Spaceship Earth-II: the future of Earth's life

"The earth is going to die in 500 million years!" exclaimed my eight-year-old today. And I had to illustrate to her how this is well beyond the span of our existence. Sort of a deanthropocentric exercise in reverse.

But what of it? Fundamentally, we don't like to think that there's nothing left of us - ever. But does that need to be the case? Yes, the sun is growing hotter, but we have hundreds of millions of years of technological advancement before the Earth becomes uninhabitable. And think where we've come in just one hundred years.

Last week, I was talking through a thought experiment with Mark on this topic.

Space is prohibitively large; commuting is not really an option. Even at the speed of light, the nearest star system to our own, Alpha Centauri, would take four years' travel. And it's questionable whether there's anything habitable there. It's a binary (plus) system, and the gravitational flux of two nearby suns may not foster stability.

Further, our bodies evolved in gravity, and it's not clear we'd survive for extended periods in minimal gravity environments.

In Rendezvous With Rama, Arthur C Clarke posited a mammoth cylindrical body 50 kms long, with habitation on the inside. That's an overwhelming construction endeavour. I think there are easier options.


My suggestion is that to travel beyond the Solar System would take far more massive an environment than we could possibly build ourselves. It would be simpler to grab an existing body, and power that away somehow. As Mark pointed out, this is the Space: 1999 scenario, a science fiction series where the moon was torn away from Earth.

Possibilities include using something large from the asteroid belt, a moon from Jupiter or Saturn (such as Ganymede), or maybe something far out, such as that erstwhile planet Pluto.

Issues include heat, propulsion, gravity, retention of atmosphere, and other life-sustaining variables. By the time it's worthwhile thinking about it, I'd say we'd have the technology to allow us a few options.

This is the stuff of science fiction, certainly; plenty of options have already been canvassed in that milieu. Burrowing underground would provide sturdy shelter, although digging enough habitable space would be Herculean. Other options include domes on the surface - or terraforming.


Ah, terraforming. Rather what happened to our own planet. Microbial life has built up our current atmosphere and environment; we're just the evolutionary outcomes that could adjust to it. It took hundreds of millions of years to develop, but I think it's reasonable to anticipate we'll be able to engineer biological solutions that work faster.

However, out beyond the easy reaches of the sun, everything freezes. There would need to be both sufficient gravity to hold an atmosphere (or to be able to continually regenerate it), and heat sources sufficient to prevent that freezing. The latter would be most feasible through nuclear fusion sources - we haven't succeeded at this yet, but I can see no reason it won't come. It's what the sun uses.

Gravity is a matter of using a large enough body. Life on Earth is, of course, evolved for our specific gravity, and much more research is needed to understand how or whether current life forms could adapt to lower gravity, or whether we'd need to engineer alterations that would allow various forms to survive in a somewhat different environment.

Because we would want to take with us as much of the existing variety of life as we could. This could involve storing samples at the DNA level, for later development/unpacking using either technological or substitute development (incubation) methods. In any case, plants and animal life should be considered an essential part of our environment - our being - and taking that with us would not be at issue. Bacteria and viruses too, surprisingly enough. Bacteria are our microbial engineers, a fundamental tool of life. Viruses have helped us become what we are today, though infiltrating our germ lines, they have imparted in us the resilince - and functionality - that we possess today.

The Earth's variety of life evolved specifically because the amount of solar radiation both protects us from other stellar sources, and generates mutation by occasionally knocking around with DNA. Outside Earth's orbit, mutation would happen at a different rate, which we would have to account for. Lesser rates would not be an issue: we are now at the point of engineering our environment to overcome the 'need' for adaptive outcomes of mutation. Greater rates of mutation would necessitate careful screening to optimise outcomes.

Yet that begs the question: outside the Earth's specific environmental womb, would it be more beneficial to engineer adaption in ourselves, so that future generations can make the move more readily? The biggest barrier is ourselves: the fact that we are rather wedded to our current form, no matter how ill-adapted to space journeying. I suspect we would be more willing to put extra effort into optimising our environment, than to force evolutionary change on our own grandchildren.

