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[Music]

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hi I'm Eric and this is an ice shelf

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just off the north coast of Ellesmere

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Island in the Canadian Arctic and this

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is interesting for my purposes because

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this ice shelf has relatively extensive

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microbial mats covering it that are

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dominated by cyanobacteria and in

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particular the cyanobacteria have some

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of the highest concentrations of site

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aneema in a pigment that we're going to

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be talking about this is a photo

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protective pigment it absorbs UV

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radiation and helps protect the sign of

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bacterial cells and it makes sense that

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in this kind of environment say the

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bacteria would produce quite a lot of it

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because this is a very exposed

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environment and not only is the sun

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shining from the top but also there's a

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very reflective surface and thus it's

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very hard to escape this this radiation

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as anyone would know who has maybe spent

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some time skiing in the in the spring

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it's very hard to avoid getting

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sunburned so if we look at zoomed in

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pictures of these types of nets we can

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see quite a bit of this this this

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brownish or dark orange pigment which is

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which is what sites and even looks like

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invisible light here is an absorption

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spectrum of sites anemia this is the the

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solid line with an S and you can see

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that it is best at absorbing in the long

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wavelength end of the of the UV spectrum

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so 2 UV a is is where it where it

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absorbs the best and you can also see

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that in the visible light it doesn't

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really absorb anything instead of the

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the yellow and red region that's why it

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white looks yellowish and and reddish in

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their visible lights there is another

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set of compounds that cyanobacteria use

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for the

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you refer to protection they are the

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micros foreign like amino acids and this

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is something that I want to look at in

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future work so when we first started

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looking at this particular compound and

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the history of its biosynthesis one

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thing that that occurred to us is a

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relevant environmental factor that would

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influence the production of site anemia

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in the past is is obviously the oxygen

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level because because in in today's

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world at least it is the ozone layer

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that mostly modulates how much UV

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radiation gets onto the ground and and

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how much the organisms have to deal with

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it and so this is a famous graph by by

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Tim Lyons and others and depicts the the

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oxygen history on earth showing sort of

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two general increases in oxygen level

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one about 2.4 2.3 billion years ago

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referred to as the great oxygenation

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event and one in that in the lake near

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Perth or Zurich about 600 650 million

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years ago and so this clearly would have

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had an influence on the presence of the

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ozone layer because those onus is made

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out of oxygen photochemically so before

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here there will be very little those are

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layer here things would change a bit and

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here you know something close to the

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modern an ozone layer but probably

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appear now this this UVA radiation is

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interesting in that the ozone layer

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doesn't really do much to it to be

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honest but what is interesting about it

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is that this UVA radiation actually

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becomes dangerous to organisms in the

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presence of oxygen because UVA is very

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good at making various reactive oxygen

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radicals that are then injurious to

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living cells so for our purposes

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actually this curve is more relevant as

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a time as a showing when the exactly

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oxygen arose in such a way that perhaps

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now UVA protection would be necessary

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another thing that as children the first

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picture might influence satiny

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mid-levels in organisms is glaciations

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and in particular perhaps the most

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extensive and and then largest ones the

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global they see Asians of the Paleo

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Proterozoic at the neoproterozoic and so

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you know especially in some of the more

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extreme hard snowball scenarios that

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people have proposed you know where you

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have a global sea glacier where all the

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oceans are covered with hundreds of

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meters of water well the central

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questions is how to sustain complex life

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in these systems which which did happen

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and one necessary component for that is

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obviously that someone somewhere needs

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to do photosynthesis and one thing that

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has been proposed is that perhaps there

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were cyanobacteria in enough water ponds

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probably close to the equator and then

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perhaps these environments do not look

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unlike what we see today and in places

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like Ellis Muir Island

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so again if this was the case then

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perhaps we would we would expect to see

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interesting developments in sites and

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even production at at these times and

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then maybe more so than in today's polar

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environments because here we're talking

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about equatorial environments where

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where the intensity of radiation is is

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harsher than then today in the polar

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areas so very briefly saturnine in is is

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this this pigment here it is it is

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synthesized based on relatively

