• Corpus ID: 13918836

Panspermia Revisited

@inproceedings{Gribbin1999PanspermiaR,
  title={Panspermia Revisited},
  author={John R. Gribbin},
  year={1999}
}

• J. Gribbin
• Published 1 September 1999
• Physics, Geology

The discovery of evidence for life on Earth more than 3850 million years ago (1) naturally encourages a revival of speculation about the possibility that life did not originate on Earth, but was carried to the planet in the form of microorganisms such as bacteria, either by natural processes or deliberate seeding of the Galaxy by intelligent beings. This idea, known as panspermia, has a long history (2, 3), but it is curious that in recent decades astronomers have tended to dismiss the possibility of panspermia on the grounds that microorganisms could not survive the damage caused by ultraviolet radiation and cosmic rays on their journey out of a planetary system like the Solar System (4) while some biologists (5) have argued that it is impossible for life to have emerged from simple molecules in the limited time available (now seen to be substantially less than 1000 million years) since the Earth formed. This has led Crick, in particular, to argue that the seeds of life were indeed carried to Earth (and presumably other planets) protected inside automated spaceprobes, a process he calls directed panspermia (6). Recently, however, Wesson and his colleagues (7,8,9,10) have pointed out a way in which biological material could escape from a planet like the Earth orbiting a star like the Sun by natural processes, and survive with its DNA more or less intact. The problem is that although microorganisms could escape from the Earth today, their biological molecules would quickly be destroyed by radiation in the near-Earth environment. Bacteria shielded inside fine grains of material such as carbon could survive in the interplanetary environment near Earth, but would then be too heavy for the radiation pressure of the Sun today to eject them from the Solar System. The solution is to argue that suitably shielded microorganisms can be ejected from a planetary system like ours when the star is in its red giant phase. This makes it possible for natural mechanisms to seed the Galaxy with viable life forms – and even if the biological material is damaged on its journey, as these authors point out, even the arrival of fragments of DNA and RNA on Earth some 4000 million years ago would have given a kick start to the processes by which life originated here. The remaining puzzle about this process is how the grains of life-bearing dust get down to Earth. In their …