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This is Jala, g b with all of us
trampled. 

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In a recent episode na jibun 
spoke about newly discovered 

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Zircon crystals that form during
the late hadean and early, 

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archean, when the Earth was 
between 500 million and a 

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billion years old, the zircons 
revealed information about 

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processes occurring in the 
earth's Nason crust, casting, 

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light on, when, and how modern 
day plate, tectonics may have 

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started. 
In this episode, we talk about a

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very different source of 
information about the LEF 

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namely, the abundances of noble 
gases occurring within 

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present-day basalts. 
It turns out that these can 

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probe the Earth's mantle and 
atmosphere even further back in 

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time to the first hundred 
million years of Earth history. 

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Sujoy. 
Mukhopadhyay leads a team of 

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researchers who have developed 
new techniques for measuring. 

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The abundances of noble gas 
Isotopes in a variety of earth 

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materials by combining the 
results of these measurements 

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with geochemical models. 
He has shed light on questions 

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about the very early Earth and 
Planet formation that have 

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challenged researchers for 
decades here. 

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We focus on one of these. 
Do any structures originating 

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from the very early Earth 
survive in today's. 

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Tall. 
Sujoy mukhopadhyay is Professor 

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of geochemistry at the 
University of California. 

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Davis, sujoy mukhopadhyay. 
Welcome to geology B. 

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Thank you, Oliver. 
I'm delighted to join you. 

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And I am really excited to chat 
with you. 

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How is it that we are able to 
use noble gases to probe the 

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very early Earth is it to do 
with the fact that they are 

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chemically inert? 
So yes, you're absolutely right.

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It is got to do with their 
chemical inertness. 

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So in that respect the keeper 
memory of these very early 

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events and likewise we can 
combine the variety of Isotopes 

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from the different noble gases 
to probe the Earth on different 

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time scales. 
The noble gases form a group in 

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the periodic table from Helium 
being the lightest through neon 

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argon Krypton Xenon and radon, 
how were these elements 

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produced. 
So in the Noble gases, we have 

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isotopes that we called 
primordial, which means these 

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are the Isotopes that were 
produced in stars and then the 

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solar system acquired these 
elements from neighboring stars.

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And then there are set of 
isotopes that are produced by 

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radioactive decay such as from 
elements, like, uranium and 

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thorium, and potassium. 
And the Really fascinating 

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aspect about this is that the 
half-lives of Of these isotopes 

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that ultimately end up producing
these noble. 

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Gases range from something like 
14, billion years, for thorium 

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all the way down to something 
like 16 million years for an 

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isotope of iodine that produces 
a particular isotope of xenon. 

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So, in many respects, this very 
wide range of these. 

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Half-lives, give us the sense to
Pro or it on these very 

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different time. 
Scales you focused on Particular

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isotope of xenon to probe the 
early Earth, and that was 129 

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Xenon. 
Can you explain why? 

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Yes. 
So 129 Xenon comes from the 

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radioactive decay of 129 iodine.
And this particular isotope was 

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present when the solar system 
formed, but it's Half-Life was 

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16 million years and typically 
the The useful range or useful 

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time range for any particular 
radioisotope is roughly six 

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times its Half-Life. 
So that means that after about 

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100 million years, I dine 129 is
no longer around. 

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All of, it has been converted to
129 Xenon. 

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So, therefore Earth is able to 
keep a memory of this 

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radioactive decay happening 
within the first 100 million 

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years, because After 100 million
years, there was not going to be

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any new production of 129 Xenon.
So any kind of variability that 

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people see on the Earth would 
have to relate back to this 

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first hundred million years. 
I said, in my introduction that 

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you can use such noble, gas, 
abundance, measurements to shed 

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light on whether today's mantle 
retains any of the original 

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structure from which it first 
differentiated, how do you 

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connect measurements of a Xenon 
isotopes? 

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Isotope with the mantle. 
So what we do is we start 

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probing the products of melting 
of the modern-day mantle. 

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So for example, if I go to 
places like Hawaii or Iceland 

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which are really nice places to 
visit on its own, but also 

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happened to be location of 
mantle plumes or hotspots. 

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And in these mantle plumes, we 
now have evidence from 

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seismology that there. 
Derived from Material very near 

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the core-mantle boundary. 
So, in that respect these plumes

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are acting as chemical probes of
the composition of the deepest 

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parts of the Earth's mantle and 
likewise, when we go to a 

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mid-ocean ridge spreading Center
where there is new oceanic crust

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being created the partial 
melting, that we see is being 

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derived from Material, that's 
present in the Shell or part of 

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the mantle. 
So then, bye. 

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Comparing the composition of 
basalts in the mantle, plumes 

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versus the composition of the 
salts from the mid-ocean ridge. 

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We're effectively probing 
different depth within the 

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Earth's mantle. 
And so if we see differences in 

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the 129 Xenon, composition 
between these two different 

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regions of the mantle, we can 
immediately say aha. 

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The system could have only 
changed within the first 100 

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million years. 
The fact that See, differences 

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are pointing to the fact that it
had to have come from that first

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100 million years. 
So that's how we connect our 

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measurements of mantle. 
Drive basalts to what's actually

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within the Earth's interior. 
That's fascinating, I'm struck 

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by the fact that you can 
actually measure the abundances 

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of noble gases in various kinds 
of battles. 

