An attempt is made to reconstruct some features of the past history of the earth's climate using a 1-dimensional planetary model. Starting at 250 M yr ago to the beginning of the quaternary glaciation and taking into consideration the evolution of the sun's luminosity and paleoclimatic as well as geophysical data, possible evolutionary pathways are drawn. The main point of the results is that regardless of the details of the pathway followed, the infrared cooling coefficients and the heat transfer coefficient necessarily must have been evolving. Some arguments are advanced, determining the direction of this evolution.