In life on Earth, the prevalent form of amino acids is L-amino acids. While some D-amino acids exist, they are relatively rare in biological systems. The stereochemistry of L-amino acids is a fundamental aspect of living organisms' biochemistry.
In life on Earth, the predominant form of amino acids is L-amino acids. These molecules exhibit a specific stereochemistry, where the amino group is on the left side of the central carbon atom when written in a Fischer projection. The "L" designation refers to the left-handed arrangement. This preference for L-amino acids is a fundamental aspect of the biochemistry of living organisms.
In contrast, D-amino acids (where the amino group is on the right side) are relatively rare in biological systems. While some D-amino acids do exist in certain contexts, they are not typically found in proteins or the primary structures of living organisms.
Therefore, the correct answer is:
**b. D-amino acids**
It is noteworthy that in the context of life on Earth, the presence of D-amino acids is generally limited and not a predominant feature in biological macromolecules.