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So how do noble gases get into 
the Rock in the first place? 

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I mean being inert. 
They can't really form minerals 

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or react with the minerals. 
We in any way, can they you're 

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right? 
They can't really chemical you 

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react with the minerals and 
because of that, they don't 

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actually like to be in a mineral
because they are not forming any

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kind of chemical bond with their
neighboring constituents. 

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So often that tend to exist in 
what might be potentially 

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distorted sites within a mineral
lattice, or they might be 

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present in very large. 
Ring structure in certain Lines 

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of minerals like amphiboles but 
those sites are rare and because

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of that, they would rather be in
a liquid phase where there are 

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more opportunities for these 
noble gases to be present and 

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compared to liquid phase of 
vapor phase is their preferred 

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host because then they're really
happy. 

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So what happens is when the 
mantle starts partially melting 

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The noble gases are one of the 
first elements to leave the 

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mineral lattice and go into the 
Melt but there are other 

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elements other compounds such as
maybe CO2 or water. 

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Which also typically do not like
to be in minerals and want to 

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effectively go from the mineral 
to these males that are forming 

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as the parcel of mantle starts 
to rise to the surface, and the 

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pressure release causes this 
partial melting. 

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And then the male starts, Early 
rising to the very surface of 

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the Earth and as the mouth 
starts Rising ultimately, a CO2 

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Vapor bubble might form. 
And then the noble gases will 

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right away, go from the Melt, 
into the CO2 Vapor bubble. 

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And when this melt erupts onto 
the sea floor, it immediately 

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quenches because it is in 
contact with really cold ocean 

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water and it forms a class and 
then glass effectively 

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encapsulate, these Vapor bubbles
So, we then take these glass 

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samples into our laboratory, and
we crush them under vacuum and 

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release the vapor bubbles, which
releases the noble gases. 

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And that's what we end up 
measuring in our laboratory. 

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That's fascinating that they 
come out into the gas phase, but

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that makes me wonder. 
Why did these noble gases go 

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into the solid phase at all, to 
begin with. 

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When the earth was formed, why 
didn't they just all stay in an 

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atmosphere? 
That's a really fascinating 

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question, and we can kind of 
speculate as to why Why? 

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So in the earlier that at some 
point there was a magma ocean 

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where maybe most of the mantle 
was molten. 

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And then this magma ocean will 
eventually D gas to form the 

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very earliest atmosphere and the
noble gases are going to 

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partition between this magma 
Ocean and the atmosphere but 

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there are solubility in this 
magma is very low but it's not 

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zero. 
So there's still going to be a 

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finite amount. 
That is going to be in the 

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magma. 
The ocean. 

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And then, as the planet cools by
losing heat, to space the magma,

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ocean is going to slowly start 
to crystallize. 

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And basically, the noble gases 
are prisoners at this point, 

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because as the minerals are 
forming, they are being shoved 

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into these minerals because they
can't escape. 

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So, they are present in very low
abundances in these melts. 

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And then, when the Melt starts 
to solidify the Enter or are 

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forced to enter the minerals. 
But again, in very low 

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abundances and so the first 
opportunity to get the try and 

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escape, and that first 
opportunity is re melting of the

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mantle. 
So, now we have these gas 

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bubbles, which are say in the 
case of the mid-ocean ridge. 

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Basalt Vex, spewing out onto the
sea floor, and in the case of 

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the ocean Islands, they're 
coming up in volcanoes like in 

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Hawaii. 
But in that point they must 

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start being affected by in one 
case contamination by seawater 

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and in the other case, 
weathering with the atmosphere 

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on the islands. 
So the atmosphere itself also 

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has some noble gases. 
We hear quite a bit about the 

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helium in the atmosphere and 
then we know that radon is 

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generated in our basement 
sometimes, if our houses are 

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built on granite. 
And we got to watch out for 

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that. 
Mmm. 

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So, do these gases, contaminate 
these gas bubbles, and how do 

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you get at the actual mantle of 
Vince's, so yes, this is one of 

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the frustrations that we have to
deal with in these measurements 

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that we often don't get a 
sample. 

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That is completely devoid of 
contamination of the atmospheric

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gases. 
And, as you point out, yes, when

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you rupt the basalt out, to the 
sea floor, they might get 

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contaminated by the ocean water,
which is some dissolved noble 

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gases in them for. 
Or the mantle plumes. 

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We also actually try and collect
the soil samples that erupt 

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underwater as opposed to the 
lavas that are up straight into 

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the atmosphere, sub-area lie. 
And the reason is that, if they 

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erupt underwater pressure, 
there's still a chance that the 

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gas bubbles would be trapped in 
the liquid itself. 

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Whereas if they erupt straight 
into the atmosphere, the chances

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are that the bubbles would be 
lost very quickly to Sphere and 

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be solidified, Basalt sample 
won't have a lot of gas bubbles,

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but independent of this, both 
the whom basalts and the 

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mid-ocean ridge basalts would 
have a little bit of atmospheric

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contamination. 
So, the way we try and tease 

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this out is by crushing the 
sample in multiple steps, 

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because the expectation is that 
they're going to be point so 

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weaknesses in these Salt 
samples, like fractures through,

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which the condemnation is going 
to enter the sample and so gas 

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bubbles, that might be close to 
microfracture, might actually 

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have a lot more of this 
atmospheric contamination, or as

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little tiny gas. 
Bubbles that are much further 

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away from the fractures may have
very little or none. 

