One of the deepest and most controversial questions of our time is that of the origin of life. In this public lecture a hypothesis is presented, according to which the temperature gradients existing in the earth - which led to plate tectonics and the formation of undersea thermal vents - also led to the evolution of life around these vents. Movies will be shown of experiments, in which all stages of this scenario are justified: how thermal gradients led to plate tectonics, to DNA amplification in thermal vents, to polymerisation of peptides at high pressure, and to the organization of bacteria. This mixture of physics, chemistry, and biology illustrates how life can originate without the intervention of the sun, driven only by geophysical thermal gradients.