In this work, the biophysical requirements of microbial life and the mean global physical environment of Earth and Mars are compared to suggest potential habitable zones on both planets. On average, life on Earth is restricted to the troposphere up to 8 km above mean sea level. In the crust, life is limited down to 4 km below the surface while in the oceans is limited to 10 km below mean sea level. On Mars, a biophysical appropriate environment for extant life is the crust between 2 and 10 km below its surface. In general, a planetary environment with a near-surface thermal evolution far from 310 K implies a more restricted spatial distribution of life, a lower biomass and less biodiversity on a planetary wide scale.