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00:13:18,500 --> 00:13:23,200
So when we start cracking the 
sample open the first set of 

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00:13:23,208 --> 00:13:26,100
bubbles that would be released 
would The ones that are very 

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close to the fracture patterns 
because the samples would break 

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along these pre-existing Plains 
of weaknesses. 

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So typically what we see is, 
when we first start, crushing 

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the sample, most of the measured
noble, gas composition look 

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largely similar to what you 
would expect in seawater, which 

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is the atmospheric signature 
dissolved in seawater. 

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00:13:47,900 --> 00:13:52,500
And then as we progressively 
crack the sample into smaller 

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and smaller bits, we start to 
see the composition Isshin move 

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away from the atmospheric, 
composition towards the mantle 

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composition. 
And very interestingly, what we 

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find is that for both the 
mid-ocean ridge basalts and the 

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mantle plume resources start up 
at the same point in their 

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initial Crushers, which is the 
atmospheric composition. 

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But then, as we progressively 
crush the sample, the trend 

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starts diverging in two 
different directions, which are 

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indicated. 
That whatever composition is 

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being contaminated, it's not the
same. 

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Because if it was the same, both
sets of rocks, would have 

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defined a single or Trend 
because it would be a single 

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mantle composition contaminated 
by a single atmospheric 

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00:14:44,500 --> 00:14:47,800
composition. 
But we see two distinct Trends 

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and that's telling us there are 
two distinct sources within the 

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Earth's interior. 
How do you actually we measure 

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the noble gas abundances, you 
crush the basalt in a vacuum 

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chamber. 
And then how do you get the 

228
00:15:02,108 --> 00:15:04,700
abundance of a noble gas? 
I'm curious because it's so 

229
00:15:04,700 --> 00:15:07,600
inert. 
So, again, that's a fascinating 

230
00:15:07,600 --> 00:15:11,300
question. 
So, when we crush the basalt and

231
00:15:11,300 --> 00:15:15,900
we release the gas bubbles, most
of the gas is actually CO2 

232
00:15:16,800 --> 00:15:20,800
dissolved in that CO2 at the 
level of parts per trillion. 

233
00:15:20,800 --> 00:15:24,200
Parts for quadrillion are these 
noble gases. 

234
00:15:24,600 --> 00:15:29,200
So one of First things he have 
to do is to get rid of the CO2, 

235
00:15:29,200 --> 00:15:34,200
get rid of any nitrogen, any 
little bits of methane or water,

236
00:15:34,200 --> 00:15:37,900
that might be present. 
So the way we do this is we 

237
00:15:38,100 --> 00:15:43,700
expose all of the gases to a 
highly reactive surface and that

238
00:15:43,700 --> 00:15:46,900
highly reactive surface can be 
absorbs all of these 

239
00:15:47,500 --> 00:15:51,300
constituents like CO2 water 
nitrogen and so on but the noble

240
00:15:51,300 --> 00:15:55,100
gases are left behind because 
they're chemically inert and so 

241
00:15:55,200 --> 00:15:59,100
That's how we purify the noble 
gases and then we can separate 

242
00:15:59,100 --> 00:16:03,200
them out from each other. 
Using a very cold, cryogenic 

243
00:16:03,200 --> 00:16:07,300
trap where the noble gases, get 
trapped on to a metallic 

244
00:16:07,300 --> 00:16:10,200
surface. 
And then we progressively 

245
00:16:10,200 --> 00:16:13,900
increase the temperature of that
metal surface and that will 

246
00:16:13,900 --> 00:16:18,400
slowly release first helium and 
the neon and then are gone. 

247
00:16:18,400 --> 00:16:20,500
And so on. 
And so as one of the gases gets 

248
00:16:20,500 --> 00:16:24,600
released from this very cold, 
cryogenic trap, we take that gas

249
00:16:24,600 --> 00:16:28,400
and we put it To a mass 
spectrometer to measure how many

250
00:16:28,400 --> 00:16:31,000
atoms of helium we have. 
And what its isotopic 

251
00:16:31,000 --> 00:16:33,700
composition is and then we 
repeat it for all of the other 

252
00:16:33,700 --> 00:16:37,700
noble gases, like neon and argon
and Krypton and Xenon. 

253
00:16:38,100 --> 00:16:41,200
So, let's come back to the 
progressive crushing. 

254
00:16:41,200 --> 00:16:44,700
Then you start out with the 
first bubbles being essentially 

255
00:16:44,700 --> 00:16:48,300
reflective of are of the 
atmosphere, and then, as you 

256
00:16:48,300 --> 00:16:52,100
crush, more and more than 
abundance is diverge, until I 

257
00:16:52,100 --> 00:16:55,100
guess the very very last 
crushes. 

