Translator: Amanda Chu Reviewer: Rhonda Jacobs
I was just looking out the window,
(Laughter)
and our atmosphere on edge,
it's this thin, blue line,
and that's all that separates us
from the vacuum of space.
Selfieee! selfie!
(Laughter)
I couldn't help but wonder,
How did our atmosphere get here?
How did it evolve through geologic time?
And here is what is known.
Now, one of the things that's known
is I'm using the latest NASA graphics here.
(Laughter)
These graphics are so good
they make things look like they're handwritten.
And this is a plot of geologic time
from then until now.
And here's Earth,
and this is pressure, atmospheric pressure,
and Earth has one atmosphere.
By definition, it's kind of like measuring the length of a foot
based on whoever happens to be king for the moment, right?
So Earth by definition has one atmosphere;
but Venus, our nearest neighbor, hundred atmospheres pressure;
and Mars, 1/100 of an atmosphere pressure.
So we know in the here, in the now,
for rocky, Earth-like planets,
you can have atmospheric pressures
much greater than what we have
and much less than what we have,
and for the case of Mars,
we know there are mechanisms to lose atmospheric pressure.
What about back then?
There's not a whole lot in the geologic record
dealing with atmosphere.
Geologic record preserves all kinds of other fascinating things
about Earth and its evolution,
but atmosphere seems to be missing.
So what is done is they assume
that Earth started off, day one, with a Venus-like atmosphere,
and this is actually a decent assumption
based on the fact that we don't know what the atmosphere really was.
And what about in between then and now?
And again, there's almost nothing in the geologic record, scant evidence,
for our atmospheric pressure,
so you could draw almost any line you wanted.
Now, there is evidence, proxy evidence,
in the geologic record for atmospheric composition,
but pressure is different from the composition;
and if you're interested in the pressure, there's not much evidence.
So what is done -
you use sound principles of chemistry and principles of geophysics,
and you come up with the following curve:
You find that with a Venus-like atmosphere,
the pressure will rapidly decrease over geologic time,
you know, maybe a hundred million years,
and then it levels off,
and by the time there were wide-scale, large creatures walking around,
it's taken that Earth's total atmospheric pressure
is essentially unchanged from today.
So, what about other clues to the past?
Is there something else that you might be able to use as a proxy,
not to actually tell you what the number was,
but something that you could infer
what our atmosphere might have done as a function of time?
And this took me to prehistoric creatures
that might infer something about our prehistoric atmosphere.
And the creatures are pterosaurs - giant pterosaurs.
These were humongous.
Some of them had wingspans half that of a 737 -
giant flying creatures.
And there's many varieties.
These are Pteranodons,
drawn to scale using exact NASA measurements.
(Laughter)
And you can see the Pteranodons were human size,
but look at the Quetzalcoatlus:
This is a large creature -
50-foot wingspans, 250 up to 300 pounds.
These were creatures, flying creatures, larger than human beings.
So what is known about these?
Well, in the literature, there's all kinds of scientific papers published,
specifically about pterosaurs:
their biomechanics, their metabolics, their aerodynamic parameters,
how they could possibly fly or maybe their flightlessness.
Then, if you look in the here now, we've got birds.
And birds are fascinating to study,
and there's literally dozens of books written about bird flight,
and then hundreds and hundreds of papers,
scientific papers, engineering papers,
talking about bird flight,
and a common thread in all this literature
is that these huge pterosaurs were too big to fly.
Too big to fly!
[Pterosaurs - too big to fly?]
And what is assumed is that these were opportunistic flyers,
that they were soaring creatures;
they would sit on top of a cliff,
and they'd wait till thermals were to develop,
they'd wait for winds to blow, and then they could jump off and fly.
And this is a perfectly sound assumption
if you can't figure out how they could have flown
in the first place.
[Power - Body Mass]
Now, this cartoon
shows the crux of why they're too big to fly.
You have power plotted against body mass,
and there's two important curves, two important curves.
One is the power for flight,
and this is taken from the literature
from these things called "great flight diagrams,"
where people have measured powers and stall speeds and all these things
from the tiniest of bird to the largest of bird,
and then when you add human-made machines,
airplanes and things,
these curves are extensible all the way up to 747 jumbo jets,
so we know what it takes from the power to fly.
And then there's a metabolic power,
and these come from mouse to elephant curves.
These are metabolic power curves for warm-blooded vertebrates,
from the tiniest of shrew to the largest of elephant,
and given the mass of a creature,
we know within a range
what its metabolic power could be.
And notice there's a crossover point,
beyond which a creature has insufficient metabolic power
in order to fly.
Now, this may be wrong,
but my next slide is going to be filled with numbers,
actual numbers from the literature -
and for this venue, you know,
we're all relaxed here on a Saturday afternoon,
and showing a slide with all of these numbers that may be wrong -
but here's a tip:
don't think about the numbers, just feel the numbers,
just let the numbers talk to you,
and maybe it'll be like one of those neuro things
that we saw here earlier.
