:54,120
is what caused this huge increase so

256
00:14:58,580 --> 00:14:55,860
there might be some background of

257
00:15:11,570 --> 00:14:58,590
photochemistry and then on top of that a

258
00:15:13,400 --> 00:15:11,580
large biogenic signal okay i am not at

259
00:15:14,990 --> 00:15:13,410
all very familiar with photo chemistry

260
00:15:18,140 --> 00:15:15,000
so I have a very basic question for you

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00:15:20,840 --> 00:15:18,150
um in foot in the photooxidation of the

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00:15:24,470 --> 00:15:20,850
reduced iron where is the oxygen coming

263
00:15:27,080 --> 00:15:24,480
from the oxen oh so you're saying is it

264
00:15:29,570 --> 00:15:27,090
like dissolved carbonate that oxygen

265
00:15:33,890 --> 00:15:29,580
yeah that oxygen come from water

266
00:15:35,900 --> 00:15:33,900
actually the oxidized iron takes a

267
00:15:49,770 --> 00:15:35,910
nearby water molecule and is like gimme

268
00:15:57,190 --> 00:15:55,930
so since the UM oh um the OA chums from

269
00:16:02,020 --> 00:15:57,200
the water don't you get a build up of

270
00:16:05,530 --> 00:16:02,030
hydrogen gas that's reducing well you

271
00:16:08,500 --> 00:16:05,540
get hydrogen gas yes but actually this

272
00:16:10,600 --> 00:16:08,510
is in the ocean and it actually escaped

273
00:16:13,870 --> 00:16:10,610
and goes into the app so in your setup

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00:16:15,880 --> 00:16:13,880
it's not an ocean it's smaller so what

275
00:16:17,890 --> 00:16:15,890
what does what do you do with the

276
00:16:19,960 --> 00:16:17,900
hydrogen nuts well I'm continuously

277
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flowing gas through my experiment oh so

278
00:16:26,170 --> 00:16:22,400
there's an in and out yes oh um in fact

279
00:16:28,690 --> 00:16:26,180
I didn't talk about it but I didn't talk

280
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about a gas flow rate but i'm actually

281
00:16:34,870 --> 00:16:31,640
at 500 milliliters per minute I have a

282
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huge doer of liquid nitrogen to keep

283
00:16:39,640 --> 00:16:37,310
this experiment going okay I have tried

284
00:16:43,300 --> 00:16:39,650
lower flow rates but oxygen actually

285
00:16:46,720 --> 00:16:43,310
defuses in because a few i calculated a

286
00:16:49,470 --> 00:16:46,730
few ppm oxygen will give me oxidation

287
00:16:55,540 --> 00:16:49,480
rates that I observed with the lights

288
00:16:59,520 --> 00:16:55,550
okay so um just maybe this may be a

289
00:17:01,960 --> 00:16:59,530
mother geological question along it so

290
00:17:03,730 --> 00:17:01,970
due to the fact I guess there's certain

291
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period of time where parts of the rocky

292
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mountains were actually underwater so is

293
00:17:10,150 --> 00:17:06,770
this actually how they're getting the

294
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the the bands on certain rock formations

295
00:17:20,440 --> 00:17:14,530
that are actually are on land today hmm

296
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but I mean yeah I'm not sure about