Non-biological processes, on the other hand, do not usually distinguish between L and D variants. This step, called chiral selection, is crucial to forming chainlike molecules of pure L amino acids. Hazen and his collaborators performed a simple experiment. Most minerals are centric, that is their structures are not handed. However, some minerals display pairs of crystal surfaces that have a mirror relationship to each other.
Calcite is one such mineral.
It is common today, and was prevalent during the Archaean Era some 4 billion years ago when life first emerged. The real challenges now lie in selecting and concentrating L-amino acids, and then linking those molecules into chainlike proteins. Our experiments demonstrate that crystal faces of calcite easily select and concentrate the amino acids. Experiments now underway will see if the calcite also promotes the formation of amino acid chains.