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This is geology B with Oliver's 
trampled in previous, geology B 

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episodes. 
We've talked about using the 

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radioactive decay of uranium to 
lead within a Zircon, Crystal to

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infer the age of a rock, but the
Decay process also produces 

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another product helium being a 
gas and much more volatile than 

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led the helium diffuses out of 
the Zircon Crystal, even after 

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it. 
Eliza's. 

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So while the lead becomes 
trapped within the Zircon, as 

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soon as it forms within a 
cooling magma at 900 degrees 

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Centigrade, the magma has to 
cool all the way down to 200 

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degrees before. 
The Zircon can stop the helium 

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that is produced from leaking 
out of its crystal. 

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Lattice by looking at different 
Decay products of uranium. 

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We can measure how long ago the 
rock cooled to the temperature 

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at which each product became 
trapped in a mineral crystal and

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so obtain, multiple data points 
of the Rock's cooling history, 

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Becky flowers is a professor of 
geological Sciences at the 

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University of Colorado Boulder. 
She has a thermal chronology lab

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in, which he measures the 
amounts of the different 

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radioactive decay products 
within crystals to figure out 

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the cooling history of rocks, 
knowing how rocks cooled gives 

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us new insights on jalaja call 
histories and processes of many 

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parts of the earth. 
And even of the Moon, Becky 

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flowers, welcome to geology B. 
It's for having me. 

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It's a pleasure to be here. 
Why is it so valuable to 

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decipher the thermal histories 
of rocks? 

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What can we learn that other 
observations? 

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Don't tell us. 
So thermal histories can yield 

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really important constraints on 
the timing duration and rates of

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a whole array of Earth 
processes. 

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Because so many of these 
processes are either temperature

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dependent or influence 
temperature. 

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So for example, these include 
burial erosion magnetism 

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metamorphism and deformation 
Shen. 

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So I could just give you one 
example for erosion. 

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So because temperatures increase
with depth beneath the earth's 

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surface, a rock sitting at 3 
kilometers. 

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Deep in the earth is at warmer 
temperatures. 

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It's hotter than a rock sitting 
at the surface. 

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So as rocks approach, the 
Earth's surface due to removal 

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of overlying rocks by erosion. 
That rock will cool off. 

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So if we can reconstruct the 
cooling history of that rock, 

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that's a proxy for the erosion 
history of that rock and that 

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Turn can give us some insights 
into Vigor Earth processes such 

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as when a mountain belt with 
elevated or win a big canyon. 

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Like the Grand Canyon was in 
size and that in turn can give 

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us some insights into the 
processes that might have caused

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those events. 
Okay? 

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Before we talk about the 
applications of thermal 

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chronology to various geological
problems, I want to ask you 

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about the methods themselves. 
In the classic dating of zircon.

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Crystals, the daughter nuclide 
whose abundance is measured is 

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lead but in your lab you 
concentrate on a very much 

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lighter and more volatile 
daughter nuclide helium. 

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Why is that? 
Yes, we're in a deep constrains 

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mineral cooling rather than the 
crystallization age of a 

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mineral. 
We call this Thermo chronology 

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and the technique that I use 
uranium thorium helium is based 

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on the decay of uranium and 
thorium to heal him. 

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So, when in uranium and thorium,
they also undergo a long Decay 

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chain to lead. 
And in that process, they have a

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bunch of alpha decay events, and
those Alpha decays generate 

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alpha particles, which are 
helium atoms. 

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And so, in our technique, rather
than dating, the lead atoms, we 

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date the parent, uranium, 
thorium, as well as the helium 

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atoms. 
In the case of the uranium-lead 

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method in Zircon, the lead when 
it's produced is stuck in the 

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crystal ever since its produced.
So if you date a Crystal Zircon 

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with uranium Ledger essentially,
dating the crystallization age 

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of that mineral in contrast in 
the case of helium helium is an 

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element that is prone to 
diffusion out of the crystal. 

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So although if you're Zircon 
crystallizes and it's undergoing

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Decay and generating helium 
atoms, if that Zircon is at 

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elevated temperatures in the 
crust that helium will 

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completely diffuse out of the 
crystal. 

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So if you went and were able to 
date a crystal sitting down in 

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the Earth at 600 degrees C, you 
would get a zero age for that 

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Crystal. 
There's no healing retained in 

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it. 
And so it's only after that 

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mineral has cooled through a 
certain temperature known as the

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closure temperature and begins 
retaining helium. 

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That it begins to retain that 
daughter. 

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And so if you go and date that 
mineral in a cooling only 

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scenario, you date the time that
that mineral last cooled through

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its closure temperature and that
closure temperatures, much lower

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than the closer temperature of 
the lead, because the helium 

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diffuses out so much more easily
than if you like the crystal 

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lattice has to kind of close up 
a whole lot more to stop it 

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leaking out. 
Yeah, that's exactly the idea 

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and you can go and work on a 
single Crystal of zircon and you

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can get a uranium-lead date and 
date. 

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It's crystallization age. 
Let's say it's 100 million years

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ago and then you could also get 
uranium thrown helium date for 

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that same crystal and it might 
be a younger date. 

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That might tell us that that 
rock cooled and was exhuming and

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eroding to the surface. 
Much more recently what minerals

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are suitable for the uranium 
thorium helium from Akron. 

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G that you do one of the reasons
why this technique is so 

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versatile? 
Is that pretty much any mineral 

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that has Trace Amounts of 
uranium and Thorium in the 

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crystal structure, has the 
potential to be used as a 

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uranium thorium helium thermal 
chronometer is long as it's 

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retentive to helium. 
So, most Studies have used 

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appetite and Zircon because 
these are very common minerals 

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in many rock types. 
And they constrain thermal 

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histories at upper crustal and 
near surface conditions. 

