Comets and life 4


Updating Comets and Magic Universe

Did comets spark life on Earth?

Part 4: Life footloose in space

In Part 1 of this series, I mentioned that in Comets, written 30 years ago, I made fun of propositions from the astrophysicists Fred Hoyle and Chandra Wickramasinghe about viable entities living in comets and being delivered ready-made to the Earth, scattered from the comets’ tails. What follows fulfils a promise to look at Chandra’s present ideas — I hope with an open mind.

To back-track a little, there’s a 100-year history of eminent scientists, driven by despair about explaining the very improbable chemistry of life by home cooking on the Earth, suggesting that life came from elsewhere. Of course, their scenarios didn’t explain the origin of life, they merely transferred it somewhere else. Out of sight, out of mind, perhaps.

  • 1907 Svante Arrhenius (yes, the CO2 warming pioneer) suggested that bacterial spores escaped from an alien planet, were driven through interstellar space by the pressure of sunlight, and revived when they reached the Earth.
  • 1971 Francis Crick (yes, of DNA fame) with Leslie Orgel proposed that intelligent beings in another part of the Galaxy spotted the Earth as a suitably wet planet and sent bacteria in a spaceship to seed it.
  • 1979 Fred Hoyle (yes, celebrated for the origin of the elements) with Chandra Wickramasinghe said that life on Earth began in comets, and diseases still come from them.

It was hard not to chuckle over their book Diseases from Space, because Hoyle and Wickramasinghe’s account filled the sky with germs, in a distant echo of the old superstition that comets portended plagues.

John Gadbury (1665) linked comets and catastrophes -- "Famine, Plague & Warrs" In actuality, bubonic plague afflicted London following the depicted 1664-5 comet. Obtained from the Royal Astronomical Society, this is an illustration in N. Calder, Comets: Speculation and Discovery.

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Artificial life


Predictions revisited

Forecasts and fears about artificial life

Today’s news of Craig Venter’s success in fashioning a new species of bacterium, with completely man-made DNA, propels me to the bookshelf to recall how this breathtaking event was anticipated with some trepidation.

“Fried-egg” colonies of (a) the synthetic bacterium Mycoplasma mycoides JCVI-syn1.0 and (b) the natural Mycoplasma capricolum bacterium that provided the cytoplasm but had its DNA replaced. The blue colour in (a) is created by a protein coded in the new DNA that reacts with a chemical in the agar base. Without that gene the colonies of the unmodified recipient bacterium remain white (b). From Gibson et al. Science, see references.

In brief, as reported online in Science magazine, Venter’s team designed, synthesized and assembled a DNA chromosome. They transplanted it into a bacterium to create novel cells controlled only by the synthetic DNA, and capable of continuous self-replication.

Anticipations of manipulated life

My personal favourite among the projections of genetic engineering has for long been that of the physicist Freeman J. Dyson, with his idea of breeding gigantic trees capable of living on comets, to provide human habitation even in the outer Solar System.

But if you google “genetic engineering” you’ll get 5.4 million offerings, or 2.2 million for “bioethics”. Old books on my shelf have many pages on the future manipulation of life and its possible risks. To be reasonably brief, I’ve picked a possibly useful overview of issues anticipated a quarter of a century ago. It’s from The Green Machines, which was written as if looking back from 2030 and published in 1986.

In Aztec times in Mexico, people made biscuits out of mats of cyanobacteria called Spirulina, which they harvested from alkaline lakes. By the 1970s Spirulina was known to be exceptionally rich in protein, and harvesting resumed in Mexico. Italian microbiologists discov­ered that they could prolong the growing season for Spirulina by cultivating it in polyethylene tubes, and they reported pro­duction rates of 50 tons per hectare per year-roughly ten times the yields of ordinary crops. Doing without sunshine, Imperial Chemical Industries grew bacteria (Methylophilus methylotrophus) on methanol and marketed them as Pruteen.

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