Peptide length is also an important factor for the formation of ordered structural proteins. Structural watersoluble proteins have a hydrophobic interior and a hydrophobic exterior, resulting in a rigid configuration and fixed shape, which is only possible when a protein is sufficiently long. This may not have been possible on early Earth, as shorter peptides were more abundant. However, it is not impossible for some long peptides to have formed on early Earth, such as abiotically on mineral surfaces, although their ability to fold into a stable structure is still unclear. Nevertheless, it is much more likely that functional short disordered proteins might have emerged before longer ones, while longer structural proteins are thought to have evolved later from these short primitive disordered proteins. Given that long-folded proteins are not required for phase separation, as short RGG domains of IDPs in isolation. can coacervate in vitro upon RNA binding, it is relevant to further examine shorter proteins and peptides with respect to both primitive and modern phase separation, in hopes of connecting the two.