Mars, Panspermia, and the Origin of life: Where did it all begin?

During the nineteenth century, when steady-state cosmological theories were in vogue, Lord Kelvin, Svante Arrhenius, and other eminent scientists believed that the transfer of life from one planet to another was a process made inevitable by the infinite extent and duration of the universe. This hypothesis, known as panspermia, subsequently fell out of favor, partly as a result of the acceptance of the Big Bang theory. Most efforts to understand the origin of life have since been framed by the assumption that life began on Earth.