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And so they're very useful for 
constraining. 

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Or Surface erosion histories, 
but there are a variety of other

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minerals that people are 
developing as helium thermal 

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chronometers and there's a bunch
of reasons for this. 

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One thing is that if you have 
lots of different minerals that 

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you can date from a single Rock 
and these different minerals, 

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have different closure 
temperatures, this allows you to

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reconstruct really high 
resolution thermal histories. 

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The second thing is that 
different rocks, have different 

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minerals in them. 
So it's useful to have tools 

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that allow us to reconstruct 
thermal histories in a whole 

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range of rock types. 
And then the third thing is that

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commonly, there is a desire to 
date processes that are 

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notoriously difficult to date, 
like weathering, which occurs at

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the Earth's surface and is 
climatically driven, and there's

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some minerals that we can date 
with helium, that allow us to 

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constrain some of these 
difficult to date. 

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Earth processes, and what's 
awesome. 

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These other minerals apart from 
zakone, appetite the iron oxides

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hematite and grew tight, because
there's are, commonly weathering

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products. 
They develop for example, soil. 

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Files. 
So in that case if you have a 

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mineral that develops at the 
Earth's surface and you date it,

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you might be constraining the 
time at which that mineral form 

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and be dating a weathering 
event. 

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Sometimes those minerals form on
fault surfaces. 

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And so there's a lot of 
innovative work that some groups

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are doing to constrain the 
timing of fault Movement by 

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dating hematite on these fault 
surfaces. 

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There are also other minerals 
like perovskites and badly. 

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I that occur in rocks that are 
mafic, rocks, iron and magnesium

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retracts that are other Is 
difficult to date there's 

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probably like 20 or 30 different
minerals that people have tried 

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to date with this tool with 
varying success in some of them 

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show. 
A lot of promise, I know that a 

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big part of your research effort
is directed to improving. 

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The thermal chronology methods. 
Not only to extend them to a 

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wider range of source rocks, but
also to make the results more 

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reliable and perhaps more 
precise. 

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Can you tell us what the main 
challenges are that you face 

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when you try and do that? 
Yes, I think one of the big 

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challenges that workers in this 
field are addressing right now, 

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is trying to better understand 
how helium, diffusion occurs in 

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different mineral phases. 
So as I was just talking about, 

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you have this healing that's 
generated and then it diffuses 

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out of the crystal in order to 
interpret those data 

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quantitatively, you need to know
the conditions under which the 

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helium diffuses out of your 
mineral and some minerals like 

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appetite and Zircon, the 
diffusivity of helium out of 

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your Crystal, how fast it goes 
out. 

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Is a function of not only 
temperature, which is what we 

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just talked about the things 
like radiation damage. 

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So as helium is generated, it's 
generated by radioactive decay 

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and that process damages, the 
Crystal and that affects the 

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Reit entity of your Crystal. 
Also Crystal size can affect the

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Reit entity or the diffusivity 
of helium out of your Crystal. 

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And so, there's a lot of work 
focused on trying to understand 

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these different mineral 
characteristics that control the

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loss of helium and to quantify 
those into A models. 

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So that we can have kinetic 
models that we can use to 

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decipher the significance of our
date. 

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I guess, in the idealized case, 
you'd have a function, which 

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should give you the diffusivity 
as a function of temperature, 

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radiation damage and Crystal 
size. 

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Yes, that's exactly what you 
want. 

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That's exactly what you want. 
But isn't it also further 

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Complicated by the fact that 
when you get A rock sample into 

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your lab. 
You're actually looking at that 

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time integration of all the 
diffusion out of that Crystal 

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over the geological time. 
So how do you that's another 

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issue, isn't it? 
Yeah. 

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So if you have proper kinetic 
models, you can deal with that, 

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but that's a great point. 
One simple way that we think 

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about it is that if you have a 
fast cooling history at 

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temperatures above the closure 
temperature, your helium is 

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completely lost from the 
crystal, okay? 

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And below that temperature, your
helium is completely retained. 

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And that's if you have like a 
fast cooling history and that's 

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envisioning. 
The system is like a light 

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switch. 
It's either on or it's off but 

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in reality it's not like that. 
It's like a dimmer switch. 

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So there's actually a 
temperature range over which 

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your helium can be partially 
retained in and partially lost 

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from the crystal. 
So, if you have a simple 

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scenario, let's say you're 
sitting in the Himalayas and 

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there's a granite that was in 
place 25 million years ago, and 

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then it gets rapidly eroded and 
brought to the surface. 

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That's pretty simple, your date 
is simply. 

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We going to record when that 
rock was eroded and got to the 

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surface. 
However, because of this 

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temperature window over which 
helium is partially retained and

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partially lost, you can have 
much longer histories that 

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involve erosion to the surface 
reburial and then erosion back 

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to the surface. 
And over that entire history, 

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your Crystal may be gaining 
helium and then losing a little 

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bit and then regaining it. 
And so this requires them 

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thinking about some of these 
so-called dates that we Obtained

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for a minerals, actually or 
something, a reflection of the 

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total time, integrated history, 
of helium, accumulation and 

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diffusion out of your Crystal. 
These require quantitative 

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models and increasingly our 
field is pushing towards looking

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at deeper time histories to 
infer their own erosion 

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histories over longer time 
scales. 

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And that's something that my 
group does quite a bit of work 

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on. 
Let's talk now about some of the

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geological problems that you've 
addressed. 

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Seeing Thermo chronology. 
Let's start with a great 

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unconformity. 
Yeah, the great unconformity. 

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So this is an iconic geologic 
feature. 

