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This is geology B with Oliver 
stimple. 

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We don't know very much about 
the first six, hundred million 

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years of Earth history, which we
call the hidden Eon nor indeed 

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do we know that much about the 
beginning of the archean, Eon 

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that followed but that is 
beginning to change as 

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researchers deploy the modern 
tools of geochronology and 

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geochemistry. 
There are two main questions 

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being investigated, the first 
concerns, the crust when and by 

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What mechanisms did it become 
something like the crust we have

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today with, its thick. 
Tenants and thin subducting 

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seafloor. the second question, 
which is closely related to the 

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first concerns life when did the
Earth first become habitable, In

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an earlier episode, Peter cawood
talked about the first question.

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And in particular, about when 
modern style plate, tectonics 

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may have started. 
And in another episode John 

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Valley, discussed the early 
Earth, suggesting that the Earth

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might have cooled more rapidly 
than was previously thought and 

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thus become habitable very early
in its history. 

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Nacho bonds research is also 
directed to the study of the 

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early Earth by analyzing a 
newly. 

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Discovered Trove of extremely 
ancient Zircon crystals. 

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She has given us a new lens into
the hadean and early archaea 

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Neons. 
This has enabled us to witness 

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some of the processes that 
created and destroyed the hadean

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and early, archean crust. 
We can then use this knowledge 

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to make inferences about when 
the earth first became 

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habitable. 
Nadia turbine is assistant 

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professor of Earth, and 
planetary Sciences at Harvard 

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University. 
Not yet Robin. 

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Welcome to Joel g, b. 
Thank you so much for having me.

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Before we talk about the newly 
discovered zircons, can you 

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remind us as to why zircons are 
so useful as probes of the early

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Earth? 
Yeah, so dragons are an 

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incredibly powerful tool for, 
for different reasons. 

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So firstly zarkon is really 
abundant and felsic crust. 

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Secondly, it's very durable. 
It's very resistant to 

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alteration weathering. 
Then, thirdly, of course, we can

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date it and I believe your 
listeners have heard plenty 

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about Zircon, uranium that 
geochronology already and then, 

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lastly, this tiny zarkon's 
actually capture a lot of 

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geochemical information, so that
includes isotopic records as 

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well as trace and worth laments 
that tell us about crustal 

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conditions experienced during 
zarkan crystallization. 

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Okay, good. 
We'll get into that in a moment,

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but just to clarify, its the 
Zircon crystals themselves. 

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That are indestructible and 
we're dealing with detrital 

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zircons here. 
So these has a concert got 

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eroded out of the igneous rocks 
in which they originally formed,

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and then later on got 
incorporated into sedimentary 

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rocks in an earlier podcast off 
liniment talked about using 

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detrital zircons to trace the 
Assembly of Europe. 

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In the Paleozoic here, we're 
dealing with much older detrital

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zircons to probe processes that 
happened in the hadean, an early

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archean. 
How old are the Oldest Zircon 

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crystals and how old are the 
oldest intact rocks? 

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This is really a problem we face
when we study early Earth 

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history, right? 
Because as we go further back in

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time we lose the rock record so 
the archean Eon represents 1.5 

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billion years of Earth's 
history. 

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So really significant chunk of 
resistor e but only 5% of rocks 

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of that age. 
So the oldest rock is 4 point 0 

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3, billion years old, the 
struggles from the accursed 

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ignites, complex and Canada. 
The sleeves. 

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The first over 500 million years
of Earth's history without a 

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rock record. 
We find a few locations around 

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the globe where the hadean 
zarkon's but the oldest circle 

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on that we have found is about 
4.4 billion years old. 

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Okay. 
So that's not much but still 

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older than the actual oldest 
rock itself. 

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Yeah. 
That's about 400 million years 

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older. 
So can you tell us about the 

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ancient zircons that were known 
before this new source that I 

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just mentioned was discovered? 
Yeah so the Most famous location

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with Heidi, and Zircon is that 
jackets and Western Australia. 

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So the first hadean zarkon's 
there were discovered in the 80s

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and since then people have dated
about 200,000 zarkon's. 

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So that's really a huge amount 
of work and of these 200,000 

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zarkon's about 10,000 where 
hadean and Age and what is 

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really so great about this 
location is that it allowed us 

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to first start addressing some 
of these big questions that we 

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have about the early Earth. 
So those questions When did the 

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first crust form the early Earth
was initially covered by magma 

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ocean. 
So when did we start forming 

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crust? 
And when did we start forming 

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oceans on this crust. 
What was the composition of that

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question? 
Does it tell us anything about 

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Geo Dynamics? 
So one big question that I'm 

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trying to address and my 
research is the evolution of 

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tectonic processes. 
So Earth is the only planet in 

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the solar system that has paid 
tectonics. 

