Primitive life can be schematically described as organic molecules processed by liquid water. Amino acids were most likely available on the primitive Earth, home-made from the primitive atmosphere or in hydrothermal vents. Import of extratemestrial amino acids may represent an alternative supply. Experimental evidence is given for selective condensation of amino acids driven by the hydrolytic power of liquid water. When hydrophobic and hydrophilic amino acids are forced to coexist within the same chain in liquid water, the duality generates interesting topologies such as stereoselective and thermostable P-pleated sheet structures. Polycationic alternating peptides containing lysyl and hydrophobic residues strongly accelerate the hydrolysis of oligoribonucleotides. The P-sheet geometry plays an determinant role in the observed chemical activity, as in contemporary enzymes. P-sheet forming peptide sequences may represent a support for primordial information amplification.