This is pretty interesting. I’m reading Michael Chrichton’s Sphere for the first time and that has a lot of discussion of the ways in which alien lifeforms could differ from us.

The first organism able to substitute one of the six chemical elements crucial to life has been found.

The bacterium, found in a California lake, uses the usually poisonous element arsenic in place of phosphorus.

The find, described in Science, gives weight to the long-standing idea that life on other planets may have a radically different chemical makeup.

It also has implications for the way life arose on Earth - and how many times it may have done so.

More at the link.