From Wired Science
Life on Earth could have grown from the broken remains of alien viruses that, although dead, still contained enough information to give rise to new life.
Scientists have speculated that life could have come to Earth from space — a notion called panspermia — since the 1870s, when Lord Kelvin suggested microbes could have ridden here on a comet or meteor. Others have suggested tiny organisms could cross the galaxy embedded in dust grains, which could be nudged from one planetary system to another by the slight pressure of stars’ radiation.
However, most astrobiologists think that same radiation spells a death sentence for delicate microbes.
“That essentially kills panspermia in the classical sense,” said astrobiologist Rocco Mancinelli of the SETI Institute in Mountain View, California.
But maybe not, says astronomer Paul Wesson, a visiting researcher at the Herzberg Institute of Astrophysics in Canada. In an upcoming paper in Space Science Reviews, Wesson argues that even if the actual microbes are dead on arrival, the information they carry could allow life to rise from the charred remains, an idea he calls necropanspermia.
“The vast majority of organisms reach a new home in the Milky Way in a technically dead state,” Wesson wrote. “Resurrection may, however, be possible.”
The key lies in how much genetic information survives the trip, Wesson says. An organism’s genetic information is encoded in the sequence of nucleotides in their DNA. This information can be measured in bits in the same way as computer processes. Bacteria like E. coli, for example, carry about 6 million bits of information in their DNA.
Random chemical processes couldn’t produce enough information to run even a simple cell. Over 500 million years, random molecular shuffling would produce only 194 bits of information, Wesson says.
One possible way around this paradox is the idea that life on Earth was seeded by biological molecules that already had a large information content that survived the journey even though the molecules themselves were killed.
Wesson is a bit fuzzy on how that information would translate to new, healthy living things.
“It must be admitted that all versions of panspermia suffer from a hole in our knowledge, concerning how to go from an astrophysically delivered entity which contains substantial information to one which has the characteristics of what we normally regard as life,” he wrote.
But he does pinpoint the virus as a good candidate for the vessel that carried all that information. Viruses are basically strands of genetic material encased in a coat of proteins and sometimes fats. They carry about 100,000 bits of information, and may have evolved independently from conventional cells. Suggestively, viruses seem to assemble themselves from particles of protein, without needing assistance from other molecules or specific genetic information.
The paper “looks good, and interesting, although of course highly speculative,” David Morrison, the director of the Carl Sagan Center for the Study of Life in the Universe, wrote in an e-mail. “The critical issue is whether the information in broken strands of nucleic acid could serve as the template for life on another world … since we know so little about the actual process by which life originated on Earth, who can really say?”
But Mancinelli, who was not involved in the new study, doesn’t buy it.
“Once you’re dead, you’re dead,” he said.
The paper neglected two other things that could kill cells or viruses on their way through the galaxy, Mancinelli added. Elements like potassium can decay over the millions of years it takes to cross the galaxy, adding extra damage even if the organisms are shielded from space radiation
“It’ll give off enough radiation that it’ll just chop up all the nucleic acids,” he said. “There’s no way the organism will survive.”
The other issue is that, especially in a vacuum, hydrogen and hydroxyl molecules get ripped off cells and combine to form water. This process, called dessication, “is more than just drying up,” Mancinelli said. “You denature proteins. You rip them apart, recombine them, and they no longer have any functionality. That can happen even if you’re in a rock.”
Life would have a better chance if it didn’t have so far to travel, he added.
“Going from Earth to Mars, not a problem,” he said. “Even going from Earth to Pluto, or from Pluto to Earth, not a problem. But once you start heading out of the solar system, it’s so far away that it takes a long time. That’s the thing, the length of time.”