The landing of the Philae probe on comet 67P/Churyumov–Gerasimenko last month has led to speculation that comets might have delivered the building-block elements of life to Earth — an idea anticipated by the French astronomer Camille Flammarion more than a century ago in his 1880 book Astronomie populaire.

Flammarion wrote of comets: “Their importance would be much greater still if they should be found to carry in them the first combinations of carbon, for it is probable that it was by these combinations that vegetable and animal life commenced on the earth and the other planets and thus these vagrant bodies might be the sowers of life on all the worlds!”