Measured Against Reality

Monday, August 28, 2006

What Would Alien Life Be Like?

Imagine that alien life was discovered on a distant world. What would it be like? It would look very foreign to us, beyond even the most active imaginations. However, there will be some things that would most likely evolve there too, making alien life at least somewhat recognizable.

I'm assuming a few things. First, that the life is not buried deep underground or at geothermal vents. Not only would these critters be hard to find, they wouldn't be as diverse as terrestrial life. I'm also assuming carbon-based life forms. Life may not always be carbon based, but I highly doubt that anything else exists.

Continue reading...1. DNA

Whether it’s actually DNA or some other molecule, life needs a genetic code. Without an accurately reproducible, readily translatable genetic code, life cannot exist, at least in any stable form. It’s certainly possible that alien chemistry could come up with something other than DNA, but there’s a good chance that DNA is simply the only viable organic molecule for the job.

It’s also vital that a carrier of genetic information accumulates errors and causes the organism containing it to mutate, otherwise evolution could not occur. So a molecule for life needs to be extremely reproducible, but also not so much so that it no longer evolves. It’s very likely that DNA will fill this role.

2. Plants and Animals

Once life gets started, it will almost certainly be similar to our bacteria: unicellular organisms eating organic molecules and eventually each other. But a world with just bacteria would not end up being very biodiverse, and given the small amount of nutrients that would be available on a planet that had recently evolved life, and that there would have to be some kind of nearby star for life to form at all, some form of cyanobacteria and eventually plant life would evolve. The light from a star is just too abundant a source of energy for life to miss, and without plants to turn its energy into biomass no higher life forms would evolve. As long as our hypothetical planet is fairly far along evolutionarily, there will be a plant/animal divide, although the occupants of each category may be nothing like what we’re used to, and things like fungi that don't fit well into either category will probably exist as well.

3. Sex

Exactly why sex evolved in the first place is a bit of a mystery, but the vast numbers of sexually reproducing compared to asexually reproducing life forms at the multi-cellular level indicates that it does have an advantage. It’s likely that recombination of genes allows evolution to occur more rapidly, giving sexual species a better chance at surviving changes in environment or filling an ecological niche.

Because of this it’s highly likely that multi-cellular alien life would have some form of sexual reproduction. It might not be something that we recognize as such, but it’s very unlikely that all forms of life would reproduce asexually.

4. Eyes

Estimates put the number of times eyes have independently evolved in the animal kingdom at around 30, and the time it takes to evolve them at around 100,000 years. Since they appear so many times and so rapidly here on Earth, it’s almost impossible for our alien animals to not be able to see. They’ll probably see light, since any star that is suitable for life will put out a lot of its energy around the visible spectrum, but this is not a given. Some animals see infrared or ultraviolet on Earth, it’s entirely possible that alien animals would see in these or other spectra too.

5. Ecological Niches

It’s very likely that the same kind of ecological niches that exist here on Earth will exist on alien planets. That means that there will be plants, nitrogen fixers, parasites, prey, predators, scavengers, and decomposers, along with a host of other things that will be specific to how life evolved there. For example, many insects survive on pollen, but if plants don’t pollinate on the alien world than that niche will not have to be filled, so there will be nothing like our pollinators. This means that we may find some truly extraordinary creatures doing some fairly bizarre things based on the niche they occupy, but there will be some basic ones (like the few I mentioned) regardless.

6. It will totally surprise us

As I learn more about evolution, it becomes ever clearer that life always does find a way to do something. When confronted with a problem, evolution will always find some kind of answer. Once abiogenesis occurs on some distant planet, evolution will take its patchwork, jury-rigged course, and its solutions to the problems it will encounter will be as fascinating as the ones here on Earth. (Of course, I know evolution is not any kind of active force, but it's easier to describe it as such.) I'd be excited for the day we find extraterrestrial life if I thought there was any chance at all of it happening within my lifetime. I hope those future scientists/space travelers enjoy it.

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