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In your planet's Carboniferous era, the atmosphere had a substantially higher oxygen content.
This permitted very large insects to evolve. Insects have no lungs, relying instead on simple diffusion through a network of tubes.
Since they have a short life cycle, which can be artificially shortened,
and it is easy to create an environment with superelevated oxygen levels, selective breeding would soon produce a population of very large insects.
Apart from being a public curiosity, and interesting for scientific research, insects are efficient at converting low grade vegetable matter into protein, and could be a useful food source.
No direct gene modification is involved, and if the insects escape they'll suffocate.
Buggalo
http://insteading.w...2014/04/buggalo.jpg
[Voice, Jul 11 2016]
Oxygen increased from 21% to 31%
http://www.wired.co...dragonflies-oxygen/
resulted in a 15% size increase. [FlyingToaster, Jul 11 2016]
We have been here before...
Dome_20of_20Giant_20Insects
[MaxwellBuchanan, Jul 11 2016]
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I'm not sure if the higher oxygen content is the
only, or even the main explanation for the
embiggenment of insects. |
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It was 35%, as opposed to today's 21% - a roughly
1.5-fold difference. You might expect that to
allow for insects at most 1.5-times larger
(linearly), given the same anatomy and assuming
that the limiting factor is the diffusion of oxygen. |
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I think many factors allowed insects to get so big,
including temperature (vitally important for a
cold-blooded animal), lack of many other apex
predators, and so on. |
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In fact, today, there are some fairly huge insects in
the tropics, but very few large ones in temperate
climates, despite the oxygen content being the
same. |
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//if the insects escape they'll suffocate.// |
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Can't have that... itty bitty rebreathers and O2 tanks would seem to be in order. |
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Sir Buz-a-Lot, at the entomologist convention: "I like big bugs and I cannot lie"! |
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It seems to be the opposite of my Resurrection of the Dead
idea, where people are developed to become smaller. |
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//The earth also revolved faster back then reducing gravity// That would explain why equatorial insects are much larger than polar ones. |
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//The earth also revolved faster back then
reducing gravity which would enable extra size for
both landborne and flying insects.// |
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True, yet also very wrong. The day length in the
carboniferous was about 22 hours. |
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Effective G (subtracting centripugal from
gravitational forces) at the equator today is
9.77m/s2, as opposed to 9.80 at the poles. With a
roughly 10% faster rotation in the carboniferous,
the centrifugal force at the poles would be about
20% greater than it is today, giving an effective G
of about 9.76m/s2. |
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In other words, even at the equator the effective
G has increased by only about 0.1% since the
carboniferous. |
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Hey, that 15% bigger dragonfly was only in the first
year, with no selective breeding. |
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yup: went from a 3œ" wingspan to 4, without any genetic mods, just by increasing the O2 level. I wonder if increasing the pressure would have the same effect (in two ways : increasing O2 availability and making it easier to fly). It'd be a more difficult experiment, requiring a pressure container. |
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A quick search suggests that the main contender for the shrinking of insects is the evolution of birds.
Now, as I'm sure we all know, birds are evolved from dinosaurs. |
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I like the idea of megafauna something like a pterosaur feasting on an abundance of enormo-flies, which evolved away from this selection pressure by reducing in size. This of course lead to a miniaturisation arms race to the glorious sparrows and robins we have today. |
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So I read this, and got all interested in the carboniferous
period. After all, we have that to thank for the rather
generous amounts of coal allocated to Britain to allow for
the industrial revolution, employment of the Welsh and
the rather pretty limestone we use to decorate the
southern shore of Britain*. Now, I had a think about the
massive insects too, and you don't really need big oxygen
concentrations. Insect physiology is cleverer than the
Scientists who came up with all that passive diffusion
nonsense. There's lots of coordinated volume changes and
valving going on, and there was then. |
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Then I got interested in where all this high oxygen stuff
came from. Most references seem to point to this one
PNAS paper <link>. Now, nothing wrong with PNAS, solid
journal, but you can't believe everything in it. I don't
believe some of the stuff I have published in it for
example**. Worse, it's got 2 figures, a dodgy diagram and
a Excel95-on-default graph. There is a bit of circular
reasoning going on regarding oxygen and animal size and
that old beauty of 'modelling' for the relationship
between Iron, Sulfur, Carbon, Calcium, Carbon Oxygen
and water. |
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We know that lots of carbon was laid down into coal.