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We don't really know when plate 
tectonics started and why it 

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started And then the last big 
question of course is when did 

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life evolve and that question is
really two components when did 

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Earth first become habitable. 
And then, when do we actually 

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start finding physical evidence 
for life? 

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The problem that the jackals is 
that it's only a single 

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location. 
So that, of course, it's not 

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very representative holder whole
earth. 

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So, tell us about the newly 
discovered zircons. 

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You found in the Barberton 
greenstone belt in South Africa.

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We found a new location that. 
Hey, Ends are caught in South 

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Africa and the Barberton 
greenstone belt. 

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So the Barberton rinse them 
Boulders between about 3.6 the 

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3.2 billion years old. 
And within this greenstone belt 

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we have data about 100 different
sand Stones throughout the unit 

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and we found one single 
Sandstone that contained hadean 

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zarkon's and the Sandstone is 
called the green cents on bad 

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because it's very green. 
So it contains a lot of chromium

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Rich faces, which gives it that 
green color and What is so 

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fascinating about this unit? 
Is that the zircons? 

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We find in them have ages, that 
do not correspond to any known. 

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Felsic igneous rock within the 
Barberton group. 

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So it really yields information 
about a Terrain that has since 

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been lost and this terrain has 
an age between 4.15 to about 3.3

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1 billion years. 
So that's 800 million years of 

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history that we can tap by 
studying the ages and the 

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geochemistry of these zircons 
being able to look at this. 

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Complimentary record to the Jack
hilts allows us to start testing

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some of the hypotheses. 
They were put forward based on 

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the results from the Jack Hills 
and what is nice about the green

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Sandstone bed is that The Rock 
experience lower temperatures 

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compared to the jackals so it's 
somewhat better preserved. 

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Unfortunately what is not as 
good as the jackals that in the 

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Jack Hills between 3 and 12 
percent of the zircons. 

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I hate Ian and age versus in the
green sense in bed. 

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It's only half a percent of the 
zircons, okay? 

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So let's talk about the Way, you
analyzed these zircons from 

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South Africa in the previous 
episode, with geology, B, I 

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talked to John Cottle about a 
technique for rapid and 

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self-consistent dating and 
measuring of Trace, element, 

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abundances and crystals such as 
zircons. 

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Did you use his methods? 
We did not use his methods. 

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So John Cotton use laser 
ablation, split stream analysis,

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which allows you to measure the 
ages and the hafnium isotope 

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composition. 
Perhaps also Trace elements of 

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exactly the Amount of material. 
And we did not do that in part. 

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Because we needed much more 
precise results as I mentioned, 

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only a half, a percent of the 
Zircon are hadean and age. 

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So first, we analyze as many 
zircons as we can at a 

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relatively rapid speed, to just 
be able to find the oldest 

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grains. 
And then we take the mounts with

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the zircons on them and we put 
them into a shrimp. 

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Let me interject that this 
shrimp is not a crustacean, but 

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an acronym for an Instrument 
called a sensitive high 

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resolution iron microprobe. 
Yeah, shrimp allows much more, 

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precise dating. 
So we dated the old grains. 

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And then we also use shrimp to 
do Trace, elements analysis, and

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this is really important to use 
shrimp for that. 

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A because some elements that we 
are studying have incredibly 

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low, abundance of, but also 
because some of the elements 

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that are particularly important 
have interferences. 

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So, you need really high 
resolution to really analyze the

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Correct Peaks. 
So you performed then, several 

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geochemical analyses on the 
zircons, can you tell us about 

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those? 
I use three different analytical

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approaches. 
The first one is we measured 

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hafnium Isotopes to get at crust
mantle differentiation, then we 

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measure trace and Rare Earth 
elements, which tells us about 

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the composition at the magma at 
Zircon crystallization. 

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And then, lastly, we used oxygen
Isotopes, which can tell us 

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about the It's of a hydrosphere 
in the hadean. 

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Let's go through these one at a 
time. 

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Let's start with the hafnium 
analysis. 

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How does that work? 
What can the results of that 

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analysis? 
Tell us when we study hafnium 

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Isotopes and Zircon. 
What we really focus on is the 

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decay of 176 lutetium, 2176 
hafnium. 

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So lutetium and hafnium have 
very different behavior lutetium

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is relatively compatible. 
So it's going to preferentially 

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stay. 
The mantle versus hafnium is 

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much more compatible. 
So it's going to prefer actually

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go into the crust. 
What we ultimately end up 

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measuring, is the 176 hafnium. 
So the daughter product of that 

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decay over the stable, 177 
hafnium, which is relatively 

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constant through Earth history. 
So because of this different 

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behavior. 
When we look at these different 

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reservoirs, they show a 
different change in the daughter

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products, 176 hafnium over 177 
happening. 

