@John_Harshman, take a look at this:
Eat your magnesium
Those linchpins Bray yanked out and replaced were metal ions (atoms with charges, in this case positive).
In today’s ribosome, and in the whole translational system, they are magnesium ions, and Bray’s experiment replaced them all with iron ions and manganese ions, which were overabundant on primordial Earth. Williams and Jennifer Glass, the principal investigators in the new study, also had their doubts this was doable.
“I thought, ‘It’s not going to work, but we might as well try the moonshot’,” said Williams who has led similar work before but on simpler molecules. “The fact that swapping out all the magnesium in the translational system actually worked was mind-boggling.”
That’s because in living systems today, magnesium helps shape ribosomes by holding them together. Magnesium is also needed for some 20 additional enzymes of the translational system. It’s one reason why dietary magnesium (Mg) is so important.
“The number of different things magnesium does in the ribosome and in the translational system is just enormous,” said Williams. “There are so many types of catalytic activities in translation, and magnesium is involved in almost all of them.”
As I recall, one of the examples from @pnelson’s test (Nelson's Test of Common Descent Comprehension) was about the type of ion in a protein. I remember responding to him that it is fairly easy to swap different metal ions in and out of a protein, so I expected there be a lot of homoplasy. Do you remember that example?
Of course, it is far more surprising that this worked for the ribosome, swapping all of them out at once. I don’t know if I would have predicted it. And on reflection is it really that surprising?