Trees of the period were almost all bark (8-20:1 Vs 1:4
for modern) which is good insect defense, from massive
insects and essentially doesn't rot. It's also big on carbon.
At the same time Carbon is also being laid down as
limestone. So a big movement to form solid carbon.
Liberating O2, but there can't have been enough CO2 to
account for an additional 10% O2, or even 5 I'm calling
made up crap on that. |
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Anyhow, a 5-10% increase in the O2 portion of the
atmosphere wouldn't go unnoticed... it's not going to
replace nitrogen, its additional. So the total atmospheric
mass must increase, a lot. So surface air pressure
increases. I think a good explanation for massive insects,
particularly flying ones is here. Increased pressure and
oxygen concentration would certainly increase max
growth rate, which will help max size and performance of
vascular/muscle system. There will also be a slight
buoyancy effect... I reckon Everest wouldn't have been a
difficult climb, if it didn't have the cheek to not exist. |
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Anyhow, having messed around with a raw ice core data
for the last couple of hours I can't find any sensible
measurements of total O2, or N2 or Argon really. They're
very good on O18 as a ratio, obsessed with CO2, but total
O2 and N2? very hard to find. |
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*Stick with the dull grey stuff, white's a bugger to clean. |
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**Don't base anything meaningful on Supplementary fig 4. |
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//difficult experiment, requiring a pressure container// |
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Do it in one of those nuts South African mines, 3.4 km down
you're at 1.4 atmospheres. |
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//Anyhow, a 5-10% increase in the O2 portion of the atmosphere wouldn't go unnoticed... it's not going to replace nitrogen, its additional. So the total atmospheric mass must increase, a lot. So surface air pressure increases.// |
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Um... I was thinking the opposite. The O2 is created by photosynthesis:
CO2 -> O2 + [fixed carbon]
So an overall decrease in atmospheric mass. |
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(Obviously other factors may apply; CO2 was presumably escaping from the Earth's interior - as it still does.) |
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How long before the CO2 alarm bell goes off? |
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//The O2 is created by photosynthesis:
CO2 -> O2 + [fixed carbon]// |
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From what I read, no one suggests above around 4% CO2
for
anywhere within millions of years before the supposed O2
increase. Where the O2 comes from... who knows? But
there's sulfur and iron oxides to consider. Then there's all
the H2 locked up in the hydrocarbon deposits,
presumably leaving the O to its own devices. To be fair,
paleoclimatology seems to be largely
back of the envelope stuff. |
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Maybe there was a great deal of lightning at that
time...electrolysis? |
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//Maybe there was a great deal of lightning at that
time...electrolysis?// |
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In a world with just two massive connected continents,
high pressure high percentage oxygen (and less water
vapor) and infinite trees. I would fear lightning. You'd
expect frequent forest fires. So a long slow drawdown of
CO2 by the trees punctuated with spikes from continent
scale fires which would end up in limestone and new
plants. |
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If humanity does end up destroying its own environment,
we can offer up a strong defense. "The trees did it first"
as defense. "I offer up to the high-galactic justice council
that humanity was merely the latest in a long line, the
trees got so good at consuming CO2 that they polluted
the atmosphere with dangerous levels of oxygen. Their
only predators, the giant insects, were fended off with
ostentatious and unnecessary amounts of non-
biodegradable lignin-rich bark. The atmosphere bulged
with waste O2, the continents littered with intractable
carbohydrates, with no proper risk assessments or
planning regulations huge fires were inevitable. I forward
the motion that the brave British bravely employed the
Welsh to extract the stolen carbon, contriving elegant
machines to selflessly return the same to the atmosphere
for the common good". |
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// the brave British bravely employed the Welsh to extract the stolen carbon // |
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Sp. "The brave and noble English bamboozled the ignorant mouth-breathing taffs into digging up loads of black rock because they were told you can make diamonds from it*" |
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*Bizarrely, this is true. It just isn't very easy. Hitting a lump of coal with a hammer** does not produce the temperatures and pressures needed to persuade carbon atoms to re-arrange into a regular tetrahedral crystal. |
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**No, not even a really big*** hammer. |
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***No, not even Grandpa Dai's sledgehammer that you can only just lift. You can't make diamonds by hitting coal with a hammer. No, you can't have just one more try. Come in out of the rain now, it's time for you to have your mug of lovely boiled grass broth. Yes, you can have extra mud in it. No, you can't learn the secret of the glowing orange hot thing, that's only for the High Druids. |
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