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It marks a major Gap in the 
geological record of the 

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continents. 
So it classically marks. 

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This nice sharp boundary in the 
Rock record between unfossilized

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first pre-cambrian, Brock. 
So much older rocks and 

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fossiliferous layered 
sedimentary rocks and across 

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that. 
Andre at the great unconformity 

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there's commonly a half billion 
years up to like three billion 

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years of missing time. 
The great unconformity was 

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00:12:09,600 --> 00:12:13,200
originally described that its 
famous Grand Canyon locality by 

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John Wesley Powell. 
But this feature occurs all over

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the US you can go out and see it
at all kinds of locations around

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the United States and also 
occurs all around the world. 

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And to Charles Darwin, he talked
about the sudden appearance of 

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complex macroscopic fossils in 
the Cambrian strata. 

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00:12:30,500 --> 00:12:33,300
The great unconformity is 
suggesting some kind of singular

231
00:12:33,300 --> 00:12:36,600
Global event that led to the 
development of this feature and 

232
00:12:36,600 --> 00:12:39,700
this missing Gap in time. 
And so Rosen, across this 

233
00:12:39,700 --> 00:12:43,600
feature, it's played a big role 
in ideas about the Cambrian 

234
00:12:43,600 --> 00:12:46,200
explosion of Life. 
Some people have tried to 

235
00:12:46,200 --> 00:12:49,200
develop a causal link between 
major erosion across the Great 

236
00:12:49,200 --> 00:12:52,300
unconformity. 
And the Cambrian diversification

237
00:12:52,300 --> 00:12:55,700
of life, we actually don't 
really know how old it is. 

238
00:12:56,200 --> 00:12:58,500
So we know the age of 
sedimentary rocks that sit above

239
00:12:58,500 --> 00:13:02,100
this feature, but Until recently
we haven't been able to 

240
00:13:02,100 --> 00:13:06,700
constrain the timing of the 
erosion event that led to the 

241
00:13:06,700 --> 00:13:09,600
development of that erosion 
surface and that's exactly 

242
00:13:09,600 --> 00:13:12,200
because this feature marks is 
huge gap. 

243
00:13:12,300 --> 00:13:16,100
In the Rock record so the 
erosion history that led to its 

244
00:13:16,100 --> 00:13:18,600
development, you can't 
investigate that directly by 

245
00:13:18,600 --> 00:13:22,500
study of preserved, Rock units. 
So this is something that we can

246
00:13:22,500 --> 00:13:27,100
tackle with firmer chronology. 
A number of models have been 

247
00:13:27,100 --> 00:13:31,000
proposed for when and why the 
Great unconformity The some 

248
00:13:31,000 --> 00:13:33,800
models have suggested the great 
unconformity formed right at the

249
00:13:33,800 --> 00:13:37,600
timing of the Cambrian explosion
and others will it occurred 500 

250
00:13:37,600 --> 00:13:41,000
million years before that and so
if it occurred for 500 million 

251
00:13:41,000 --> 00:13:43,800
years before that it probably 
doesn't have a direct causal 

252
00:13:43,800 --> 00:13:48,800
link and so to actually try to 
understand degrade and conformed

253
00:13:48,800 --> 00:13:51,500
erosion, contribute to the 
Cambrian explosion, we actually 

254
00:13:51,500 --> 00:13:53,300
need to better determine the 
timing. 

255
00:13:53,800 --> 00:13:57,300
And then another big question is
did the great unconformity 

256
00:13:57,600 --> 00:14:00,300
develop in One Singular, 
massive? 

257
00:14:00,400 --> 00:14:02,800
Erosion event, for example, 
caused by something like 

258
00:14:02,800 --> 00:14:07,800
snowball Earth, or did it form 
at different times in different 

259
00:14:07,800 --> 00:14:11,700
places and have multiple causes?
For example, maybe there are 

260
00:14:11,700 --> 00:14:16,200
tectonic drivers in different 
locations, that ultimately led 

261
00:14:16,200 --> 00:14:20,500
to development of a feature that
looks the same everywhere, but 

262
00:14:20,500 --> 00:14:23,800
it actually has a Time 
integrated history that with 

263
00:14:23,800 --> 00:14:27,900
multiple erosion events, that 
Amalgamated to form, this 

264
00:14:28,000 --> 00:14:32,100
geologic Gap in the record. 
Go about dating that erosion 

265
00:14:32,100 --> 00:14:34,700
surface. 
Then you go and you can collect 

266
00:14:34,700 --> 00:14:37,300
samples from right below the 
Great unconformity. 

267
00:14:37,300 --> 00:14:41,100
And the minerals in these rocks,
immediately below the great 

268
00:14:41,100 --> 00:14:45,300
unconformity can retain the 
thermal history of that erosion 

269
00:14:45,300 --> 00:14:47,900
event that led to the 
development of that feature. 

270
00:14:48,300 --> 00:14:52,700
Even if the rocks that were 
eroded are now gone. 

271
00:14:52,800 --> 00:14:57,200
So, just below the great 
unconformity, erosion surface, 

272
00:14:57,800 --> 00:15:01,600
you pick out a mineral and you 
see when it's closer 

273
00:15:01,600 --> 00:15:05,600
temperature, drop pretty much 
close to what you'd expect on 

274
00:15:05,600 --> 00:15:08,200
the surface. 
I don't know, 20 degrees 10 

275
00:15:08,200 --> 00:15:13,300
degrees, something like that. 
And that age tells you when that

276
00:15:13,300 --> 00:15:15,900
service was last exposed. 
Is that the idea? 

277
00:15:16,100 --> 00:15:17,400
That's the idea. 
Yes. 

