The first known mention of the concept of panspermia was in the writings of the Greek philosopher Anaxagoras (500 BC – 428 BC), although his concept differs from the modern theory:
All things have existed from the beginning. But originally they existed in infinitesimally small fragments of themselves, endless in number and inextricably combined. All things existed in this mass, but in a confused and indistinguishable form. There were the seeds (spermata) or miniatures of wheat and flesh and gold in the primitive mixture; but these parts, of like nature with their wholes, had to be eliminated from the complex mass before they could receive a definite name and character.
In 1743 the theory of panspermia appeared in the writings of French nobleman, diplomat and natural historian Benoît de Maillet, who believed that that life on Earth was "seeded" by germs from space falling into the oceans, rather than life arising through abiogenesis.
The panspermia theory was rekindled in the nineteenth century by the scientists Jöns Jacob Berzelius (1779–1848), Lord Kelvin (William Thomson) (1824–1907) and Hermann von Helmholtz (1821–1894). Lord Kelvin declared in 1871, "[W]e must regard it as probable in the highest degree that there are countless seed-bearing meteoric stones moving about through space. If at the present instance no life existed upon this Earth, one such stone falling upon it might, by what we blindly call natural causes, lead to its becoming covered with vegetation."
In 1973 the late Nobel prize winning British molecular biologist, physicist and neuroscientist Professor Francis Crick, along with British chemist Leslie Orgel, proposed the theory of directed panspermia.