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relatively basic organic compounds

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tryptophan prep inator are some

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precursors and there is the set of of a

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proteins called saya through through CF

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that do most of the synthesis synthesis

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and I'll briefly also be mentioning some

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other proteins that mainly that mainly

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make the precursors for this for this

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synthesis now these relevant genes which

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contain the information for these

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proteins are collected into one cluster

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in the genomes of organisms the

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heather's there there one operon and we

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will be talking most about the yellow

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this is a a phylogenetic tree of one of

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them of saisi it's versions in different

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organisms I don't expect you to be able

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to read the names but I will talk about

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the general structure of this tree

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this shows how this isyes in different

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organisms are related to each other and

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we can see that there is this there is

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this large group of um gnostic Ailey's

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these are certain mostly mostly

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terrestrial cyanobacteria that live in

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large colonies and and if we look

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actually at that this help free or even

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if we look within the star Kaylee's we

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can actually see that this that the

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screen reflects the species tree

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relatively well and even if we look

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beyond the duster Kaylee's we see that

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the closest sister group is this genus

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crawl coccidiosis

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and beyond that we have some some more

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distantly related cyanobacteria this

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basically looks exactly the same as a

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species tree of all above this clade of

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cyanobacteria here we can see the here

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we can see the Noster Kaylee's we can

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see curl coccidiosis the the closest

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sister group in our study as well and

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some of the things so them in the top

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part of the LR tree here are these

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things that our sister - - Gnostic

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aalesunds and curl coccidiosis so

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basically it seems that what has

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happened is that the capacity to produce

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such an amine arose in some common

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ancestor of this clade here and has

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since been vertically inherited by by

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its descendants losted some of them but

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but not not that many of them so so here

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now we this is an existing species creed

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cyanobacteria that was made a few years

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ago many different well conserved genes

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including ribosomal protein irreversible

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protein genes and things like that were

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used for that and so what the reason why

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I wanted to want you to check my tree

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against this is mainly to date when

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exactly sites anemic production would

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have appeared and basically that would

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mean that we would need to determine

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where exactly

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this last common ancestor of the clades

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that have the sight anemia production

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capacity existed and so there's no

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disorder about here so so maybe is

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somewhere between 2.0 and 2.5 billion

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years ago is when when this claim with

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sites and even diverges from from other

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cyanobacteria that do not have site

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anemia below I have a different tree

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which is from the same paper it just

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makes slightly different assumptions

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about molecular evolution rates and uses

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slightly different calibrations and you

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can see that here this relevant relevant

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branching event is prospectus lightly

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slightly more to about two point two

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point find again with with some

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uncertainties as you can see from the

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error bars over here so that's so from

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our study it seems that this is

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something that was developed made

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somewhere between two and two and a half

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billion years ago and and there was very

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recently about about two months ago

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another paper by by people from Arizona

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State University where they also made an

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effort to to date cyanobacteria

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production of sites and even they used a

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different set of genes they actually

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looked at these at these genes that are

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responsible for the production of the

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precursors to the sites and even

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biosynthesis and in the in the orange

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here you can see the dates for origin of

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secondary production that they got from

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looking at different genes they made

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separate molecular clocks for for each

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of these genes and you can see that

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there is quite a bit of variability but

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in general again the placement would be

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somewhere here just above two billion

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years ago I marked that the goe here in

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in blue so this timing is interesting

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not just for four sites at first sight

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and even then for understanding UV

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radiation protection but also

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obviously it says something more

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generally about when Santa bacteria

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developed and when important

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evolutionary events concerning them

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happens so this is this is here a set of

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their estimated from the same molecular

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clocks for the for the time of origin of

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crown group cyanobacteria again quite a

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bit of variation but but the clear

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consensus that this is something that

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happened well before the goe and then

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people have have argued about this quite

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a bit

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so just to recap it does look like the

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relevant biochemical pathway arose about

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two two and a half billion years ago in

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some commonest ancestor of these what

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are today mostly terrestrial

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cyanobacteria

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and has has been vertically inherited

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ever since it's interesting that the

