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you get to hear me talk all over again

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but this time about early is geobiology

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the topic of today's session so first

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off I want to talk about what we mean by

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the early is so this is a diagram of the

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time scale of the entire Earth

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everything that's ever happened and and

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when we say early Earth and geology in

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geobiology what we really mean is pretty

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much everything that happens from here

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where the earth is formed really right

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up to about here which is where

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multicellular life really starts to take

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off so you can also think of it as

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everything that happens before the great

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oxidation event and the ikea and had ian

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but everything that happens in the

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proterozoic is generally included too so

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essentially the early Earth geology that

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sounds like not a lot of its history

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right but we're actually thinking about

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3.5 or four billion years of this four

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and a half billion year history so this

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is clearly a lot of territory to cover

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so what about geobiology well and its

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simplest form geology is where geology

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meets biology in terms of geology what

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we do is we look at rocks and we want to

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know what can they tell us about life in

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the past so this picture up here this is

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a picture of a formation known as the

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gunflint shirt and it's really important

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it was discovered in the 60s because all

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these things here you think wow that

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really looks like a close-up on a

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microscope photo / microbial mat and

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you'd be right this is a 1.9 belen

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year-old microbial med so right away

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this rock is telling us something about

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the organisms that were living 1.9

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billion years ago but there's another

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part to geobiology and that is asking

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what life in the prison can tell us

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about the rot record so this picture

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this is of a stromatolite which some of

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you have probably heard of their

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structures found in the rock record that

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we think indicate microbial life but

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this stromatolite is really cool because

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this stromatolite isn't to the lean

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years old this stromatolite was found in

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a yellow stone hot spring about five six

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years ago that it looks exactly like a

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whole bunch of strata lights from the

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rock record so by studying things like

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this that exists in the prison day we

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can understand

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what the structure that structures in

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the rock record actually are and what

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might have been going on back then so

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let's just go back to this kind of

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diagram of the time scale of the earth

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for a minute and I want to go through

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some of the key events in early Earth

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history to give you a good idea of what

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was going on at different times and the

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kinds of topics that our speakers today

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we'll be talking about so we really kick

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off in terms of geobiology roughly four

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billion years ago which is when the

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oldest known rocks that we can access

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some were being formed so anything that

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happened before four billion years ago

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we don't know about from the rock record

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on earth because those rocks aren't

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there anymore dig on about 3.5 billion

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years ago at the oldest stromatolite so

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oldest probably microbially formed

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structures so that's the first point of

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which we can look at on these things and

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say this is probably life and we're

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seeing evidence already in the rock

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record as a structure just not in terms

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of our predictions about 2.3 million

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years ago came the great oxygen

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oxygenation of in and this is when we

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can say okay there's not just life on

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the planet it's creating so much oxygen

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that it's getting into the atmosphere

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and fundamentally changing how our

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planet is this is the point in which the

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early Earth changes from being in a

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primarily anaerobic world to a not as

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arabic world as today as we were told

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about last night but still a world where

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oxygen is playing a major chemical role

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so this is a really crucial change over

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in our early Earth time period about 1.9

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billion years ago that's the gunflint

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should I was showing you this is when we

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have the oldest microfossils so we can

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undo min on a rock and actually see

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organisms preserved in the rock it's

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also when we have the oldest eukaryote

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fossil so we don't just have prokaryotes

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we've got eukaryotes and we have

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evidence of them about 1.2 billion years

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ago we have the oldest identifiable

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fossils and what I mean by that a

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fossils where we can look at them and

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say in the case of these particular

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fossils these are red algae so we're not

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just saying these are microorganisms

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these are members of the clave that

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exists today that we know about but I'm

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half billion years ago so that's 600

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million years ago we have the oldest

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multicellular fossils and I'm going to

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zoom in a bit on the time scale just to

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bring you up to speed

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on where we hit the modern period and so

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this has really really zoomed in but

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this is this is everything going back to

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600 million years so this is the

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dinosaurs this is us and it's a tiny

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fraction of the whole history of the

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earth so about 600 million years ago we

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have spanish fossils that when you spot

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alive sponges what you most again at

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least tiny little silica glass spec you

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look like a whole sponge but the

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evidence that some silica forming

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sponges were around that 550 million

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years ago maybe 600 to get small Shelly

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fossils and these are the first

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organisms that were forming actual

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shells and then you get the Cambrian

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explosion or the major animal phyla

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appear in the rock record and we're off

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to the races with multicellular life but

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what we really care about is the first

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three and a half four billion years

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before that when multicellular life

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wasn't around so when you don't have

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fossils in the rock record when you

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don't have your bones and your

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coprolites and your trace fossils what

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are you looking at to tell what was

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going on with life so back to our

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diagram and you can note that on this

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diagram the Hadean and the archaean the

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early anaerobic curator and read and

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tank and this is important because i'm