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Ooh time because the mental 
contains more lutetium. 

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The increase in the 176 hafnium 
over. 177 hafnium is going to be

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much more than, for example, 
continental crust, because 

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continental crust has less 
lutetium. 

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That means, it produces less 176
hafnium. 

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And that means that the increase
in the ratio of 176 hafnium 

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over. 177 hafnium is going to be
smaller Zircon is a really 

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fantastic tool to track. 
What they have neum isotopic. 

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Composition was of the magma at 
the time, the Zircon 

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crystallized because when Zircon
crystallizes it takes up to 

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several rate percent of hafnium,
but almost no lutetium, so it 

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essentially freezes the signal, 
the isotopic signal of the 

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hafnium Isotopes at the time it 
crystallises. 

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So depending on the ratio of the
176 hafnium over 177 happening, 

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we can now say What's that crust
extracted from the mantle like 

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immediately prior to Zircon 
crystallization? 

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Essentially, or did the circle 
actually formed by remelting of 

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old crust? 
So, as I mentioned, again, 

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order, continental crust has a 
different change in the ratio of

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176 hafnium over 177 hafnium. 
So it really deviates a lot from

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the evolution of the mantle. 
So, if we take this old crust 

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and remelt it, the Zircon can 
again capture the signal, and we

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can use that too. 
Confer those are conformed from 

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this order crust or from more 
juvenile. 

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So like newly-formed crust from 
the metal. 

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Wow, that's really impressive. 
We can actually use the hafnium 

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isotope ratios and zarkon's to 
tell whether hadean and eliachim

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crustal rocks, which themselves 
have long since disappeared, 

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were made directly by melting of
the mantle or by melting of 

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pre-existing older crust. 
So, can you tell us about the 

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results of your hafnium isotope 
analysis? 

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Yes, And the green, send some 
bad. 

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When we look at the oldest 
zarkon's, we can see that there 

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are extracted from the mantle. 
About four point two to four 

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point four billion years ago. 
And for the next four to six 

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hundred million years. 
There's a constant not record 

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any evidence of new mental 
additions. 

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Instead it seems like that that 
initial cross that was extracted

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from the mental stayed. 
Relatively isolated, there was 

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some internal remoting but there
were no new edition. 

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Of mantle material and then that
signal abruptly changes about 

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3.8 billion years ago, anything 
younger than 3.8. 

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We see a lot of new additions 
from their Mentor. 

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So a lot of juvenile, felsic 
crust production together with 

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some remelting of older crust 
but that isotopic signal of 

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they're really old. 
Hadean crust is essentially lost

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after about 3.8 billion years 
ago now, that's fascinating. 

226
00:13:01,700 --> 00:13:07,200
So points to a change that 
happened about 3.8 billion 

227
00:13:07,200 --> 00:13:10,900
years, you're already getting 
into the early archean. 

228
00:13:11,000 --> 00:13:14,500
Let's talk about the other 
analyses first before we Circle 

229
00:13:14,500 --> 00:13:17,300
back and then talk about what 
you manage to conclude from 

230
00:13:17,300 --> 00:13:21,100
putting all this together. 
So, the second analysis you 

231
00:13:21,100 --> 00:13:23,400
mentioned earlier. 
It was about looking at the 

232
00:13:23,400 --> 00:13:26,200
trace and Rare Earth element 
abundances that you measured in 

233
00:13:26,200 --> 00:13:28,000
the zarkon's. 
Yeah, that's right. 

234
00:13:28,000 --> 00:13:32,700
So trace and Rare Earth elements
have been used for decades at 

235
00:13:32,700 --> 00:13:35,400
this point, but it's only really
been the last 10 years. 

236
00:13:35,500 --> 00:13:39,000
Is that researchers have 
recognized that they really 

237
00:13:39,000 --> 00:13:42,200
provide a lot of information in 
terms of that setting in which 

238
00:13:42,200 --> 00:13:46,000
the zircons crystallized. 
So for this query Grimes 

239
00:13:46,000 --> 00:13:50,100
analysts are cons from felsic 
igneous, rocks in different 

240
00:13:50,100 --> 00:13:53,700
tectonic, magnetic settings so 
that includes depleted. 

241
00:13:53,700 --> 00:13:56,800
Mantle, so mid-oceanic ridges 
under pleaded mental. 

242
00:13:56,800 --> 00:13:59,700
So that's something that would 
be represented by ocean islands.

