Broadcasting to all Star Trek fans out there...
All you Trekkies, yo !
Have you already forgotten that wonderful episode in Series 1 (with Bill Shatner and Leonard Nimoy) where thay land on a planet where all life is based on silicium instead of carbon?
Where plants grow as crystals and sand is actually insects?
The authors realized that in the Table of Elements Silicium sits right under Carbon - hence it works just like carbon, chemically speaking, only that the "chemical offspring" will be different.
In our case, plants like crystals, flying sand and rock-like earthworms.
Here on our planet, our blood is red because hemoglobin is chemically based on iron.
But in mussels, octopus and squid, blood is based on copper.
They are much stronger, but run out of wind much earlier.
That is why a scuba diver will, if lucky, successfully "win" when wrestling an aggressive 5ft. squid
http://en.wikipedia.org/wiki/Humboldt_Squidhttp://www.bbc.co.uk/programmes/p008py6fhttp://www.bbc.co.uk/nature/species/Humboldt_SquidSo arsenic-based DNA? Why not ? After all, haven't we got poisonous plants from which we draw life-saving medicines?