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going to show you this map and the

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archaean rocks and which also

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encompasses the hoodie and for these

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purposes also read in Peng so right away

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you can see when we go looking for rocks

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to find out about life from the early

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Earth we don't have a lot of rocks to go

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look at because not all of these are

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going to tell us about life life is

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primarily preserved in the sedimentary

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rock record not the igneous or the

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metamorphic because that's where life

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tends to live life isn't living and

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basalts and volcanoes it's living in the

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soil it's living in the sea floor so we

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have to find sedimentary rocks and they

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just started that many of them apart

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from the very top of North America most

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people also study Western Australia

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South Africa and the archaean rocks in

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India but not a lot was done with them

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so there's really only these two or

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three areas in the world where you can

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go to find these rocks and find out

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about the earlier so we have to work

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really hard with what we've got so what

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are we looking for in these rocks ins we

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don't have the bones and the coprolites

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and all that sort of thing and we're

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looking for evidence the life was there

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which can be microfossils although again

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we don't have a lot of microfossils for

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the early early Earth they start to

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emerge sort of two billion years ago

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really post grade oxidation event we're

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looking for evidence that life

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have been there we're looking for

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evidence that life could not have been

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there and if this is starting to sound

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like astrobiology you'd be right because

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this is the thing about early Earth

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geobiology for us the earliest is

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basically an alien planet it's this

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anaerobic world filled with prokaryotes

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where life as we know it doesn't really

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exist and the only way we can look at it

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is to study rocks and there's only a

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very few of these rocks because most of

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them have been destroyed so it's pretty

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much exactly like looking for life on

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Mars you're looking at the few rocks you

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can get hold of for a totally alien

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world so this is an alias geobiology

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isn't just important because it tells us

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thing about what alien wills might be

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like it is telling us about an alien

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world the beginning of their own so

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these are some of the kinds of things

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you look at when you're looking for

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evidence in the rocks microbial

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structures so not necessarily

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microfossils were you looking them under

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a microscope and seeing the actual

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microbes but structures created by

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microbes and some of you who are not

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geologists are probably looking at that

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and thinking the only structure I Syria

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there is a rock hammer and that's fair

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enough but this is a stromatolite this

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term stromatolite actually means a

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mattress rock because you have layers

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like mattresses and that create this

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structure I don't look a lot like

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matrices to me but clearly they look

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like mattresses to someone so that's

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what we're going with and if we zoom in

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close this is a pre-cambrian so not like

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super super early earth that like around

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the time of were just before the

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Cambrian extrusion stromatolite it's at

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Mount Dunphy and Nevada I was there a

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couple of months ago where I took this

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photo and you can see that there's all

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these fine fine layers and this

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fine-grained sandstone and we think

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these are being caused by little

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microbes growing and mounds and then the

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trapper trapping sediment some hair and

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it forms layers and these are then

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preserved in the rock record you also

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get going back to the gunflint should

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axle microfossils normally not for the

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very very early earth and there are some

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examples like that apex to it which we

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mentioned last night which are very

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hotly debated because they're kind of

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like um the Martian meteorite found in

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Antarctica they look like microbes but

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it's so long ago and the rocks so

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screwed up that are they microbes maybe

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maybe not but these are definitely

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so for the later early Earth we're

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really lucky we can actually see

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microbes in the rock but without these

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larger microbial structures and the

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microfossils what are we left with for

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these really old rocks that we don't

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have many of well there's a few proxies

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we can look at to think about life too

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and you'll hear about some of them today

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these isotopes which you're going to

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hear a lot more about from Bradley in

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just a few minutes and from speakers

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speakers later on this afternoon but

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essentially isotopes like carbon oxygen

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and sulfur can tell us things about the

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chemistry of the early Earth which can

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give us ideas about what sort of life

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could have been there and especially in

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terms of oxygen whether life was

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producing oxygen and what it was

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interacting with you have lipids and

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organic molecules things like DNA don't

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survive that long the oldest ancient DNA

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that we've managed to sequences maybe 30

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40 50 thousand years old these claims of

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all the stuff that it's pretty broken up

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but things like lipids can survive a

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really really long time again this isn't

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really relevant for the early early

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Earth and the best examples actually

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probably from the phanerozoic which is

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the modern earth i'll post the Cambrian

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explosion but you can get the

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preservation of lipids and the rock

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record and you can look at the lipids

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and think about the kind of things in

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the modern world that have those lipids

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and their name raves and so what it

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could mean about the life that could

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have been there and finally and kiefer

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geobiology there are minerals hooray so

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this is an example of a banded iron

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formation I'm sure a lot of you heard of

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these this is where in the great oaks

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around the time of the great oxidation

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event you had tons and tons of iron

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being laid down as the iron rusted with

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oxygen a man was laid down on these

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beautiful red layers and so these

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minerals are telling us again something