I have great optimism that we will survive in the long run. Even if, to paraphrase Steve Kilbey, we end up as digital memory*.


None of this is a substitute for getting our own planet in order. But if we can succeed in that, we'll probably be well placed to survive past the use-by date of our planet.


*The Church: Fog, (1992 B-side to Ripple)
It hurts to think that in a hundred years
We'll all just be microfiche
Our names and the names of our songs
Cataloged and filed away

- however, compared to the fate of most of our ancestors, I'd be happy to survive in digital form.

Evolution: Some further thoughts on radiation and mutation

Radiation is "in part responsible for the mutation that occurs in all organisms"*. In fact, I've heard little to suggest that there are any other significant [non-anthropogenic] causes of mutation (see previous post on mutation here).

Humans have happened upon this Earth about halfway through the planet's habitable lifespan. Putting aside terrestrial sources of radiation (both artificial and natural - they don't seem to figure significantly on the whole), it has been frequently noted that our atmosphere protects us from a large amount of cosmic radiation, solar and otherwise. The implication is that our atmospheric and solar characteristics dictate the "steady" rate of mutation experienced by life on this planet, which facilitates a stable - or life-fostering - evolutionary pace. It's interesting to speculate on the different radiation scenarios, and their possible outcomes. Too much cosmic radiation and mutation rates may go too high for good species cohesiveness; higher life forms may not develop. Too little radiation may mean insufficient adaptability to the planet's changing environment - Earth's environment for one has varied quite substantially in many directions over its history.

Given that we inhabit one of a very large number of solar systems in the outer reaches of our galaxy, it's plausible that other planetary systems may have developed along a similar path to ours. Speculation on how likely it is for there to be life anywhere near us would be a function of the density of our galactic neighbourhood, the likelihood of a similar solar system developing, and the range of tolerance of radiation for viable mutative life to evolve.

On an anecdotal basis (given the results of SETI to date), the suggestion is that there is nothing close by. But it would remain interesting to attempt the sums on the range of radiation that would foster an evolving biosystem.



*101 Key Ideas: Genetics, Jenkins, M (2000); Hodder & Stoughton, London.
This book has got some surprisingly sloppy writing and at least one incorrect diagram. But from time to time its descriptions give particularly useful insights.

Evolution: causes of mutation

Mutagens are those factors that cause mutation. Most sources list radiation and chemicals as the two types of mutagens. Some sources also add that there is a steady (background) amount of "natural" or "spontaneous" mutations. I haven't read enough about it to know whether this can be ascribed to a "natural" [terrestrial] amount of background radiation.

It is important to note that the implications of mutation - change in the original DNA base sequences of an organism - differ depending on whether the cell affected is a somatic or a germ cell. A mutation that occurs in a somatic, or body, cell will not affect heredity; the most notable outcome for a somatic mutation is cancer.

A mutation can be inherited if a) the DNA change has no significant impact on the viability of the cell, and the reproduction process, and b) it occurs in any of several types of germ cells - ie those cells that eventually give rise to the gamete egg or sperm.

Radiation in the ultraviolet wavelength can sometimes penetrate cells, and get absorbed by DNA, causing structural damage. Ionising radiation, which has a shorter wavelength than UV, is so called because it can knock electrons out of atoms, producing ions - which are more easily capable of taking part in chemical reactions. All organisms experience a small level of background radiation, which in origin can be either cosmic, solar or terrestrial (from either naturally occurring radioactive material or, more recently, human-originated).

At the DNA level, mutations can result in insertions of extra information (as base pairs), deletion of some pairs, or miscopying, such as transposition of sequences of base pairs.

Again, I wonder if "background" levels of ionising radiation are responsible for "background levels" of mutation. I would be interested to hear if any experiments have been done to establish causality: this could, for example, involve sufficiently shielding from background ratiation a sample of DNA-bearing organisms with a reasonably short generational span.