243
00:13:59,700 --> 00:14:03,600
Like, Hawaii or Iceland. 
And then, lastly, he looked at 

244
00:14:03,600 --> 00:14:06,600
Continental arcs. 
So, Subduction zones, right? 

245
00:14:06,600 --> 00:14:08,100
That's a very different 
mechanism. 

246
00:14:08,100 --> 00:14:11,700
You're pushing crust below a 
continent and that setting. 

247
00:14:11,900 --> 00:14:14,600
And you've got this type of 
hydro smelting signature. 

248
00:14:15,400 --> 00:14:19,300
So he quite Grimes ultimately 
found that there's some very 

249
00:14:19,300 --> 00:14:23,000
specific Trace elements that can
really distinguish these 

250
00:14:23,000 --> 00:14:26,600
different tectonic magmatic 
processes and these include 

251
00:14:26,600 --> 00:14:30,400
uranium niobium Scandium serum 
and ytterbium. 

252
00:14:30,900 --> 00:14:34,400
So what do our zarkon's show 
right that's the big question 

253
00:14:34,400 --> 00:14:38,900
here and For this long-lived 
crust that was extracted from 

254
00:14:38,900 --> 00:14:41,300
the mantle in the hadean that I 
mentioned earlier. 

255
00:14:41,300 --> 00:14:44,400
The question is really okayed, 
this Quest has really long lived

256
00:14:44,400 --> 00:14:47,900
but how did it form initially? 
Did it form in a type of Arc 

257
00:14:47,900 --> 00:14:50,200
setting, which would be evidence
of plate tectonics? 

258
00:14:50,500 --> 00:14:53,600
Or did it form in a more mental 
dominated, setting. 

259
00:14:53,900 --> 00:14:56,000
That is something. 
We cannot distinguish by using 

260
00:14:56,000 --> 00:14:59,100
hafnium Isotopes. 
But now, by using the trace 

261
00:14:59,100 --> 00:15:02,100
elements, we actually find that 
these earliest zircons have a 

262
00:15:02,100 --> 00:15:05,300
really strong mental signature 
and very little evidence for 

263
00:15:05,500 --> 00:15:08,200
Just melting that we would 
expect for example, in a 

264
00:15:08,208 --> 00:15:12,400
subduction setting because you'd
expect the hydras in volcanic 

265
00:15:12,400 --> 00:15:15,700
rock in a subduction zone 
because that would normally be 

266
00:15:15,700 --> 00:15:17,800
happening under the ocean. 
Yeah. 

267
00:15:17,800 --> 00:15:21,400
Because you have got the oceanic
crust that is interacting with 

268
00:15:21,400 --> 00:15:24,000
the ocean. 
And then that crossed that is 

269
00:15:24,000 --> 00:15:28,100
hydrated is being pushed 
underneath another crust and 

270
00:15:28,100 --> 00:15:31,500
that water is being used in the 
melting process and other parts 

271
00:15:31,500 --> 00:15:33,900
are very characteristic your 
chemical signature. 

272
00:15:34,300 --> 00:15:36,600
So, by looking at the Green 
Sandstone bad. 

273
00:15:36,600 --> 00:15:39,400
I mentioned earlier, the hafnium
Isotopes that we have evidence 

274
00:15:39,400 --> 00:15:42,300
that there was an initial cost 
extraction and that that crust 

275
00:15:42,300 --> 00:15:45,300
has really long lived by using 
the trace elements. 

276
00:15:45,300 --> 00:15:49,100
We are able to say that that 
initial crust was extracted from

277
00:15:49,100 --> 00:15:52,500
the mantle and so it doesn't 
have that strong Hydro smelting 

278
00:15:52,500 --> 00:15:56,300
signature. 
So this is really remarkable. 

279
00:15:56,500 --> 00:16:00,400
Because this Oceanic type crust 
was stable for several hundreds 

280
00:16:00,400 --> 00:16:03,900
of millions of years, which is 
something that is really not 

281
00:16:03,900 --> 00:16:05,900
typical. 
When you look at the Water and 

282
00:16:05,900 --> 00:16:08,300
environment today. 
So when you think for example, 

283
00:16:08,300 --> 00:16:11,600
about oceanic crust, oceanic 
crust typically doesn't get 

284
00:16:11,600 --> 00:16:14,700
older than 200 million years 
verse 8, he didn't cross that 

285
00:16:14,700 --> 00:16:17,300
formed the source to the green 
sense and that was stable for 

286
00:16:17,300 --> 00:16:20,500
hundreds of millions of years. 
So this is already starting to 

287
00:16:20,500 --> 00:16:23,600
give us some indication that 
some of the early Earth. 

288
00:16:23,600 --> 00:16:26,700
Geodynamic processes may have 
been rather different to today. 