278
00:15:17,400 --> 00:15:20,100
Yeah, it can be more complicated
than that because there's all 

279
00:15:20,100 --> 00:15:22,600
kinds of stuff that happened 
since then, that you also have 

280
00:15:22,600 --> 00:15:26,500
to see through in order to get 
back at that erosion event. 

281
00:15:26,700 --> 00:15:30,200
But that is the basic idea. 
Wow, I can see how that could 

282
00:15:30,200 --> 00:15:31,900
be. 
Really powerful. 

283
00:15:32,500 --> 00:15:35,700
And so what have you been able 
to discover about the age of the

284
00:15:35,700 --> 00:15:37,600
great unconformity? 
Yeah. 

285
00:15:37,600 --> 00:15:40,100
So we've been working on the 
great unconformity in different 

286
00:15:40,100 --> 00:15:44,700
locations and it's clear that 
the timing of the last major 

287
00:15:44,700 --> 00:15:48,400
exclamation event that led to 
that development of the great 

288
00:15:48,400 --> 00:15:50,700
unconformity, erosion surface 
varies regionally. 

289
00:15:50,700 --> 00:15:54,200
So for example here in Pikes 
Peak Colorado we have data that 

290
00:15:54,200 --> 00:15:57,400
constrain the development of 
that surface to before 700 

291
00:15:57,400 --> 00:16:01,200
million years ago. 
Whereas in in the central 

292
00:16:01,200 --> 00:16:05,000
Canadian Shield, our data very 
clearly say that that feature 

293
00:16:05,000 --> 00:16:07,700
form there after 600 million 
years ago. 

294
00:16:07,900 --> 00:16:11,500
So it appears that the great 
unconformity can't be attributed

295
00:16:11,500 --> 00:16:14,600
to a singular sort of global 
event. 

296
00:16:14,900 --> 00:16:19,000
But rather that it formed 
heterogeneously a different 

297
00:16:19,000 --> 00:16:21,700
timing and possibly with 
different tectonic causes in 

298
00:16:21,700 --> 00:16:25,700
different places and so this 
makes it more difficult to tie. 

299
00:16:25,700 --> 00:16:29,800
It directly as a very specific 
and direct cause of the 

300
00:16:29,800 --> 00:16:31,700
Cambrian. 
First vacation of Life, although

301
00:16:31,700 --> 00:16:36,000
there still may be in direct 
links to environmental and 

302
00:16:36,000 --> 00:16:37,600
biologic change in this 
interval. 

303
00:16:38,300 --> 00:16:41,000
The great unconformity is very 
conspicuous. 

304
00:16:41,000 --> 00:16:44,800
As you mentioned in the Grand, 
Canyon has your work helped us 

305
00:16:44,800 --> 00:16:49,700
figure out the erosion history, 
there are p a PhD student 

306
00:16:49,700 --> 00:16:52,600
working with me required, you 
throwing helium data for 

307
00:16:52,600 --> 00:16:55,700
minerals and rocks, right below 
the great unconformity at 

308
00:16:55,900 --> 00:17:00,400
various locations within the 
modern Grand Canyon and Is 

309
00:17:00,400 --> 00:17:03,100
coupled that data with a variety
of geologic. 

310
00:17:03,100 --> 00:17:06,700
Constraints and a key Point here
is the history that she's 

311
00:17:06,700 --> 00:17:09,700
deciphering related to Great 
unconformity, development 

312
00:17:09,700 --> 00:17:12,800
occurred, hundreds of millions 
of years before the Grand Canyon

313
00:17:12,800 --> 00:17:15,599
itself was in size. 
So the Grand Canyon is in size 

314
00:17:15,599 --> 00:17:18,300
there now, and allows us to see 
the great unconformity and to go

315
00:17:18,300 --> 00:17:19,800
sample it. 
But the history that were 

316
00:17:19,800 --> 00:17:22,599
inferring doesn't have anything 
to do with the Grand Canyon 

317
00:17:22,599 --> 00:17:26,599
carving itself, but her work 
reveals that there was likely 

318
00:17:26,599 --> 00:17:30,200
paleo topography across that 
region in the eighth. 

319
00:17:30,400 --> 00:17:33,500
Our millionaire to 500 million 
year time frame, that was 

320
00:17:33,500 --> 00:17:37,800
developed due to faulting 
associated with assembly and 

321
00:17:37,800 --> 00:17:39,800
breakup of the rodinia 
supercontinent. 

322
00:17:39,800 --> 00:17:42,500
And so her data suggest for 
example that there was a high 

323
00:17:42,600 --> 00:17:45,400
Paleo High in. 
What is now the western part of 

324
00:17:45,400 --> 00:17:47,500
the Grand Canyon and opilio low 
in? 

325
00:17:47,500 --> 00:17:50,200
What is now eastern part of the 
Grand Canyon such that the 

326
00:17:50,200 --> 00:17:52,500
payload high in the western part
might have been shedding 

327
00:17:52,500 --> 00:17:55,700
sediments to the area to the 
East. 

328
00:17:55,700 --> 00:17:58,000
And so in these faults in the 
Grand, Canyon have been known 

329
00:17:58,000 --> 00:18:00,100
for a long time to have a 
history of repeated. 

330
00:18:00,300 --> 00:18:03,200
Reactivation. 
And so our interpretation is 

331
00:18:03,200 --> 00:18:07,400
that this faulting and paleo 
topographic Evolution occurred 

332
00:18:07,400 --> 00:18:10,400
during this multi-phase 
tectonic, activity during the 

333
00:18:10,400 --> 00:18:13,700
assembly and breakup of the 
rodinia supercontinent over 

334
00:18:13,700 --> 00:18:15,700
several hundred million year 
interval. 