258
00:16:55,200 --> 00:16:59,700
Has are more reflective of the 
actual mantle abundances on the 

259
00:16:59,700 --> 00:17:04,700
one hand of mid-ocean ridge 
Basalt and on the other of ocean

260
00:17:04,800 --> 00:17:08,800
Island Basalt. 
So what do those results show? 

261
00:17:09,599 --> 00:17:16,599
So that's where this half-life 
of the parent radioisotope 

262
00:17:16,599 --> 00:17:22,200
iodine 129 comes in because what
we are detecting are these 

263
00:17:22,599 --> 00:17:27,400
different signatures of 129. 
Xenon in the ocean Island 

264
00:17:27,400 --> 00:17:32,500
basalts and in the middle should
enrich basalts and the 

265
00:17:32,500 --> 00:17:35,300
difference could be created in 
only two ways. 

266
00:17:35,500 --> 00:17:41,000
One is through differences that 
we are inherently present in the

267
00:17:41,000 --> 00:17:45,200
mantle early on because of 
differences in let's say the 

268
00:17:45,200 --> 00:17:49,200
degree of degassing of the 
Earth's interior or they might 

269
00:17:49,200 --> 00:17:53,300
be created by subduction of 
atmosphere. 

270
00:17:54,400 --> 00:17:56,300
And so what these He's two 
different Trends. 

271
00:17:56,300 --> 00:17:59,900
Tell us is that subduction of 
atmosphere. 

272
00:18:00,300 --> 00:18:05,900
Can't possibly explain this 
difference between the mid-ocean

273
00:18:05,900 --> 00:18:09,000
ridge basalts and the ocean 
Island basalts because they 

274
00:18:09,000 --> 00:18:12,100
don't lie on the same mixing 
Trend. 

275
00:18:12,700 --> 00:18:18,300
And so our only option in terms 
of an interpretation is that the

276
00:18:18,300 --> 00:18:24,700
differences in Xenon, 129 comes 
from the decay of iodine 129 in 

277
00:18:24,700 --> 00:18:30,500
the And as I pointed out 
initially in the podcast that 

278
00:18:30,900 --> 00:18:35,900
the iodine 129 is only around 
for the first hundred million 

279
00:18:35,900 --> 00:18:39,900
years of Earth's history. 
And so that means that, then 

280
00:18:39,900 --> 00:18:45,000
this difference in the Xenon 129
could only have been produced 

281
00:18:45,000 --> 00:18:47,300
within that first hundred 
million years. 

282
00:18:47,300 --> 00:18:51,500
And that's the maximum range, 
which of the two kinds of Basalt

283
00:18:51,500 --> 00:18:56,200
has the lower amount of xenon. 
John 1:29. 

284
00:18:56,400 --> 00:19:01,400
So it turns out that the lower 
amount of xenon 129 actually is 

285
00:19:01,400 --> 00:19:06,700
present in the Gloom mantle or 
the ocean Island Basalt mantle. 

286
00:19:06,800 --> 00:19:11,400
That's the one, then that 
retains an identity, that goes 

287
00:19:11,400 --> 00:19:13,800
all the way back to the first. 
100 million years of Earth 

288
00:19:13,800 --> 00:19:15,000
history. 
Is that right? 

289
00:19:15,400 --> 00:19:18,700
So that's right. 
We think that its identity is 

290
00:19:18,700 --> 00:19:23,000
related to its history within 
that first hundred million years

291
00:19:23,600 --> 00:19:27,600
and that it's telling us 
Something about the differences 

292
00:19:27,600 --> 00:19:32,300
in the degree of gas laws, from 
these two different regions of 

293
00:19:32,300 --> 00:19:35,800
the Earth's mantle. 
Because again, one critical 

294
00:19:35,800 --> 00:19:40,900
point to remember, is that Xenon
or any of the other noble gases,

295
00:19:41,300 --> 00:19:44,500
don't just Escape out of The 
Mantel on their own. 

296
00:19:44,900 --> 00:19:49,900
They usually are taking a ride 
on some other gas species like 

297
00:19:49,900 --> 00:19:56,400
CO2 or maybe water. 
So their history is Only tied to

298
00:19:56,400 --> 00:20:00,900
the history of these other gases
like carbon dioxide or water, 

299
00:20:01,300 --> 00:20:04,900
okay? 
So the ocean island, or the 

300
00:20:05,000 --> 00:20:09,300
basalt that we think was sampled
from much much deeper in the 

301
00:20:09,300 --> 00:20:13,200
earth than the mid-ocean ridge 
Basalt, which we think comes 

302
00:20:13,200 --> 00:20:18,300
from middle or perhaps upper 
levels of the mantle has less of

303
00:20:18,300 --> 00:20:21,200
the Xenon 129. 
And therefore, it is what 

304
00:20:21,200 --> 00:20:24,700
retains the memory of the very, 
very earliest formation of the 

305
00:20:24,700 --> 00:20:28,500
Earth. 
So does that tell us that in the

306
00:20:28,500 --> 00:20:33,800
mantle it has not in fact, 
experienced any mixing with the 

307
00:20:33,800 --> 00:20:36,800
material that forms the 
mid-ocean ridge Basalt. 

308
00:20:37,300 --> 00:20:41,400
I don't think it indicates that 
it has no mixing. 

