Sand was tested as a model of a common "impurity" that could have influenced the formation of thermal prebiotic protein. Increasing proportions of sand (0-16 g) in admixture with one set of reactant amino acids (1g), when heated at 175 degrees C for 1.5 h, resulted in increasing yields of polyamino acids of increasing size and color intensity; amino acid composition was not greatly affected. Similar results were noted for three of five other sets of reactant amino acids (8 g sand per g amino acids). In no case did sand prevent the amino acids from polymerizing. The results are interpreted to indicate a broader range of conditions conducive to the formation of prebiotic protein and to further emphasize that environmental parameters should be considerided in the experimental modeling of prebiotic processes.