335
00:18:15,900 --> 00:18:19,700
And so together this complicated
history, contributed to the 

336
00:18:19,700 --> 00:18:23,500
singular feature that we know as
the great unconformity in the 

337
00:18:23,500 --> 00:18:25,000
grand Canyon's. 
That's interesting. 

338
00:18:25,000 --> 00:18:29,000
So your thumb or chronology 
enables us to infer a possible 

339
00:18:29,000 --> 00:18:31,900
link between the To pull 
elevation changes and the 

340
00:18:31,908 --> 00:18:37,000
resulting erosion and the very 
large scale tectonic events 

341
00:18:37,000 --> 00:18:40,000
happening. 
At the time, from the Assembly 

342
00:18:40,000 --> 00:18:45,100
of rodinia supercontinent about 
a billion years ago to its 

343
00:18:45,100 --> 00:18:48,400
subsequent breakup about 750 
million years ago. 

344
00:18:49,300 --> 00:18:53,800
So let's talk about the 
long-term history of Continental

345
00:18:53,800 --> 00:18:58,200
cores or cretons. 
The conventional thinking has 

346
00:18:58,200 --> 00:19:00,200
been that these ancient blocks 
of content. 

347
00:19:00,300 --> 00:19:04,200
Continental lithosphere have 
just basically sat there since 

348
00:19:04,200 --> 00:19:09,200
they formed some of them over 2 
billion years ago, there's a 

349
00:19:09,208 --> 00:19:12,000
variety of data that clearly 
indicate that some of these 

350
00:19:12,000 --> 00:19:14,700
areas have undergone a more 
active history than we 

351
00:19:14,700 --> 00:19:18,500
previously realize we have been 
acquiring you throwing helium 

352
00:19:18,500 --> 00:19:23,000
data for samples across the 
interior of North America, that 

353
00:19:23,000 --> 00:19:26,900
show that some of these areas 
were buried by multiple km of 

354
00:19:26,908 --> 00:19:31,000
sedimentary rocks that were 
eroded and then, Read by 

355
00:19:31,000 --> 00:19:34,100
sedimentary rocks. 
And then those were eroded away 

356
00:19:34,100 --> 00:19:36,700
a second time. 
And so we can use our thermal 

357
00:19:36,700 --> 00:19:40,900
chronologic tool to decipher the
spatial extent, the thickness 

358
00:19:40,900 --> 00:19:42,300
and the erosion history of 
these. 

359
00:19:42,300 --> 00:19:45,500
Now eroded sedimentary units and
we're deciphering these 

360
00:19:45,500 --> 00:19:48,300
histories of barrel and erosion 
and places where most people 

361
00:19:48,300 --> 00:19:50,900
have assumed nothing has 
happened in that interval. 

362
00:19:51,100 --> 00:19:53,900
So this raises all kinds of 
interesting questions then like 

363
00:19:53,900 --> 00:19:58,500
why were these areas buried in a
row did multiple times when 

364
00:19:58,500 --> 00:20:00,700
we're in the middle of 
continents far from Plate 

365
00:20:00,800 --> 00:20:03,800
tectonic boundaries that 
traditionally people have looked

366
00:20:03,800 --> 00:20:08,200
to, to explain, large-scale, 
burial and erosion events in a 

367
00:20:08,208 --> 00:20:12,800
previous podcast, Carolina, 
Lithgow Bert saloni talked about

368
00:20:12,800 --> 00:20:17,400
Dynamic topography and how the 
elevated Topography of some 

369
00:20:17,400 --> 00:20:22,300
cretons met because at least in 
part by the force of an 

370
00:20:22,300 --> 00:20:26,800
upwelling mantle below. 
I understand that you've been 

371
00:20:26,800 --> 00:20:30,200
able to shed some light on that 
idea. 

372
00:20:30,300 --> 00:20:33,500
Pharmacology. 
Yeah this is exactly the kind of

373
00:20:33,500 --> 00:20:35,200
problem that we're trying to 
tackle. 

374
00:20:35,200 --> 00:20:38,500
So both with some of our work 
across North American Interior 

375
00:20:38,500 --> 00:20:43,400
as well as in southern Africa. 
Because if you think of how 

376
00:20:43,400 --> 00:20:46,900
elevations vary in different 
locations, like the East Coast, 

377
00:20:46,900 --> 00:20:48,900
like where you are Oliver 
sitting at sea level. 

378
00:20:48,900 --> 00:20:51,900
And me here, Mile High here in 
Boulder Colorado. 

379
00:20:52,400 --> 00:20:56,000
You can either look to 
differences in the thickness and

380
00:20:56,000 --> 00:20:59,100
the buoyancy structure of the 
crust and the lithosphere. 

381
00:20:59,100 --> 00:21:02,000
So this is like the the buoyant 
part of the earth or you can 

382
00:21:02,000 --> 00:21:05,700
look to deeper mental processes 
that might be driving 

383
00:21:05,800 --> 00:21:09,100
differences in the elevation. 
And in the same way changes in 

384
00:21:09,100 --> 00:21:12,500
the lithosphere buoyancy 
structure or changes and mantle 

385
00:21:12,500 --> 00:21:16,100
flow patterns, which some people
call Dynamic topography that can

386
00:21:16,100 --> 00:21:18,400
cause elevation change over 
time. 

387
00:21:18,600 --> 00:21:21,400
And so if you're sitting near 
the plate margin, like if you're

388
00:21:21,400 --> 00:21:25,300
in the Himalayas or in the 
Andes, it's easy to say, okay, 

389
00:21:25,300 --> 00:21:28,300
we'll plate tectonic processes 
that are a consequence of plate,

390
00:21:28,300 --> 00:21:31,500
sliding back and forth, and 
Sighing, the crust are 

391
00:21:31,500 --> 00:21:33,600
responsible for the elevation 
change, but if you're in the 

392
00:21:33,600 --> 00:21:36,500
middle of continents, you don't 
have that as a mechanism. 

