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Imagine a planet similar in chemical composition to Earth. Could life evolve there for which iron in its elemental form (not necessarily oxides) was toxic? Could animal type lifeforms exist that had somewhat similar respiratory/digestive systems to Earth animals in that they consumed carbon and oxygen, but have a non iron based method of transportation of oxygen. Basically, is it actually feasible to have non-iron based blood (I know Mr. Spock does but I'm not sure how plausible that really is), taking into account that resources are available in a similar proportion to Earths.

Furthermore, if an intelligent species arose, would it have an impassable hump in technological progress to get to a level of technology beyond modern day earth technology without relatively easy access to an abundant metal. That's not to say that iron or steel couldn't be used, but it would be used cautiously and not in everyday items. I realise they could use bronze for blades and other tools, but it is expensive and that aluminium is very abundant and can make a good substitute for iron or steel in many applications, but would you ever really get access to it, if you didn't have the iron and steel to make industrial machinery to extract it? What lines of material technologies might they pursue?

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    $\begingroup$ "Basically, is it actually feasible to have non-iron based blood" - squid and octopus use copper, resulting in having blue blood. $\endgroup$ – DoubleDouble Oct 27 '15 at 18:40
  • $\begingroup$ Iron <i>is</i> toxic. It's possible to overdose on iron tablets and die. Eating iron filings could have the same effect. The reason that iron doesn't seem that toxic is that iron doesn't crumble without a lot of help. So touching or even licking iron doesn't cause toxicity. $\endgroup$ – Howard Miller Oct 27 '15 at 23:23
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From what I understand (which could very easily be wrong), iron is already toxic as is to humans in the right forms and dosage. As said I could be wrong and likely I am but I've often heard the idea that pretty much anything can be lethal in the right quantities.

I've tried looking into something similar myself previously and found very little that actually gave a definitive answer. You'd likely be safe making it up as we have no way of knowing how another form of life would exist, let alone how it reacts to certain elements. Many sci-fi shows and movies have opted for silicon based life as it was one of the elements Carl Sagan thought would make sense for another form of life (alongside germanium).

As for having blood without iron, there is some life on Earth that uses copper instead of iron to move oxygen around. I'm not sure how well this could apply to your question though.

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Iron being toxic

The table of elements shows us that the natural poison for a creatures base element can be found 2 down and one to the right. Examples; carbons poison is arsenic, Nitrogen's poison is selenium and Boron's poison is Germanium. Unfortunately for you iron does not match as a poison for any element never mind one that can support life. So iron cannot be poisonous as far as I can tell. I am not an expert on alien bases as far as elements go, my specialty is evolution so this is all I can help you with. Here is a link to a paper about alien blood

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    $\begingroup$ Source for that two down and one to the right rule? $\endgroup$ – Dan Smolinske Oct 27 '15 at 20:30
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    $\begingroup$ @Dan Smolinske: I remember it from science fiction comedy Evolution. I think it is a joke. $\endgroup$ – BartekChom Oct 27 '15 at 20:35
  • $\begingroup$ Are you sure its a joke? $\endgroup$ – TrEs-2b Oct 27 '15 at 20:49
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    $\begingroup$ Practically yes. This does not make sense. There are many more elements poisonous for humans than only arsenic (Pb, Hg and many other heavy metals). Nitrogen based life itself hardly makes sense. Arsenic is poisonous because it replaces phosphor. $\endgroup$ – BartekChom Oct 27 '15 at 21:58
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    $\begingroup$ @LordofEden So where did you hear about it? Was it from Evolution? $\endgroup$ – HDE 226868 Oct 27 '15 at 22:59

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