309
00:20:41,900 --> 00:20:46,700
I think what it indicates is 
that it has a limited amount of 

310
00:20:46,700 --> 00:20:50,100
mixing or another way of saying 
it. 

311
00:20:50,100 --> 00:20:56,100
Is that after 100 million years,
the earth has Never been 

312
00:20:56,100 --> 00:20:59,200
homogenized. 
Because if it had been 

313
00:20:59,300 --> 00:21:03,600
homogenized such as by mixing, 
then we wouldn't see this 

314
00:21:03,600 --> 00:21:09,600
difference in Xenon 129 because 
once we homogenize it and mix 

315
00:21:09,600 --> 00:21:13,900
away this difference after 100 
million years, I don't have a 

316
00:21:13,900 --> 00:21:16,500
mechanism. 
Now to regenerate the 

317
00:21:16,508 --> 00:21:19,900
difference. 
So the way I think about it is 

318
00:21:19,900 --> 00:21:24,900
that yes there has been mixing 
between the mid-ocean ridge. 

319
00:21:25,300 --> 00:21:28,900
Called source and the ocean 
Island Basalt Source but it's 

320
00:21:28,900 --> 00:21:33,600
limited. 
So if I was able to dial Back 

321
00:21:33,600 --> 00:21:38,100
Time all the way back to 4.4 
billion years, I would predict 

322
00:21:38,100 --> 00:21:42,100
that the differences that I see 
compared to today would have 

323
00:21:42,100 --> 00:21:46,300
been much, much larger. 
And so over time that difference

324
00:21:46,300 --> 00:21:49,400
is being whittled away by 
mixing, but it has not been 

325
00:21:49,400 --> 00:21:53,800
erased. 
So, how might such a separate 

326
00:21:53,800 --> 00:21:57,100
Source material at the bottom? 
Bottom of the mantle of formed 

327
00:21:57,400 --> 00:22:00,900
so early on and maintained. 
Its separate identity at least 

328
00:22:00,900 --> 00:22:04,500
in part throughout four and a 
half billion years of Earth's 

329
00:22:04,500 --> 00:22:07,300
history. 
So that is one of the million 

330
00:22:07,300 --> 00:22:13,400
dollar questions and one 
potential mechanism. 

331
00:22:13,400 --> 00:22:18,300
For creating these differences 
might be related to Earth's 

332
00:22:18,500 --> 00:22:24,300
violent birth where the planet 
was being bombarded by other 

333
00:22:25,000 --> 00:22:27,700
end. 
Heroes are protoplanets 

334
00:22:27,700 --> 00:22:33,600
generating very deep magma, 
oceans and more recent Studies 

335
00:22:33,600 --> 00:22:37,800
have shown that one of the 
products of crystallization of 

336
00:22:37,800 --> 00:22:44,600
these mag motions could be iron 
and magnesium Rich phases which 

337
00:22:44,600 --> 00:22:48,600
settled to the bottom of the 
mantle and those phases. 

338
00:22:48,600 --> 00:22:52,800
Now are going to be inherently 
denser than the rest of the 

339
00:22:52,800 --> 00:22:58,400
mantle so one could imagine in a
scenario where there was a giant

340
00:22:58,400 --> 00:23:03,500
impact during Earth's growth 
that melted the planet may be 

341
00:23:03,500 --> 00:23:07,600
all the way down to the 
core-mantle boundary and you 

342
00:23:07,600 --> 00:23:10,600
crystallized this iron and 
magnesium Rich layer which was 

343
00:23:10,600 --> 00:23:15,900
inherently denser and then 
subsequent magma, oceans created

344
00:23:15,900 --> 00:23:20,700
by other impacts never reached 
down to that depth and so that 

345
00:23:20,700 --> 00:23:26,600
inherently denser material has 
effectively survived All through

346
00:23:26,800 --> 00:23:29,900
the planets history. 
So that's one potential 

347
00:23:29,900 --> 00:23:33,600
explanation. 
I don't think we have a definite

348
00:23:33,700 --> 00:23:40,400
answer at this point to how 
exactly this Reservoir was 

349
00:23:40,400 --> 00:23:43,100
produced. 
And I think that is one of the 

350
00:23:43,100 --> 00:23:48,000
challenges in terms of figuring 
out, how did we produce it? 

351
00:23:48,000 --> 00:23:51,500
And why is it still around for 
such a long time? 

352
00:23:51,500 --> 00:23:55,100
Why didn't later giant impacts 
such as Maybe? 

353
00:23:55,200 --> 00:23:58,200
Be the moon forming, giant 
impact, wipe this out. 

354
00:23:58,400 --> 00:24:02,300
It's reminds me of a couple of 
earlier podcasts in which two 

355
00:24:02,300 --> 00:24:04,700
speakers. 
In fact, I'm and McNamara. 

