Are we Martians?

Mars and the Earth have very similar rotation periods and axial tilts. Since the notorius ‘discovery’ of canals, Mars and its inhabitants have been a popular subject in science fiction stories. Later observations revealed a very thin atmosphere and low temperature, which make Mars a rather hostile place. Finally, the Viking landers showed a marred planet. Yet the possibility of some simple life forms cannot be excluded. In 1984 a meteorite was found in the Allan Hills region in Antarctica and labelled as ALH 84001 (Fig. 20.4). The piece of rock was estimated to be 3.9 Ga old. Chemistry of the meteorite shows that it had originated on Mars; an impact had thrown it to an orbit that brought it to the Earth. In 1996 a group of NASA scientists announced that the meteorite contained structures resembling fossilized microbes and compounds that could be products of living organisms, such as polycyclic aromatic hydrocarbons (or PAH) and magnetite. However, they can be produced by other processes, too. Not surprisingly, the results and the implications of Martian life caused a lot of skepticism. Only further Mars expeditions and possible in situ experiments can decide whether there has been life on Mars. In case there has really been life on Mars, there are several possibilities: Life originated independently on the Earth and Mars. Life originated only on the Earth and was then transported to Mars. Life originated only on Mars and was transported to the Earth. It seems that life on the Earth emerged almost as soon as the conditions became favourable. It has been argued that the life appeared even too quickly. This problem would be solved if life originated on Mars. The surface of the more distant and smaller Mars had cooled down faster to become habitable before the Earth. Thus life would have had more time to evolve on Mars, and was transferred to the Earth when conditions here became suitable. Thus our earliest ancestors could be Martian bacteria. Presently such considerations are, however, just speculations. The idea of life spreading from one celestial body to another is known as panspermia. The idea dates back to the antiquity, but its first serious advocate was the Swedish chemist Svante Arrhenius, who published a book on the subject in 1908. Of the later proponents, Sir Fred Hoyle was the most famous. Panspermia fit well to his cosmology: the universe had no beginning, neither did life, but had always existed. Thus the tough problem of the origin of life was neatly avoided. Now panspermia, in a certain more limited sense, begins to seem a little more possible theory. Primitive life forms can survive inside meteorites in the coldness and lethal radiation of the interplanetary space long enought to travel from one planet to another. Interstellar distances, though, are too long, and the probability of a meteoroid from one planetary system hitting another system is too low. It seems obvious that our life has originated here in our own solar system.