Sawkins, F. J. (1978). The evolving earth. Macmillan.
Cita Chicago (17th ed.)Sawkins, Frederick J. The Evolving Earth. Macmillan, 1978.
Cita MLA (9th ed.)Sawkins, Frederick J. The Evolving Earth. Macmillan, 1978.
Atenció: Aquestes cites poden no estar 100% correctes.