356
00:24:04,700 --> 00:24:09,000
And Matt Jackson and particular 
spoke about these very large 

357
00:24:09,000 --> 00:24:11,800
structures. 
We see, when we make seismic 

358
00:24:11,800 --> 00:24:15,600
images of the earth that called 
large low Shear, velocity 

359
00:24:15,600 --> 00:24:19,900
provinces, where it appears that
the shear waves are traveling, a

360
00:24:19,908 --> 00:24:23,900
little bit slower, which one can
interpret because they're little

361
00:24:23,900 --> 00:24:27,000
warmer than the surrounding. 
Ring or alternatively or maybe 

362
00:24:27,000 --> 00:24:29,400
better both of their made of a 
different material. 

363
00:24:29,800 --> 00:24:32,300
Is it possible that these 
reservoirs that you're talking 

364
00:24:32,300 --> 00:24:35,900
about that have the separate 
identity correspond to these 

365
00:24:36,000 --> 00:24:39,300
large low, Shear wave velocity 
provinces that we can actually 

366
00:24:39,300 --> 00:24:42,600
see. 
So, most likely the answer to 

367
00:24:42,600 --> 00:24:47,800
that is, yes, because again, as 
we look at recent, seismic, 

368
00:24:47,800 --> 00:24:50,500
evidences. 
We see that these ocean Island, 

369
00:24:50,500 --> 00:24:55,000
besides these mantle, plumes are
being derived from these low. 

370
00:24:55,200 --> 00:24:59,900
Whoa, large Shear wave velocity 
provinces, and I'm of the group 

371
00:24:59,900 --> 00:25:03,200
that actually believes that 
these large, no Shear wave 

372
00:25:03,200 --> 00:25:06,000
velocity. 
Provinces are not just warmer 

373
00:25:06,000 --> 00:25:09,000
that they're actually also 
denser than the surrounding 

374
00:25:09,000 --> 00:25:12,200
mantle. 
And so they're not made out of 

375
00:25:12,300 --> 00:25:17,100
entirely material that have 
existed in its pristine form, 

376
00:25:17,100 --> 00:25:21,800
for over four and a half billion
years, but they have at least 

377
00:25:21,800 --> 00:25:25,100
chunks of material that go all 
the way back. 

378
00:25:25,200 --> 00:25:29,200
Back to this 4.5 billion years, 
but there might be other 

379
00:25:29,200 --> 00:25:33,000
material that has been 
recirculated from the surface 

380
00:25:33,100 --> 00:25:35,800
into these, large low, Shear 
wave, velocity provinces. 

381
00:25:35,800 --> 00:25:38,500
And we actually do see some 
chemical evidence that that has 

382
00:25:38,500 --> 00:25:42,300
happened and have people built 
Judah, Dynamic models. 

383
00:25:42,700 --> 00:25:45,200
And I think Alan McNamara showed
some of that with the 

384
00:25:45,200 --> 00:25:49,600
simulations that he did. 
That can generate stable 

385
00:25:49,700 --> 00:25:52,300
patterns that are consistent 
with what we know about how 

386
00:25:52,300 --> 00:25:55,000
slabs subduct and sink to very 
great. 

387
00:25:55,200 --> 00:25:58,800
Depths and then possibly 
recycled from somewhere in quite

388
00:25:58,800 --> 00:26:00,700
far down near the core-mantle 
boundary. 

389
00:26:01,300 --> 00:26:05,100
So, yes, I think Alan's work 
actually do show that these 

390
00:26:05,100 --> 00:26:10,900
features could be stable for the
entire time of Earth's history 

391
00:26:10,900 --> 00:26:13,100
of about four and a half billion
years and there are other groups

392
00:26:13,100 --> 00:26:17,800
that are likewise shown that. 
But I'm not sure this point 

393
00:26:17,800 --> 00:26:22,700
there is a general consensus 
that these provinces which are 

394
00:26:22,700 --> 00:26:26,500
maybe a little bit bigger than 
the size of Let's continents on 

395
00:26:26,500 --> 00:26:29,600
the surface actually, go all the
way back to four and a half 

396
00:26:29,600 --> 00:26:32,000
billion years. 
There's another group of thought

397
00:26:32,000 --> 00:26:36,700
that says these are created 
entirely through subduction of 

398
00:26:36,700 --> 00:26:40,200
earth's tectonic plates. 
But now we know that can't 

399
00:26:40,200 --> 00:26:42,600
really be the case, right? 
Because of the work you just 

400
00:26:42,600 --> 00:26:44,200
described. 
That's correct. 

401
00:26:44,200 --> 00:26:48,500
So I would argue that when we 
put together the seismic 

402
00:26:48,500 --> 00:26:52,600
evidence that these mantle 
plumes are coming from these 

403
00:26:52,600 --> 00:26:54,900
large low, Shear wave velocity 
provinces. 

404
00:26:55,300 --> 00:26:59,500
With the Xenon composition that 
is different between mid-ocean 

405
00:26:59,500 --> 00:27:02,000
ridge basalts and these ocean 
Island basalts. 

406
00:27:02,300 --> 00:27:06,100
I would say there must be a 
component in this material that 

407
00:27:06,100 --> 00:27:08,900
has to go all the way back to 
four and a half billion years. 

408
00:27:09,100 --> 00:27:14,200
It doesn't rule out that maybe 
the vast majority is recycled 

409
00:27:14,700 --> 00:27:20,300
but there is chunks of material.
That is really really old. 

410
00:27:20,900 --> 00:27:24,600
I'm struck by the coincidence 
that there happens to be. 

