Some of Archea also live in less extreme environments. Could somebody check it.
indicate that, although they can be extremophiles, they aren't necessarily always extremophiles. I've made what I hope is an appropriate change to the wording.
Also what is meant by "are very old"? Compared to what? Is the intended sense of this that their phylogenetic divergence is ancient?
There's nothing that would suggest that they are any older than Bacteria. They're of course much older than Eucaryota, but Bacterias are also. (Unless I missed some recent findings about Archea)