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origin of this pathway coincides well

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with both the great oxygenation event

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and and the Paleozoic glacial events

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that might have been related to that and

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that's interesting because you know

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again if our hypothesis is that this UVA

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sunscreen became necessary upon the

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introduction of oxygen which suddenly

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may you be a dangerous because it made

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these reactive oxygen species that means

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that perhaps this hypothesis agrees with

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our with our dating finally what I would

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say is that the beyond this idea that

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perhaps we have found this correlation

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between the physical environment events

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and the observation of having this site

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an amine biosynthesis pathway we can

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also flip this whole exercise on our

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head and ask if we believe that certain

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diamond production should appear at this

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point in history where oxygen is

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introduced into the Earth's atmosphere

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then we can use our analysis to check

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any molecular clocks or cyanobacteria as

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a whole and we would know that okay this

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this note here where where cyano this

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branch here where cyanobacterial site

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anemic production appears needs to be

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somewhere around the goe

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right and this actually and then this

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actually would would determine quite a

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bit of when various other important

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divergence events inside a bacterial

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history appear and obviously it would

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push the the origin of crown group

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cyanobacteria into the past

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substantially beyond the goe so that's

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all currently and I'm happy to take

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questions thank you

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Oh sue I'm not sure if you highlighted

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this in detail but there bacteria

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archaea prokaryotes a whole host of

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mechanisms to deal with oxidative stress

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so related to this would you see also we

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have none at this point but it is

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definitely something that we want to do

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we want to in fact not only analyze the

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relevant genes for for other ways of

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dealing with oxidative stress their DNA

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repair mechanisms and all these things

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but another approach that we that we

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want to take is also that we're very

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welcome for any suggestions that we

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should in any particular genes or Dean

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families that we should look into for

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anything that might be relevant to the

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to the physical environment that we're

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looking into so if anyone has any

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suggestions about as you pointed out the

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relevant biological process that we're

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looking at and that might be informative

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over the same question or if anyone has

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any suggestions of any gene or gene

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family that might be particularly

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sensitive to perhaps the the snowball

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earth events coinciding with with a goe

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or the sub C or the subsequent near

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further zoic oxygenation event these

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suggestions are very very welcome and we

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in fact see this as a as a step in a

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larger study of of this type a very cool

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talk so I was interested about your

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molecular clock calibration how many

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micro fossils were using to calibrate it

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so again to clarify the molecular clock

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is not mine it is from Bettina cher

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Meister and others from 2015 the I would

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have to look up the exact number the

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number is small and the sign of

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bacterial trees are still dictated by

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the choice of individual calibration

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points the number is on the order of 3 5

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something like that I know that you know

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one that I think definitely is commonly

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used is is the first

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the first sign of bacteria with

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heterocysts so so these sections four

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and four and five here which are which

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is you know this this this here and i

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think this number two might actually

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correspond to one of the calibrations

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that they use but it's it's a small

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number that's why we still argue about

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sign of bacterial timing in history that

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simultaneous evolution of society si

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great question i didn't go into much of

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this sort of phylogenetic detail here

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but it is interesting that all of them

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all of them seem to be present or in

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fact all of them except for like side d

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which is not critical for making such an

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even anyway all of them seem to be

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present in this in this one group and in

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most organisms that have any of these

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they have all of these and he said so it

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does seem that they came in at the same

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time or or maybe maybe if they if they

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came in at first then you know these inc

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uptake pathways have not been preserved

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in terms of where they came from the if

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I recall correctly sigh see inside

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Beaver at least two of them had no

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closer love related genes whatsoever

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that you would find when you blast them

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or something like that so God knows

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there might have been a heart saltine

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transfer from this from an extinct

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lineage could be anything some of the

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others had somewhat closely related

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homologs among scientifically had maybe

378
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some other function before but how this

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campaign together this is this is very

380
00:18:29,940 --> 00:18:27,940
interesting because II do genes they're

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also critical for making sites and even

382
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they seem to be have the other most

383
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closely related things in Bacteroides

384
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again they do its own gene transfer

385
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event from there it's fascinating how