393
00:21:36,800 --> 00:21:40,600
And so a good place to go, try 
to decipher the effects of 

394
00:21:40,600 --> 00:21:43,900
dynamic, topography are in some 
of these Continental cores, 

395
00:21:44,000 --> 00:21:46,200
where your shielded from the 
plate boundaries. 

396
00:21:46,500 --> 00:21:49,900
So you don't have significant 
plate tectonic. 

397
00:21:50,000 --> 00:21:54,100
Effects, over printing, your 
signal and southern Africa is 

398
00:21:54,100 --> 00:21:58,000
particularly interesting because
it's one of the most widely 

399
00:21:58,000 --> 00:22:01,500
cited examples of elevated. 
Dynamic topography on the 

400
00:22:01,508 --> 00:22:03,900
continent. 
So southern Africa is a plateau 

401
00:22:04,200 --> 00:22:07,100
and unlike all of the other 
major plateaus on earth, like 

402
00:22:07,100 --> 00:22:09,900
the Colorado Plateau or the 
Tibetan Plateau, those other 

403
00:22:09,900 --> 00:22:13,500
plateaus were in some kind of a 
contractional plate boundary 

404
00:22:13,500 --> 00:22:15,300
setting. 
So a setting where two plates 

405
00:22:15,300 --> 00:22:18,100
are moving together. 
When they underwent elevation 

406
00:22:18,100 --> 00:22:20,900
gain, the southern African 
Plateau was completely 

407
00:22:20,900 --> 00:22:24,300
surrounded by plate boundaries, 
that were pulling apart when it 

408
00:22:24,300 --> 00:22:27,000
became elevated. 
And so for this reason, people 

409
00:22:27,000 --> 00:22:30,800
have pointed towards deeper 
mantel processes as Possibly 

410
00:22:30,800 --> 00:22:33,600
being responsible for elevation 
gain. 

411
00:22:33,800 --> 00:22:38,200
A dynamicists like Carolina have
imaged deep structures in the 

412
00:22:38,200 --> 00:22:40,000
mantle. 
That might be responsible for 

413
00:22:40,000 --> 00:22:41,800
that. 
So, how did you go about 

414
00:22:41,800 --> 00:22:44,800
disentangling of the causes of 
uplift and southern Africa. 

415
00:22:45,300 --> 00:22:49,500
So our projects was aimed at 
deciphering the erosion history 

416
00:22:49,500 --> 00:22:52,100
across the interior of the 
Southern African plateau. 

417
00:22:52,200 --> 00:22:54,700
And one of the things we 
specifically did was work on 

418
00:22:55,000 --> 00:22:56,600
what are called kimberlite 
pipes. 

419
00:22:56,600 --> 00:23:00,000
So these things are small 
volume, volatile, rich. 

420
00:23:00,200 --> 00:23:02,800
Magma is like volcanoes but they
contain most of the world's 

421
00:23:02,800 --> 00:23:05,200
diamonds and they come up 
through these ancient cores of 

422
00:23:05,200 --> 00:23:07,200
continents. 
And these things come blasting 

423
00:23:07,200 --> 00:23:09,900
up from deep in the mantle and 
they sample the lithospheric 

424
00:23:09,900 --> 00:23:12,500
mantle and then pieces of the 
crust and then any of the 

425
00:23:12,500 --> 00:23:14,200
sedimentary cover at the 
surface. 

426
00:23:14,600 --> 00:23:17,800
So what we did was acquire 
thermal chronology data on 

427
00:23:17,800 --> 00:23:21,100
samples collected across 
southern Africa, to decipher the

428
00:23:21,100 --> 00:23:24,700
timing, the history and patterns
of erosion across two different 

429
00:23:24,700 --> 00:23:28,400
regions there. 
So, one of these regions had a 

430
00:23:28,500 --> 00:23:30,900
very strong record of 
Lithospheric. 

431
00:23:30,900 --> 00:23:34,600
Mantle alteration as recorded by
kimberlite pipes that had 

432
00:23:34,600 --> 00:23:37,400
erupted through that area. 
And then the other area had 

433
00:23:37,400 --> 00:23:40,500
relatively little modification 
of the lithospheric mantle 

434
00:23:40,500 --> 00:23:43,900
structure. 
And so what we found is in the 

435
00:23:43,900 --> 00:23:47,000
area with substantial 
lithospheric modification, we 

436
00:23:47,100 --> 00:23:52,200
found a phase of pronounced 
erosion that coincided with win 

437
00:23:52,300 --> 00:23:55,700
that lithospheric modification 
occurred, telling us that 

438
00:23:55,700 --> 00:23:58,900
lithospheric modification 
process likely was responsible 

439
00:23:58,900 --> 00:24:02,600
for the Engane and therefore the
erosion history that we see in 

440
00:24:02,600 --> 00:24:06,900
that area, in contrast in the 
region that underwent less 

441
00:24:07,000 --> 00:24:09,900
lithospheric modification. 
We see a much more protracted 

442
00:24:09,900 --> 00:24:13,200
erosion history. 
We see a phase of scarp Retreat 

443
00:24:13,200 --> 00:24:17,700
over several tens of millions of
years across the plateau and 

444
00:24:17,700 --> 00:24:21,200
because this area underwent less
lithospheric modification. 

