h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

If the bacterium can survive that long...
It could cross the galaxy on a meandering planetoid or rock which one day plunges into a world which was capable of supporting life whereupon it could awaken and spawn a whole new world of life.

Is it therefore possible that life did not originate on earth?

It is an idea which has had many people wondering. Did the building blocks of life - amino and nucleic acids - come from outer space.
It is within the realms of possibility that it happened and the earth was seeded from a passing comet or meteor crash. This could be wrong and those building blocks could have formed in the chemical rich early oceans and with the right energy input actually have become self replicating.

Bit dificult to recreate the conditions in the lab to test the hypotheses

Another interesting thought is that everywhere we have looked on earth that is even remotely capable of supporting life we have found it...deep sea thermals, underground lakes, deep within glaciers etc.

If this and the seeded planet theory are put together then there is a very real possibility that the galaxy is absolutely teeming with life. Maybe this seti thing is more than just a pretty screensaver after all

Personally, I don't think it looks that pretty

In about 250 million years time, I will be unpacking the boxes in my attic, and find the book by Fred Hoyle. He was a mainstream astronomer and scientist, and wrote a book suggesting that bacteria arrive here as space dust.

He wrote the book pre-AIDS, but he suggests that one of the reasons we get "new" diseases, an indeed diseases localised to one continent, in the way syphalis and typhoid were, is that the viruses and bacteria which cause them dropped in from space.

This is more plausible than it sounds. Bacteria and viruses don't usually cause diseases. In other words a 'flu bug's raison d'etre is not to cause 'flu, it is to live and breed. The 'flu is incidental to the virus. Diseases are mainly caused by the body's reaction to those bacteria and viruses doing their own thing. This is one of the reasons why most disease symptoms manifest in the immune system somewhere. We get fevers because a higher temperature kills some bugs. The tonsils are part of the immune system, and they get inflamed when the immune system is working hard. Sickness and the runs (I won't even attempt the d-word!) are the body eliminating things from the digestive system; coughs and sneezes are the body eliminating stuff from the nose and lungs; and pus is the body eliminating stuff from wounds.

There are certainly viruses and bacteria which attack the body directly - gangrene springs to mind. I live in Gloucestershire where we had an outbreak of "flesh-eating bug" about 4 or 5 years ago. Basically bacteria in an infected wound were damaging the flesh at a rate which could be measured in hours. Literally. Our GPs best friend lost a leg. He had a wound in his foot, which was painful and inflamed. I didn't sound serious, and the ambulance they called was diverted to another case. By the time he did get to hospital a few hours later it was too late to save the leg.

And of course there are a huge number of bacteria and viruses which have no effect on people at all, but go for animals, or plants, or other bugs in water or the soil.

Another intriguing thing from the book was that when microscopic space dust was examined and found to contain substances that looked like DNA, the space scientists insisted that it couldn't be DNA. They knew their procedures meant that it was space dust, and therefore not contaminated. Life scientists insisted that it must be a contaminated sample, because it sure did look like DNA.

We may all be made of star dust in more ways than one.

I'm not sure that diseases such as AIDS dropped in from space, because they tend to have a fairly stable host community within which they do no real harm and only cause problems when they cross species.
This degree of mutual adaptation between the "disease" virus/bacterium and its host requires a great deal of time over which to eveolve.
A more likely (IMHO) occurence is that less complex building blocks than DNA are raining down from space constantly, and that under the right circumstances these can join to form proto-life but the existing lifeforms have all the niches covered so the new lifeform cannot get established. Of course, if the lifeform lands on a planet without a fully formed ecosystem it might gain a foothold.

On the subject of AIDS - researchers have been digging up dead French Legionnaires, and have discovered that the earliest known AIDS victims were abotu 100 years ago.

Basically they went back through the military and missionary records in Africa, looking for people who died of the right sorts of illnesses, and whose bodies could be located, and dug them up and ran tests on them.

Increased mobility from the 70s onwards meant that it was no longer in isolated pockets but able to spread. It reached two very sexually promiscous population groups in the late 70s: American Gays, and African road hauliers.

Does the "Panspermia Theory" ring a bell for you? I think that's the name of the theory about planets being seeded with life from space. I don't know if it's the name of Hoyle's book though.