Ammonium ion concentration in the primitive ocean.

If ion exchange on clay minerals regulated the cationts in the primitive ocean as it does in the present ocean, the pH would have been 8 and the K(+) concentration 0.01M. Since NH(4)(+) and K(+) are similar in their claymineral equilibria, the maximum NH(4) (+) concentration in the primitive ocean would also have been 0.01M. An estimate of the minimum NH(4)(+) concentratin is 1 x 10(-3)M, based on the reversible deamination of aspartic acid and the assumption that aspartic acid is necessary for the origin of life. The rate of this nonenzymic deamnination is rapid on the geological time scale.