Exobiology: The Origin(s) of Life on Earth

Exobiology was the original term given to the sciences central to the question of life-in-the-Universe. It’s now been largely replaced by Astrobiology, but I’ll stick with the original. To investigate life-in-the-Universe one needs to ponder the origin of life, and the only origin we’re certain of was the origin of terrestrial life. The origin of life happened naturally at least once and probably many times in diverse locations.

Life, even microbial life, is still very, very complex (try making a microbe from scratch if you doubt it). The fact that life arose from scratch on Earth within a very, very short span of geological time after the planet formed is a bit suspect IMHO.

The major reason for that is that in the early days of the formation of our solar system and of course Planet Earth, there was a lot of loose debris around flying around in all sorts of orbits. These bits and pieces would sooner or later impact one of the larger (planetary) bodies still forming and growing by the means of those very impacts. The orbiting large planetary objects would sweep up a lot of the rubble. Over time, the density of the rubble decreased, but to this very day there are still bits and pieces yet to make impact and call a planet home. We often see tiny bits of this left over rubble as ‘shooting stars’ in the night sky, but now and again a really large chunk can strike home, as the dinosaurs found out the hard way.

.

Anyone who doubts that there was a massive bombardment of the planets by large chunks of rubble need only look at the saturation of craters on the Moon or the planet Mercury or even Mars and many of the larger moons of Jupiter and Saturn. Heavily cratered objects have one thing in common – little or no atmospheres and active geology to erode and erase the remains of these impacts from multi-billions of years ago. Earth has an active geology and an atmosphere and lots of erosion so we find relatively little trace of that early intense bombardment locally. But, were it not for those processes, Planet Earth would resemble the cratered Moon.

Now, what’s the fate of early life forms when large chunks of rubble after rubble after rubble slam into their environmental abode? Poof – that’s what. Given that the origin of life isn’t easy (otherwise our biologists and biochemists would have created life in a test tube from scratch by now), it’s unlikely that life arose locally on Earth – went poof because of impacting rubble – arose again locally and naturally – went poof again – arose – poof – arose – poof, etc. So, is there another possibility?

What if Earth were seeded by microbial life forms already in existence from space (or deliberately seeded by an advanced extraterrestrial civilization as the Nobel Prize winner Francis Crick has proposed)? Now I realize that just puts off the origin of life question to another time(s) and place(s). However, given the vastness of the cosmos is far greater than that of our finite globe (Planet Earth), and given that the cosmos existed for vastly longer periods of time before our sun, solar system and home planet came into existence, such additional time and space easily turns the improbable into a near certainty. And once established somewhere, then life could spread throughout that time and space, until it reached us.

Earth arose billions of years after the universe and our galaxy had evolved, ample time for life to have arisen elsewhere, and seed the early Earth. This is the concept of panspermia. We know that comets, meteors, and the cosmic dust of outer space are chock-o-block full of complex organic molecules. We know that simple terrestrial microbial life can survive the outer space environment if suitably shielded – and it doesn’t take much to do the shielding. We know that surface bits from planets/moons can be ejected into space, carry a cargo of microbes, and land on another planet, even eons later with the microbes still viable. Of course 99.999% of all such microbial life will be doomed to forever wander in space or crash onto a cold surface of a planet with no atmosphere or water, or plunge into a star, etc. But, sheer numbers will insure that now and again some microbes will land on a hospitable abode and be fruitful and multiple and evolve. The interesting bit is that if then, then now. And thus panspermia will be happening today. Certainly some meteorites which have impacted Earth have inside them ‘organized elements’ suggestive of microbial structures – the Murchison Meteorite from Australia is one such stone from space; another was the famous 'rock from Mars' [known as ALH84001]. On the sceptical side, the problem is that such ‘organised elements’ could be just terrestrial contamination as there are often lengthy time periods between fall, discovery and analysis. As an aside, if Fred Hoyle & Chandra Wickramasinghe are correct (and I believe they are), microbes (bacteria/viruses) impacting Earth today are largely responsible for some select/various disease epidemics/pandemics, past present, and no doubt future.