289
00:16:27,300 --> 00:16:30,400
So you also analyze oxygen 
Isotopes. 

290
00:16:30,900 --> 00:16:33,500
What does that? 
Tell us, oxygen Isotopes and 

291
00:16:33,500 --> 00:16:35,300
Zircon. 
Tell us something different. 

292
00:16:35,400 --> 00:16:38,300
Aunt oxygen Isotopes and Zircon 
is I really sensitive Tracer of 

293
00:16:38,300 --> 00:16:42,600
fluid solid interactions. 
So tells us if the magma from 

294
00:16:42,600 --> 00:16:46,600
which the Zircon crystallised 
has assimilated across, that was

295
00:16:46,700 --> 00:16:49,400
out at low temperature or 
potentially something that 

296
00:16:49,400 --> 00:16:52,700
incorporated sediments. 
So that implies there was some 

297
00:16:52,700 --> 00:16:55,800
kind of hydrosphere already at 
the surface of the Earth. 

298
00:16:56,000 --> 00:16:59,500
It can also tell us if that 
interaction with a potential 

299
00:16:59,500 --> 00:17:02,900
hydrosphere happened at high 
temperatures, is it possible to 

300
00:17:02,900 --> 00:17:07,400
explain in simple terms, why? 
With the hydrosphere would 

301
00:17:07,500 --> 00:17:10,200
affect the oxygen, isotope 
ratios. 

302
00:17:10,300 --> 00:17:13,700
So, this is something that is 
based on an isotope equilibrium 

303
00:17:13,700 --> 00:17:16,400
process. 
That really depends on the mass 

304
00:17:16,400 --> 00:17:18,900
of the oxygen. 
And you have different exchange 

305
00:17:18,900 --> 00:17:21,800
between the material that you 
are altering and the fluid and 

306
00:17:21,800 --> 00:17:24,200
that's going to vary depending 
on the temperature. 

307
00:17:24,400 --> 00:17:26,500
But this is an entirely in 
organic process. 

308
00:17:26,500 --> 00:17:29,800
Correct. 
So, we already know from the 

309
00:17:29,800 --> 00:17:32,500
jackals that most of those are 
concept of mental, like, 

310
00:17:32,500 --> 00:17:35,200
signature in a few of them to 
show evidence. 

311
00:17:35,600 --> 00:17:38,200
For alterations with low 
temperature fluid. 

312
00:17:38,200 --> 00:17:41,500
So that there's some evidence 
for hydrosphere, but here the 

313
00:17:41,500 --> 00:17:44,800
question of course, always is. 
Okay, it's only one location. 

314
00:17:45,000 --> 00:17:47,200
So was the global Ocean or was 
it? 

315
00:17:47,200 --> 00:17:50,400
Maybe just something more 
localized in South Africa. 

316
00:17:50,500 --> 00:17:54,800
What we find is also a lot of 
Sir concert at elevated oxygen 

317
00:17:54,800 --> 00:17:58,200
isotope signature. 
So this is providing us with a 

318
00:17:58,208 --> 00:18:00,400
better picture of a potentially 
more. 

319
00:18:00,400 --> 00:18:02,900
Widespread hydrosphere already 
in the hadean. 

320
00:18:03,800 --> 00:18:07,400
Okay. 
So can you put the results of 

321
00:18:07,400 --> 00:18:10,900
these three sets of analyses 
together? 

322
00:18:11,300 --> 00:18:14,600
The hafnium Isotopes. 
The trace and Rare Earth 

323
00:18:14,600 --> 00:18:18,200
elements, and the oxygen 
Isotopes and tell us what you 

324
00:18:18,200 --> 00:18:21,800
were able to learn about the 
crust of the early Earth from 

325
00:18:21,900 --> 00:18:24,100
the South African zircons. 
Yeah. 

326
00:18:24,100 --> 00:18:26,800
Sure. 
So in South Africa, we learned 

327
00:18:27,000 --> 00:18:29,500
that there's really two phases 
in the crust. 

328
00:18:29,500 --> 00:18:33,100
Evolution prior to 3.8, billion 
years ago. 

329
00:18:33,300 --> 00:18:38,200
We Crust formation by extraction
of material from the mantle and 

330
00:18:38,200 --> 00:18:40,100
this material from the mentors 
extract. 

331
00:18:40,100 --> 00:18:42,300
It and was kept relatively 
isolated. 