445
00:24:21,200 --> 00:24:25,300
This points towards deeper 
mental processes such as Dynamic

446
00:24:25,300 --> 00:24:28,600
topography effects, that 
probably contributed to the 

447
00:24:28,600 --> 00:24:31,700
elevation gain there. 
So together, these results 

448
00:24:31,800 --> 00:24:36,800
indicate that both lithospheric 
and deeper Dynamic processes, 

449
00:24:36,800 --> 00:24:41,200
likely caused the rise of the 
Southern African Plateau with 

450
00:24:41,200 --> 00:24:44,900
the relative influences of those
two processes, varying spatially

451
00:24:44,900 --> 00:24:46,600
across the plateau. 
Wow. 

452
00:24:46,600 --> 00:24:50,300
So the bottom line is that, at 
least under the southern African

453
00:24:50,300 --> 00:24:55,100
Plateau, we really are seeing 
the effects of dynamic 

454
00:24:55,100 --> 00:24:58,100
topography. 
Yes, Dynamic Topography is real,

455
00:24:58,100 --> 00:25:02,300
but is not the only part of the 
story related to the rise of the

456
00:25:02,300 --> 00:25:05,500
Southern African Plateau. 
Most of the work you've talked 

457
00:25:05,500 --> 00:25:10,400
about so far has been based on 
analyzing minerals like Zircon 

458
00:25:10,400 --> 00:25:14,300
or appetite. 
But what about rocks that don't 

459
00:25:14,300 --> 00:25:18,900
contain these minerals such as 
shells and limestone's Shields 

460
00:25:18,900 --> 00:25:22,100
and limestone's form, thick 
sections and sedimentary basins.

461
00:25:22,100 --> 00:25:23,900
But it turns out you know, 
shales and limestone's. 

462
00:25:23,900 --> 00:25:26,500
They don't have any minerals 
that are easily dated or in the 

463
00:25:26,500 --> 00:25:29,500
past have been easily dated with
firmer chronology and so we 

464
00:25:29,500 --> 00:25:33,400
attempted to Date conodonts in 
shells and limestone's. 

465
00:25:33,400 --> 00:25:37,800
So these are micro fossils. 
These are Critters that lived 

466
00:25:37,800 --> 00:25:41,500
for several hundred million 
years in the Paleozoic and early

467
00:25:41,500 --> 00:25:43,800
Mesozoic. 
So for thing, like 500 million 

468
00:25:43,800 --> 00:25:47,200
years ago, until maybe 300 
million years ago and they're 

469
00:25:47,200 --> 00:25:51,300
very common these conodonts, 
they're actually bio appetite in

470
00:25:51,300 --> 00:25:53,300
many rocks, we date, Crystal, 
and appetite. 

471
00:25:53,300 --> 00:25:56,600
But these are actually appetite.
That is biologically formed, 

472
00:25:56,600 --> 00:25:58,600
like, your teeth are bio 
appetite. 

473
00:25:58,800 --> 00:26:01,500
We tried to date some of these 
materials to develop as a 

474
00:26:01,508 --> 00:26:04,900
thermal chronometer and it 
wasn't as easy as other 

475
00:26:04,900 --> 00:26:07,000
minerals. 
One of the challenges is that. 

476
00:26:07,100 --> 00:26:10,100
These conodonts, they don't 
start off with lots of uranium, 

477
00:26:10,100 --> 00:26:11,700
and Thorium in them. 
Like, you don't have lots of 

478
00:26:11,700 --> 00:26:13,500
uranium and Thorium in your 
teeth, these Critters did not 

479
00:26:13,500 --> 00:26:14,500
die. 
They did not have a lot of 

480
00:26:14,508 --> 00:26:15,900
uranium, thorium and their 
bodies. 

481
00:26:16,000 --> 00:26:17,700
So what happens is these 
Critters, die. 

482
00:26:17,700 --> 00:26:20,900
And these conodonts are 
deposited and they acquire, 

483
00:26:21,100 --> 00:26:23,500
uranium and thorium as they get 
buried. 

484
00:26:23,700 --> 00:26:26,300
And what this means is that, the
uranium and thorium is more 

485
00:26:26,300 --> 00:26:29,300
mobile and for a junior 
chronometer thermal chronometer,

486
00:26:29,300 --> 00:26:32,200
it's very bad you Want your 
parent isotope to be mobile and 

487
00:26:32,200 --> 00:26:34,800
be lost from your Crystal. 
There are different content 

488
00:26:34,800 --> 00:26:37,000
components. 
And so I have not totally given 

489
00:26:37,000 --> 00:26:39,500
up on this idea, because if you 
could use this to constrain 

490
00:26:39,500 --> 00:26:41,500
thermal history, so it would be 
extremely powerful. 

491
00:26:42,100 --> 00:26:45,400
And as I mentioned in the 
introduction, you're even 

492
00:26:45,400 --> 00:26:49,300
working on lunar rocks. 
What can thermal chronology 

493
00:26:49,300 --> 00:26:54,100
reveal about those on the moon? 
The firm will histories are 

494
00:26:54,200 --> 00:26:58,900
induced by meteorite impact 
processes early in the solar 

495
00:26:58,900 --> 00:27:01,800
system, we know. 
That there were lots of impacts 

496
00:27:01,800 --> 00:27:05,100
that this caused melting of the 
surface and planetary, 

497
00:27:05,100 --> 00:27:08,800
resurfacing and at some point in
time that impact flux decline to

498
00:27:08,800 --> 00:27:12,700
modern-day background levels. 
And so a big question is when 

499
00:27:12,700 --> 00:27:15,900
and how did this flux Decline? 
And so in order to figure this 

500
00:27:15,900 --> 00:27:19,900
out this requires dating, the 
history of meteorite impacts on 

501
00:27:19,900 --> 00:27:22,600
the moon. 
So using uranium from Helium, we

502
00:27:22,600 --> 00:27:26,000
can begin to decipher parts of 
that history, to constrain the 

503
00:27:26,000 --> 00:27:29,200
tiny and the thermal effects, 
the magnitude of these impact 

504
00:27:29,200 --> 00:27:32,000
events, right? 
Have a new NASA project, where 

505
00:27:32,000 --> 00:27:35,200
we're doing additional work, on 
lunar materials, to try to 

506
00:27:35,200 --> 00:27:37,900
constrain that history, and it's
really cool to be working on 

507
00:27:37,900 --> 00:27:40,600
samples, that came back from the
Apollo Mission. 

