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Please hold on to flag as off-topic.

Few days ago I received a question - how big an egg can possibly big? Can it be as big as 1 meter, as a human? (Imagining that there could be really huge animals which would lay these eggs)

My thoughts are that an egg should have an upper limit and basically you can find out the biggest possible egg for Earth. By big I assume the biggest volume.

I started to think this way - the thing inside the egg should breath, therefore the egg should allow CO2 and O2 to go in and out. The thing inside the egg consumes constant amount of O2 which is related to the volume of the egg. On the other hand the surface of the egg is related to the amount of air the baby can breath. But with the increase of the size of the egg - the volume is growing much faster then the surface. So at some point of time the amount of air going inside of the egg would not be enough.

I think that I am on the right track, but can not finish it to receive the answer.

P.S. I hesitated about the Math.stackexchange and physics, but assumed that this one is more applicable but please feel free to move it to math if you think it is better

Selene Routley
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Salvador Dali
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    This question appears to be off-topic because it is about biology (and might belong on http://biology.stackexchange.com/). –  Sep 30 '13 at 23:32
  • Possible duplicate: http://physics.stackexchange.com/q/72641/2451 – Qmechanic Sep 30 '13 at 23:36
  • I think it requires mathematical or physical knowledge, to solve it and I already suggested a possible way for a solution. Do not know how it can be related to biology (except that egg is a living being) – Salvador Dali Oct 01 '13 at 00:21
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    I would say this is on-topic, because it's ultimately about scaling laws for physical properties. Are people really saying that half of Galileo's Two New Sciences is not a fit topic for a physics-based community? – N. Virgo Oct 01 '13 at 05:39
  • Voted to re-open. There are physics considerations here. My answer is essentially the bare bones: and it partly is the need for gas diffusion across the egg that is the answer. The need for the baby to break out - well that's not easily further studied with physics, but there is likely more to be said by someone with detailed knowledge of gas diffusion. – Selene Routley Oct 01 '13 at 09:27
  • @SalvadorDali I added the diffusion tag to your question. It might be worth asking as a question about gas diffusion. You should be able to estimate the oxygen needs of a chick just before hatching from metabolic data (the energy needs tend to be roughly proportional to mass, whatever the animal, at least with "higher" ones like birds or even reptiles) on say Wikipedia - then pose the question as a gas diffusion one. – Selene Routley Oct 01 '13 at 09:35
  • @WetSavannaAnimalakaRodVance thank you, very much. It was hard for me to find appropriate tags – Salvador Dali Oct 01 '13 at 11:07
  • an egg does not need to have air diffusion. The embryo gains all of its nutrients and oxygen from the yolk and egg-whites while it develops. There is a small air-filled sack in one part of the egg that is pierced when the youngling is ready to hatch and that air is capable of sustaining it until the egg is open. Thus, the size is not determined by the air needs of the embryo. It is determined by its final size. – Jim Oct 10 '13 at 13:29

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This question should be posted on biology stack exchange, because the limiting issues turn out to be biological rather than physics.

For an outside-the-mother egg (i.e. a laid one rather than one, say, kept inside the body of a viviparous snake or even the ovum of a mammal), your reasoning is very sound physics and your ideas on gas exchange are very much on the right track, but it turns out not to be the surface area to volume ratio that limits an egg.

It's simply the mechanical strength of the shell. The shell cannot be too thick - otherwise there wouldn't be quick enough gas diffusion across it, although this turns out to be the lesser issue. The main one is the need for the baby to break out.

We know this because ostrich eggs and those of hugely bigger creatures (i.e. sauropod dinosaurs - at least all the ones we've found and can be sure which animal they are from) are pretty much the same size and have very like shell thicknesses.

My source is David Attenborough videos and my seven year old daughter - although the latter is highly reliable, I don't know her primary sources. So, like I said, this would be a good question to post on biology stack exchange.

Selene Routley
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  • My answer is essentially the bare bones: and it partly is the need for gas diffusion across the egg that is the answer. The need for the baby to break out - well that's not easily further studied with physics, but there is likely more to be said by someone with detailed knowledge of gas diffusion. – Selene Routley Oct 01 '13 at 09:28