332
00:18:42,300 --> 00:18:44,500
So we don't see a lot of 
juvenile editions, it's 

333
00:18:44,500 --> 00:18:48,100
relatively stable, but we do 
find evidence that there was 

334
00:18:48,100 --> 00:18:52,000
some present water and then 
after 3.8, we see this really 

335
00:18:52,000 --> 00:18:56,200
dramatic change, very knows that
seeing a lot of new juvenile 

336
00:18:56,200 --> 00:18:58,300
editions. 
The crust becomes really 

337
00:18:58,300 --> 00:19:00,800
unstable. 
You're still mixing some older 

338
00:19:00,800 --> 00:19:04,900
material, but we do start seeing
this really Mork Hydra smelting 

339
00:19:04,900 --> 00:19:10,500
signatures so is this a period 
of history that we did not have 

340
00:19:10,500 --> 00:19:12,400
access to before? 
Then when we were just looking 

341
00:19:12,400 --> 00:19:16,300
at the Jack Hills, it is really 
providing a complimentary 

342
00:19:16,300 --> 00:19:18,600
record. 
So tying the have new Isotopes 

343
00:19:18,600 --> 00:19:21,400
and the trace elements. 
It's starting to add a lot of 

344
00:19:21,400 --> 00:19:24,700
different puzzle pieces to this 
picture of the hadean that we 

345
00:19:24,700 --> 00:19:27,800
are trying to put together. 
What was the earliest earth like

346
00:19:27,800 --> 00:19:31,800
was a very similar to today. 
I was different and there's this

347
00:19:31,800 --> 00:19:33,900
really wonderful study by any 
Our. 

348
00:19:33,900 --> 00:19:36,500
And she looked at hafnium 
Isotopes from a number of 

349
00:19:36,500 --> 00:19:40,200
different locations around the 
globe and she found that this 

350
00:19:40,300 --> 00:19:43,000
Evolution and the hafnium 
Isotopes showing really 

351
00:19:43,000 --> 00:19:47,200
long-lived crust during the 
early Earth until about 3.8 3.6 

352
00:19:47,200 --> 00:19:50,400
billion years ago. 
And then suddenly we see this 

353
00:19:50,400 --> 00:19:53,800
destabilization and more 
juvenile Quest, editions, but 

354
00:19:53,800 --> 00:19:56,900
again having him Isotopes, can't
really tell us if that 

355
00:19:56,900 --> 00:19:59,900
long-lived crust was formed by 
some kind of plate, tectonic 

356
00:19:59,900 --> 00:20:04,900
process, or something different.
So now Tying the trace elements.

357
00:20:04,900 --> 00:20:07,700
We can say that at least for the
green Sandstone bad. 

358
00:20:07,700 --> 00:20:10,000
We see this transition of 
something that is more mental, 

359
00:20:10,000 --> 00:20:13,500
dominated until about 3.8. 
And then the signatures start 

360
00:20:13,500 --> 00:20:16,700
becoming a little more similar, 
does that suggest that plate 

361
00:20:16,700 --> 00:20:18,700
tectonics might have started at 
that time? 

362
00:20:18,800 --> 00:20:21,600
Or are there other explanations 
for what we've seen in the 

363
00:20:21,600 --> 00:20:23,700
record? 
That's a really good question 

364
00:20:23,700 --> 00:20:26,400
because that's something we have
to be really careful about. 

365
00:20:26,700 --> 00:20:29,800
So starting at three point eight
and the trace elements, we start

366
00:20:29,800 --> 00:20:33,400
seeing a hydro smarting 
signature and the thing is that 

367
00:20:33,600 --> 00:20:37,400
Different processes that could 
explain the type of signature 

368
00:20:37,900 --> 00:20:40,600
one way is the standard way that
we see today, right? 

369
00:20:40,600 --> 00:20:43,100
Plate tectonics. 
That's the tectonic model that 

370
00:20:43,100 --> 00:20:46,700
we are used to, where we talked 
about this earlier already where

371
00:20:46,700 --> 00:20:51,400
we're putting hydrated, oceanic 
crust into the mantle and I turn

372
00:20:51,400 --> 00:20:53,400
it of way. 
How this might have happened 

373
00:20:53,400 --> 00:20:57,500
during the early Earth? 
Is that when you form a crust at

374
00:20:57,500 --> 00:21:00,500
the surface and why it's at the 
surface, it's interacting with 

375
00:21:00,500 --> 00:21:03,300
the hydrosphere potentially, you
are generating sub. 

376
00:21:03,500 --> 00:21:07,000
Is that are being deposited, if 
that costs us buried. 

377
00:21:07,000 --> 00:21:11,000
So, imagine just a lot of really
heavy mantle material coming up 

378
00:21:11,000 --> 00:21:13,700
to the surface. 
So the crust thickens and it 

379
00:21:13,700 --> 00:21:16,800
starts sinking down. 
So we call that sect action or 

380
00:21:16,800 --> 00:21:19,800
partial convective. 
Overturn, you might be able to 

381
00:21:19,800 --> 00:21:23,100
generate a similar signature and
that Trace elements. 