You just feel the numbers.
So, and it'll only take 30 seconds.
Ready?
Here goes.
Here's the power for flight in watts versus body mass in kilograms,
going up to 20 kilograms.
There's two important curves:
There's a power for flight
taken from the great flight diagrams in the literature.
Here is the metabolic power taken from the mouse to elephant curves.
There is the crossover point at 13 kilograms.
And you take all our known flyers.
They land here:
cormorants, bald eagles, vultures, albatross, condors, kori bustards -
you've got to say that word carefully and got to enunciate that one.
(Laughter)
And notice -
Oh, 36 seconds, 36 seconds. That's not too bad.
Notice we have no creatures alive today
that can fly beyond the crossover point.
Now, I'm thinking maybe this had something to do with Darwin,
but who knows.
Now, I'm going to show one more slide, one more slide, like this,
but it's extended into the mass range that covers the Quetzalcoatlus.
So, here we go.
We've seen this:
power in watts, mass in kilograms, going upwards to 120 kilograms.
There's the power-for-flight line, there's the metabolic power line,
and here's the crossover point at the kori bustard,
at 13 kilograms.
You take Pteranodons all the way up to Quetzalcoatlus,
and they go here.
So, these large flying creatures
not only lack the power to fly by a little bit,
they lack the power to fly by a whole lot.
So, we have these creatures that in every possible way,
they look like they should be able to fly,
but we as human beings
aren't smart enough to figure out how they could fly,
so I thought let's make some assumptions.
And my first assumption is that they were true flyers,
they had the ability for true flight,
that even though they existed before Darwin,
the same principles of Darwin applied back then as they do now.
I'm going to assume
they have similar metabolics to today's warm-blooded creatures.
We have no information on what their cell physiology was like.
You know, maybe they ran off off kryptonite,
(Laughter)
but I'm going to assume
that their cell physiology is the same as warm-blooded creatures of today,
and then I'm going to assume
that we understand something about aerodynamics.
Of these three assumptions,
the understanding of aerodynamics
is probably the weakest of all of these assumptions,
particularly my understanding of aerodynamics,
but entertain me for right now.
Let's see where we could go with this.
So here's my artistic ability to draw a pterodactyl,
and if you look at the power-for-flight equations,
there is a pressure term -
as the pressure goes up,
the power for flight goes down.
So what happens
maybe if our early atmosphere at the time of the dinosaurs
had more pressure than what we have today?
Let's see how much it would have to be.
So here's our plot.
We've seen this before:
power versus mass, the power for flight, metabolic power, kori bustard,
crossover point, 13 kilograms,
Pteranodons all the way up to Quetzalcoatli -
I'm thinking it's Quetzalcoatli,
in plural form.
And the power for flight, that black line,
it's assumed it's always done at one atmosphere
because that's what we have here on Earth right now.
But if you use the equations
and you just start to crank up the atmospheric pressure,
you find that that power-for-flight line will hinge down to lower powers,
and so I'm going to do this mathematically
until that line hinges down to the crossover point
in the mass range of the Quetzalcoatlus.
And here's what the result is.
So the blue line, hinge down,
changing the crossover point from 13 kilograms at the kori bustard
all the way up to the mass range of the Quetzalcoatlus,
at 3.2 atmospheres pressure -
3.2.
Now, if you look at these equations,
there's always air bands within all the parameters and such,
and if you stack and dice all these things up
and redo for a range,
you find that the blue line, the power-for-flight line
would cross at the mass range of Quetzalcoatlus
for somewhere around two and a half to four atmospheres pressure.
Let's relook at our evolution plot for Earth's atmosphere.
And here we are, in the here and now,
with Earth at one, Venus at 100, Mars at 1/100,
and here's what's assumed
taken in the literature for the evolution of our atmosphere.
And perhaps using the aerodynamics of pterosaurs,
you could postulate that during the time of the dinosaurs,
you might have three times more atmosphere
than what we currently have.
And of course with this inference,
you can't assume or figure out anything that happened
before the age of these large flying creatures that's unknown.
So, a proxy for the past,
and a proxy - if you want to make a measurement,
but for some reason the data is obscured or the conditions are such
so that you cannot make that measurement directly,
you might be able to infer something else
as a proxy to hypothesize a range
for the parameter that you really want.
So, using proxy measurements for the past
with pterosaurs and aerodynamics,
you could infer
that perhaps Earth's atmosphere in the time of the dinosaurs
was three times greater pressure than what we find today.
Now, the follow-on question is,
What happened to this extra atmosphere since then and now?
And that will be the subject for another talk.
(Laughter)
Thank you.
(Applause)