On Wed, Nov 24, 1999 at 03:03:35AM -0800, Liam. A. Chu wrote:
> If it takes two supernovae to get (e.g.) Fe through U, maybe we _are_ the
> Elder Gods, such as there are. 4 Billion + 4 Billion + 4.5 Billion adds up
> about right, in Fermi number terms.
Heterocyclic carbon chemistry really doesn't get on well with elements from the second transition metal series (or indeed most elements heavier than iron). Sure there are a few enzymes that use vanadium or iron, but in general heavy ions with lots of holes in their outer orbitals wreak havoc on hydrogen bonds.
As successive generations of nucleosynthesis increases the proportion of things like lead and uranium in the mix from which planetary systems are formed, can we anticipate the closure of the "window" within which terrestrial planets provide conditions suitable for the evolution of carbon-chemistry based life? So we may not only be nearly the first kids off the starting block, but not that far from the last generation before the neighbourhood turns into a toxic waste dump.