382
00:21:23,100 --> 00:21:26,200
And I have new, my sister topes 
sack duction as opposed to 

383
00:21:26,200 --> 00:21:29,900
subduction sag so just like a 
sag a block just falls off. 

384
00:21:30,100 --> 00:21:32,300
Yeah it just pods are so 
psyched. 

385
00:21:32,300 --> 00:21:37,200
Action was She possible and the 
achaean because the heat flux on

386
00:21:37,200 --> 00:21:40,400
The Mantel was higher. 
So the crossbows generally 

387
00:21:40,400 --> 00:21:43,300
hotter and because of that, the 
crust started behaving in 

388
00:21:43,300 --> 00:21:47,400
different ways potentially 
allowing for that sagging versus

389
00:21:47,500 --> 00:21:50,400
today, the heat flux on the 
mental is much lower, which 

390
00:21:50,400 --> 00:21:53,700
makes the crust, much more 
rigid, and does not allow for 

391
00:21:53,700 --> 00:21:57,400
that sagging Behavior. 
Sagged action has been proposed 

392
00:21:57,400 --> 00:22:00,000
for ancient rocks, but we don't 
see you today. 

393
00:22:00,300 --> 00:22:02,200
What exactly does the signature 
look like? 

394
00:22:02,300 --> 00:22:05,300
I hope that one day. 
Some Modelers will go and model 

395
00:22:05,300 --> 00:22:08,400
that and can tell us if there's 
ways to distinguish the two 

396
00:22:08,400 --> 00:22:10,500
different. 
Signatures I said in my 

397
00:22:10,500 --> 00:22:13,700
introduction that you can use 
the knowledge, your honor thing 

398
00:22:13,700 --> 00:22:17,300
about the early crust to make 
inferences as to when the earth 

399
00:22:17,300 --> 00:22:20,100
first became habitable. 
What does all this have to do 

400
00:22:20,100 --> 00:22:23,600
with habitability? 
I think that there are three 

401
00:22:23,600 --> 00:22:27,300
important takeaways and regards 
to habitability. 

402
00:22:27,300 --> 00:22:31,500
So the first one relates to the 
presence of water, we all need 

403
00:22:31,500 --> 00:22:34,900
water. 
So The question is, when did we 

404
00:22:34,900 --> 00:22:37,500
start forming a hydrosphere? 
When did we start farming? 

405
00:22:37,500 --> 00:22:41,300
And ocean and based on previous 
results and the jackals and our 

406
00:22:41,300 --> 00:22:45,100
new results now and South 
Africa, we can say that at least

407
00:22:45,100 --> 00:22:48,100
by about 4.3 4.2 billion years 
ago. 

408
00:22:48,300 --> 00:22:50,800
That was probably a hydrosphere 
present. 

409
00:22:51,100 --> 00:22:55,700
The second one is about the 
creation of typography. 

410
00:22:56,000 --> 00:23:00,100
So today, the most effective 
mechanism of creating Topography

411
00:23:00,100 --> 00:23:03,400
is through plate, tectonics and 
convergent settings. 

412
00:23:03,600 --> 00:23:07,500
So, this is becomes really 
important when you think about 

413
00:23:07,500 --> 00:23:11,300
what the conditions at the 
surface were today, with 

414
00:23:11,300 --> 00:23:14,800
creating topography reinitiate 
silicate, weathering, and that 

415
00:23:14,800 --> 00:23:19,800
draws CO2 out of the atmosphere,
it fixes it into carbonate, that

416
00:23:19,800 --> 00:23:22,100
makes the climate much more 
moderate. 

417
00:23:22,400 --> 00:23:26,000
So if we don't have plate 
tectonics, be a volcano, still 

418
00:23:26,000 --> 00:23:29,400
producing CO2 going into the 
atmosphere, making it really 

419
00:23:29,400 --> 00:23:32,700
hard but you don't have a good 
way to draw that. 

420
00:23:32,700 --> 00:23:35,700
CO2 down. 
So one question is okay. 

421
00:23:35,700 --> 00:23:38,400
When did we start creating all 
of that topography? 

422
00:23:38,400 --> 00:23:42,500
And it looks like in terms of 
mechanisms, it seems like 

423
00:23:42,500 --> 00:23:45,200
starting a 3.8 that might have 
been much more efficient 

424
00:23:45,200 --> 00:23:47,300
mechanisms of creating that 
typography. 

425
00:23:47,500 --> 00:23:49,800
So, just really stabilizing the 
climate. 