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about life on the early Earth because

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they're telling us about the oxygen and

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you get other minerals you get iron

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minerals that can be created by microbes

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by microbes that reduce an oxidized iron

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you get minerals and like sulfur sulfur

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minerals some of which you biogenic

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later on in the Earth's history you get

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carbonate minerals by organisms that are

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forming carbonate either directly by or

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by the influence on the environment so

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rocks are affected by life it's

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geobiology because the biology can

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create the geology

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not just coexisting with it and

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furthermore in early Earth geobiology we

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also have modern-day analogs so these

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places like deep-sea hydrothermal vents

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which are very hot there anaerobic and

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organisms are existing with the rock

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there's no sunlight and they're creating

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their own biosphere down there you have

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places like Yellowstone where you've got

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these hot springs and stromatolite just

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like the ones we see in the rock record

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are being created right now by organisms

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existing in the present day you have

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places like the Black Sea where you have

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a huge anoxic fascia basin and this

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really quite large sea and where the

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ocean is anaerobic like we think it was

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in the early Earth now it's not a

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perfect analogue because our the

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concentrations of a lot of things like

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sulfur very different but it's still a

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hole in aerobic section of ocean that we

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can go look at to see how organisms are

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getting on because there ain't no fish

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down there it's just microbes just like

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we think it was on the early Earth but

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really the point of all this forces

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astrobiologists is that if we know what

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life looks like in the rock record here

348
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and the signs it leaves behind we can

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understand what it might leave behind on

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other planets and how we can really

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adequately go out to Mars and say and

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look at the rocks and say this is

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geobiology these are the signs of what

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life left behind there just like it did

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so I'm going to be rude and take the

356
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first question myself I was intrigued by

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the rock distribution map that you put

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up at the beginning yep what is it about

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northern North America that is the sole

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source or primary source of that

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sedimentary stuff is it glaciers so it's

362
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not the primary source Western Australia

363
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and South Africa a little better that

364
00:13:00,290 --> 00:12:58,680
was the best picture I i had but the

365
00:13:02,270 --> 00:13:00,300
thing about North America as you have

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the sort of crate on which is the center

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of north america and it's like a

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continental the center of a continent

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that's head staff added on to it and

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stuff broken off of the edges but the

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center is really old and that's why you

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have all these old old rocks preserved

373
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any other questions yep so you showed

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00:13:36,350 --> 00:13:34,170
this picture of a layered rock and you

375
00:13:38,300 --> 00:13:36,360
said that you think his layers are

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formed by bacteria I can't explain how

377
00:13:42,170 --> 00:13:40,620
you know that these layers are formed by

378
00:13:44,300 --> 00:13:42,180
bacteria so that's a great question

379
00:13:45,860 --> 00:13:44,310
because I'm the original thinking was

380
00:13:47,780 --> 00:13:45,870
that wall stromatolites were formed by

381
00:13:49,280 --> 00:13:47,790
bacteria and there's a growing idea that

382
00:13:51,980 --> 00:13:49,290
actually a lot of stromatolite X

383
00:13:54,020 --> 00:13:51,990
structures aren't necessarily microbial

384
00:13:56,030 --> 00:13:54,030
how you can usually tell as you have

385
00:13:58,280 --> 00:13:56,040
layers and they'll lay down flat to be

386
00:14:00,440 --> 00:13:58,290
laid up but the flat is along a cone

387
00:14:03,320 --> 00:14:00,450
shape and the grains are trapped in ways

388
00:14:04,790 --> 00:14:03,330
where if it was just dropping on there

389
00:14:06,590 --> 00:14:04,800
they would have rolled off if they were

390
00:14:07,880 --> 00:14:06,600
being trapped by something sticky and we

391
00:14:10,040 --> 00:14:07,890
think the most likely thing in those

392
00:14:11,450 --> 00:14:10,050
situations as there were organisms they

393
00:14:13,550 --> 00:14:11,460
were producing sticky extra

394
00:14:14,960 --> 00:14:13,560
polysaccharides or they actually fill

395
00:14:17,030 --> 00:14:14,970
them into scrolling around the grains

396
00:14:18,830 --> 00:14:17,040
and that's why they're being trapped you

397
00:14:20,420 --> 00:14:18,840
can certainly have structures that look

398
00:14:22,580 --> 00:14:20,430
like that but if you look at the

399
00:14:24,440 --> 00:14:22,590
microstructure it's hard to think of

400
00:14:26,060 --> 00:14:24,450
ways that biology could have been

401
00:14:28,400 --> 00:14:26,070
involved so there's definitely a range

402
00:14:33,230 --> 00:14:28,410
not all stromatolite say you know as are

403
00:14:34,550 --> 00:14:33,240
definitely biological but a lot are all

404
00:14:36,540 --> 00:14:34,560
right we need to move on so let's thank