411
00:27:25,600 --> 00:27:29,800
Noble gas, radiogenic isotopes. 
That was produced on a time 

412
00:27:29,800 --> 00:27:33,200
scale, that's very short 
compared to the age of the Earth

413
00:27:33,700 --> 00:27:38,200
but still the order of time over
which geodynamic or processes 

414
00:27:38,200 --> 00:27:41,200
can occur. 
IE a few tens of millions of 

415
00:27:41,200 --> 00:27:44,300
years. 
That is what enables us to 

416
00:27:44,300 --> 00:27:48,300
distinguish a reservoir that was
isolated during a Time less than

417
00:27:48,300 --> 00:27:51,400
a few half-lives of the 
corresponding Decay. 

418
00:27:51,400 --> 00:27:55,600
I so early on in Earth, history,
are there any other Hopes, whose

419
00:27:55,600 --> 00:27:58,800
abundances we can measure that 
are produced by radiogenic. 

420
00:27:58,800 --> 00:28:02,900
Decay was still shorter 
half-lives specifically half 

421
00:28:02,900 --> 00:28:06,600
live shorter than about 10 
million years which might enable

422
00:28:06,600 --> 00:28:09,400
us to probe still closer to the 
formation of the earth. 

423
00:28:10,100 --> 00:28:15,300
So yes, there are and one of 
these Isotopes is hafnium 182 

424
00:28:15,900 --> 00:28:20,600
which decays to tungsten 182. 
And this system is particularly 

425
00:28:20,600 --> 00:28:24,400
interesting because hafnium 
likes being in the mantle 

426
00:28:24,800 --> 00:28:28,200
tongue. 
In the Decay product likes being

427
00:28:28,200 --> 00:28:32,000
in the corps. 
So hafnium, tungsten has been 

428
00:28:32,000 --> 00:28:37,600
used extensively to look at the 
differentiation between a 

429
00:28:37,600 --> 00:28:41,300
planet's metallic core and its 
silicate mantle. 

430
00:28:42,100 --> 00:28:46,000
And interestingly, there are 
some recent studies now that 

431
00:28:46,000 --> 00:28:49,700
show that there are differences 
in tungsten isotopic, 

432
00:28:49,700 --> 00:28:54,400
composition between ocean Island
basalts and mid-ocean ridge 

433
00:28:54,400 --> 00:28:57,300
basalts. 
And again this is an indication 

434
00:28:57,300 --> 00:29:02,200
that that signature might have 
been created within the time 

435
00:29:02,200 --> 00:29:07,400
scale that hafnium was alive and
because the half-life of hafnium

436
00:29:07,400 --> 00:29:12,100
is shorter than iodine, 129 the 
half life is about 8.9 million 

437
00:29:12,100 --> 00:29:14,400
years. 
The total amount of time 

438
00:29:14,400 --> 00:29:18,200
available is 60 million years 
and now there is some growing 

439
00:29:18,200 --> 00:29:23,200
debate as to what might be the 
implication of this tungsten 

440
00:29:23,200 --> 00:29:26,700
isotope difference between ocean
Alan Basalt in mid-ocean ridge 

441
00:29:26,700 --> 00:29:33,300
basalts and could it potentially
also be an indicator of a 

442
00:29:33,300 --> 00:29:39,100
chemical interaction between the
Earth's core and its silicate 

443
00:29:39,100 --> 00:29:43,700
mantle because the core-mantle 
boundary is a fascinating 

444
00:29:43,700 --> 00:29:45,500
region. 
It's probably one of the most 

445
00:29:45,500 --> 00:29:48,200
reactive boundaries we have on 
the earth. 

446
00:29:48,200 --> 00:29:53,000
It is super hot and on one side 
we have pure iron metal or iron 

447
00:29:53,000 --> 00:29:55,000
metal with a little bit of 
other. 

448
00:29:55,100 --> 00:29:57,200
Tough. 
And on the other side we have 

449
00:29:57,300 --> 00:29:59,400
silicate material so one should 
expect that. 

450
00:29:59,400 --> 00:30:01,900
There are some chemical 
reactions that are ongoing. 

451
00:30:02,800 --> 00:30:06,700
And there are other Isotopes 
such as Palladium which the case

452
00:30:06,700 --> 00:30:08,800
to Silver. 
The half-life associated with 

453
00:30:08,800 --> 00:30:11,400
that is even shorter six and a 
half million years. 

454
00:30:11,900 --> 00:30:15,500
There is an isotope of Manganese
manganese 53 that decays to 

455
00:30:15,500 --> 00:30:19,600
chromium that has a half-life of
three million years and recently

456
00:30:19,600 --> 00:30:23,500
this manganese chromium system 
was utilized to look at the 

457
00:30:23,500 --> 00:30:25,000
time. 
Scales of magma ocean. 

458
00:30:25,100 --> 00:30:28,700
Crystallization for Mars. 
So there are other isotopes that

459
00:30:28,700 --> 00:30:32,100
might allow us to probe the 
Earth's formation much further 

460
00:30:32,100 --> 00:30:36,900
back in time and one of the wave
forward in my view is to 

461
00:30:36,900 --> 00:30:41,700
actually make all of these 
measurements on the same set of 

462
00:30:41,700 --> 00:30:44,600
samples. 
So we can build a much more 

463
00:30:44,900 --> 00:30:47,400
complete picture of what might 
be going on. 