426
00:23:50,500 --> 00:23:54,900
If the climate was really 
changing and fluctuating up and 

427
00:23:54,908 --> 00:23:57,500
down, you can still have life, 
but the conditions are going to 

428
00:23:57,508 --> 00:23:59,900
be more favorable for more 
substantial biomass. 

429
00:23:59,900 --> 00:24:04,200
Once you start stabilizing the 
climate and then the last 

430
00:24:04,200 --> 00:24:09,100
evidence is more direct path and
Bal in the Jack Hills, studied 

431
00:24:09,100 --> 00:24:12,800
the mineral, inclusions of 
zircons and she found at least 

432
00:24:12,800 --> 00:24:15,700
one zarkon that has to graphite 
inclusions. 

433
00:24:15,900 --> 00:24:20,300
So graphite as carbon and carbon
could potentially be evidence 

434
00:24:20,300 --> 00:24:24,300
for life and she measured the 
carbon isotope composition. 

435
00:24:24,700 --> 00:24:27,700
So carbon has heavier and 
lighter isotope. 

436
00:24:27,700 --> 00:24:32,100
So carbon 13 and carbon 12 and 
live, always prefers, the light 

437
00:24:32,100 --> 00:24:36,200
isotope if the Carbon Isotopes 
are relatively - this could 

438
00:24:36,200 --> 00:24:38,000
potentially be evidence for 
life. 

439
00:24:38,400 --> 00:24:41,100
And this graphite inclusions 
that she measured, she found 

440
00:24:41,100 --> 00:24:44,300
carbon isotope value of minus 
24, which is very much 

441
00:24:44,300 --> 00:24:47,500
consistent with life already 
being present during the early 

442
00:24:47,500 --> 00:24:51,100
Earth and I'm saying consistent 
because it just one inclusion. 

443
00:24:51,100 --> 00:24:54,800
So we need to be really careful.
There are some abiotic mechanism

444
00:24:54,800 --> 00:24:57,700
that could produce carbon 
Isotopes like that but this is 

445
00:24:57,700 --> 00:25:00,500
something that I'm hoping to do 
in future researchers. 

446
00:25:00,600 --> 00:25:02,800
Search for more graphite 
inclusions and measure the 

447
00:25:02,800 --> 00:25:06,900
carbon The topes to see if we 
continuously get these light 

448
00:25:06,900 --> 00:25:09,600
carbon isotopes. 
That could be reflective of 

449
00:25:09,600 --> 00:25:13,400
early life or if we find more 
graphite, inclusions do receive 

450
00:25:13,400 --> 00:25:17,100
range and carbon Isotopes which 
would speak to more abiogenic 

451
00:25:17,100 --> 00:25:19,300
mechanisms. 
You mentioned how useful it 

452
00:25:19,300 --> 00:25:21,600
would be to look for other 
locations. 

453
00:25:21,900 --> 00:25:25,400
Are you actually hunting for new
sources of ancient zircons? 

454
00:25:25,800 --> 00:25:29,500
I think that absolutely are more
locations with hadean zircons 

455
00:25:29,600 --> 00:25:33,900
and on a lot of my research 
projects, we just analyze a On 

456
00:25:33,900 --> 00:25:36,600
spotted zarkon's. 
We are always hunting for more 

457
00:25:36,600 --> 00:25:38,200
locations with Heidi and 
zarkon's. 

458
00:25:38,300 --> 00:25:41,100
Do you have any promising leads 
at this point? 

459
00:25:41,300 --> 00:25:45,600
We haven't found any new 
locations, but we did some more 

460
00:25:45,600 --> 00:25:49,600
analysis on one location in 
India and one in Wyoming. 

461
00:25:50,000 --> 00:25:53,300
And here we know that people 
have found old Zircon. 

462
00:25:53,300 --> 00:25:56,000
So we went in and we are just 
trying to analyze thousands of 

463
00:25:56,000 --> 00:25:59,200
circles just to see how old can 
we get, how old is the oldest 

464
00:25:59,200 --> 00:26:01,900
Zircon going to be? 
And I'm happy to report. 

465
00:26:01,900 --> 00:26:03,500
We found 14. 
You hate Ian. 

466
00:26:03,600 --> 00:26:06,400
Zircons in India and at least 
one and Wyoming. 

467
00:26:07,500 --> 00:26:09,400
Now that your mom thank you very
much. 

468
00:26:09,700 --> 00:26:13,400
Thank you. 
For more about geology b, as 

469
00:26:13,400 --> 00:26:16,500
well as pictures and 
illustrations, that support this

470
00:26:16,500 --> 00:26:19,200
podcast, go to geology B.com.