508
00:27:41,200 --> 00:27:44,500
But when you have an impact 
event, you have a momentary, 

509
00:27:44,700 --> 00:27:49,100
huge heating. 
Do you then also have a slow 

510
00:27:49,100 --> 00:27:52,800
cooling history that you can 
track on the moon? 

511
00:27:52,800 --> 00:27:56,000
We have these short, as you say,
a very intense Heating and 

512
00:27:56,000 --> 00:27:58,500
Cooling events. 
So, whatever kinetic models, we 

513
00:27:58,500 --> 00:27:59,900
develop have to be able to 
handle. 

514
00:28:00,100 --> 00:28:03,600
Short-term events, but then on 
the lunar surface also, it's 

515
00:28:03,600 --> 00:28:06,200
pretty hot. 
So, we also have to consider the

516
00:28:06,200 --> 00:28:08,900
effects of some of these samples
sitting at the surface of the 

517
00:28:08,908 --> 00:28:12,500
Moon, for a long time, and being
relatively warm and deconvolve 

518
00:28:12,500 --> 00:28:17,800
that from the effects of these 
short extreme, heat pulses, and 

519
00:28:17,900 --> 00:28:22,000
have you been able to get some 
results on the bombardment 

520
00:28:22,000 --> 00:28:26,300
history of the lunar? 
Surface data, allow us to detect

521
00:28:26,300 --> 00:28:31,700
a 3.95 billion-year-old impact 
event. 110 million year impact 

522
00:28:31,700 --> 00:28:34,800
event, and they allow us to 
limit the temperature of any 

523
00:28:34,800 --> 00:28:37,400
impact event. 
That would have occurred between

524
00:28:37,400 --> 00:28:40,100
those two impacts that I just 
described. 

525
00:28:40,100 --> 00:28:43,000
And so that gives us an insight 
into the impact history in the 

526
00:28:43,000 --> 00:28:45,600
thermal history at one spot on 
the lunar surface. 

527
00:28:46,000 --> 00:28:48,400
But then by working on other 
samples with different 

528
00:28:48,400 --> 00:28:51,200
histories, the idea is that by 
integrating those that will be 

529
00:28:51,200 --> 00:28:54,900
able to gain a more 
comprehensive picture of the 

530
00:28:54,900 --> 00:28:59,100
larger lunar history. 
For my last question, I want to 

531
00:28:59,100 --> 00:29:03,800
ask you about the capabilities, 
you dream about having in your 

532
00:29:03,800 --> 00:29:07,100
lab especially if there were no 
funding constraints. 

533
00:29:07,500 --> 00:29:10,100
What I would really want. 
If I had unlimited funding would

534
00:29:10,100 --> 00:29:12,500
be to invest in human 
infrastructure. 

535
00:29:12,600 --> 00:29:15,100
Just talking with you today. 
You can see we deal with the 

536
00:29:15,100 --> 00:29:17,300
normal spatial scales and 
temporal scales. 

537
00:29:17,300 --> 00:29:21,100
So we worry about nanoscale like
how does diffusion occur in our 

538
00:29:21,100 --> 00:29:23,000
structure? 
And there's a variety of light 

539
00:29:23,000 --> 00:29:26,300
material characterization tools 
and all kinds of new tools that 

540
00:29:26,300 --> 00:29:28,900
people are Developing in other 
fields, that might help us 

541
00:29:28,900 --> 00:29:31,300
better understand diffusion at 
that nanoscale. 

542
00:29:31,500 --> 00:29:34,600
But at the same time we're 
trying to extrapolate that to 

543
00:29:34,600 --> 00:29:37,500
uplift at the Continental scale 
or characterizing short 

544
00:29:37,500 --> 00:29:40,700
experiments in our lab over S 
and H and we're trying to 

545
00:29:40,700 --> 00:29:44,300
extrapolate that to figure out 
histories back of the Moon back 

546
00:29:44,300 --> 00:29:47,500
to 4.5 billion years ago to 
Grapple with this, you really 

547
00:29:47,500 --> 00:29:50,500
need people who think about that
nanoscale. 

548
00:29:50,500 --> 00:29:53,300
We need to have improved 
statistics and uncertainty 

549
00:29:53,300 --> 00:29:56,100
characterization and people can 
do the modeling and the coding 

550
00:29:56,100 --> 00:29:59,200
and then people who about those 
big problems and so thinking 

551
00:29:59,200 --> 00:30:02,700
about how to better use the 
tools we have and to get people 

552
00:30:02,700 --> 00:30:04,700
working creatively on all 
different aspects of the 

553
00:30:04,700 --> 00:30:07,000
problem. 
Like if I had unlimited money, I

554
00:30:07,000 --> 00:30:10,500
would put it into people. 
Becky, flowers. 

555
00:30:10,600 --> 00:30:12,700
Thank you very much. 
Thank you Oliver. 

556
00:30:12,700 --> 00:30:15,900
This is great. 
I really enjoyed it. for more 

557
00:30:15,900 --> 00:30:20,100
about geology b, as well as 
pictures and illustrations, that

558
00:30:20,100 --> 00:30:24,400
support this podcast, you can go
to geology B.com