464
00:30:47,700 --> 00:30:51,000
So, so far, we are still 
measuring these different 

465
00:30:51,000 --> 00:30:54,800
isotopes on different samples. 
So we are not necessarily always

466
00:30:55,100 --> 00:30:58,200
comparing an apple to an Apple. 
It might be an apples to oranges

467
00:30:58,200 --> 00:31:00,900
comparison. 
I'd like to ask you final 

468
00:31:00,900 --> 00:31:04,800
question. 
If you could command a limitless

469
00:31:04,800 --> 00:31:09,900
budget for either space-based or
terrestrial Research into the 

470
00:31:09,900 --> 00:31:12,400
early Earth, how would you use 
it? 

471
00:31:13,000 --> 00:31:17,300
So, I think I would design a 
mission to a comet to bring some

472
00:31:17,300 --> 00:31:21,100
Comet samples back to Earth, so 
we can study comments in much 

473
00:31:21,100 --> 00:31:24,600
more detail. 
And the reason I say that is 

474
00:31:24,600 --> 00:31:28,700
because I'm fascinated by the 
question of what was the 

475
00:31:28,700 --> 00:31:32,000
composition of the early 
atmosphere and where did the 

476
00:31:32,000 --> 00:31:36,900
early atmosphere come from? 
So in the noble gases we now see

477
00:31:36,900 --> 00:31:41,100
evidence that shows that the 
Earth's early atmosphere cannot 

478
00:31:41,100 --> 00:31:46,200
be generated simply by 
outgassing of its interior, but 

479
00:31:46,200 --> 00:31:51,300
we also don't have a meteorite, 
or a carbonaceous chondrite 

480
00:31:51,300 --> 00:31:56,100
necessarily that we can put our 
finger on say That particular 

481
00:31:56,100 --> 00:32:00,500
meteorite has all of the 
necessary characteristics that 

482
00:32:00,500 --> 00:32:03,400
can explain the atmospheric 
fingerprint. 

483
00:32:04,300 --> 00:32:07,800
And so the noble gases are 
extremely useful in terms of 

484
00:32:07,800 --> 00:32:11,600
fingerprinting, what kind of 
materials might have contributed

485
00:32:11,600 --> 00:32:15,100
to the early atmosphere? 
And if we know that we have a 

486
00:32:15,100 --> 00:32:19,200
much better sense of what the 
overall composition of the 

487
00:32:19,200 --> 00:32:21,200
atmosphere might have been in 
terms of. 

488
00:32:21,200 --> 00:32:24,900
Was it CO2 dominated or was it a
CO dominated? 

489
00:32:25,100 --> 00:32:28,200
Here, what was the proportion of
hydrogen in the atmosphere 

490
00:32:28,200 --> 00:32:31,900
compared to H 2 O. 
And so we know, so little of 

491
00:32:31,900 --> 00:32:34,800
commentary noble gases and 
comments in general, I would 

492
00:32:34,800 --> 00:32:37,100
argue that that's where I 
believe. 

493
00:32:37,100 --> 00:32:39,600
I would focus. 
My attention is to bring a 

494
00:32:39,608 --> 00:32:42,300
little bit of a comment back to 
my laboratory. 

495
00:32:42,500 --> 00:32:45,000
Do you have your eye on any 
specific comments that are 

496
00:32:45,000 --> 00:32:48,000
likely to come into our solar 
neighborhood anytime soon? 

497
00:32:48,300 --> 00:32:51,600
I cannot give you a direct 
answer in terms of a specific 

498
00:32:51,600 --> 00:32:54,900
comment other than that we would
want. 

499
00:32:55,000 --> 00:32:58,100
To sample. 
Both the icy part of the Comet 

500
00:32:58,100 --> 00:33:01,000
as well as the rocky part of the
Comet. 

501
00:33:01,100 --> 00:33:05,100
So a lot of our observations, so
far of comets are actually from 

502
00:33:05,100 --> 00:33:09,400
the icy part which supplements 
as the Comets come into the 

503
00:33:09,400 --> 00:33:13,900
inner solar system, we have very
little information about the 

504
00:33:14,200 --> 00:33:16,000
rocky part. 
We do have some amount of 

505
00:33:16,008 --> 00:33:20,100
material that was returned by 
the Stardust Mission but not 

506
00:33:20,100 --> 00:33:23,100
enough for somebody like me to 
make very precise measurements 

507
00:33:23,100 --> 00:33:26,700
of all of the noble gases. 
Sujoy mukhopadhyay. 

508
00:33:26,800 --> 00:33:28,700
Thank you very much. 
Thank you. 

509
00:33:28,700 --> 00:33:31,000
All of our for having me. 
This was wonderful. 

510
00:33:31,000 --> 00:33:35,400
It was a delight chatting with 
you for more about geology b, as

511
00:33:35,400 --> 00:33:38,500
well as pictures and 
illustrations that support this 

512
00:33:38,500 --> 00:33:41,100
podcast, go to geology B.com