Gina and I have been kicking this idea around for a while now, so I thought it might be worth a blog post. The eventual discovery of another life genesis event (life on another planet) is one of the underlying goals of space exploration (among others). What if Earth had experienced multiple life genesis events? Then maybe we could learn some of the general principles that might apply everywhere in the universe, by studying life here on Earth. At least until we have life on another planet to study. At first that idea does not seem to be supported by the evidence we have, but let’s look a little closer at the idea.
We know that conditions on Earth supported the genesis of life at least once because we’re here.[1] Although it’s possible, it would seem very peculiar if these conditions required for life to start[2] only existed once at a specific location over a relatively short period of time. Our experience with the universe shows that it just doesn’t work that way.[3] If these conditions existed at one place on Earth, it seems highly likely that these same conditions would have existed many places on Earth and probably over some geologic period of time. If this is the case then it would seem highly unlikely that life would have started at only one specific time and place. It would seem more reasonable that life genesis events occurred in multiple locations and over some extended time duration. So if this were the case, why don’t we see life from multiple genesis events on Earth today?
Perhaps the chemical reactions that make life only occur with a limited set of organic molecules. And perhaps DNA and RNA are the only molecules that lend themselves to coding for living systems. That being the case, wouldn’t life from one genesis event look a lot like life from other genesis events? Granted, we only know of one instance of life and it is carbon based and uses DNA and RNA to encode for living systems. We have a sample size one, so we don’t have enough information to make those assumptions without more data from other places in the universe. However, we are not likely to have this information for quite some time yet, so we’re left with speculation.
We do know that if something can occur in one place and time in the universe then it is likely to occur in other places and times given the same conditions. This is an underlying precept of our science, which allows us to observe something locally and expect it to occur elsewhere in the universe given the same conditions.
So the question then becomes, if there were multiple life genesis events on Earth why do we observe only one today? There are at least three possible scenarios to explain what we observe today:
- Early life competed and our kind survived. Life from other genesis events would have been overwhelmed and driven extinct. Since we are talking about early microbes, the fossil record for such a contest is likely to be very sparse if it exists at all. In this case we may never know.
- Life from different genesis events could be so closely related that we have not distinguished between them yet and they may coexist with us even today. If this were the case perhaps a careful study of various genomes might allow us to distinguish the subtle differences between the life from different genesis events.
- Life from different genesis events might have been so alike that it actually blended to form the type of terrestrial life we observe today, which only appears to be from a single genesis event because, well life is life no matter where it started. If this is the case, the differences between life from different genesis events would be very subtle and they could all exist within our modern global genome undetected. Studying the various species genomes that exist today may or may not allow us to distinguish which parts of a species genome came from different genesis events.
So where does that leave us? Well these are intriguing scenarios, and it does leave us open to speculate about other forms of life without ever leaving Earth, although it will still take life from another planet for us to begin seeing the overall guiding principles of life. In fact it may take knowledge of life from somewhere else in the universe to help us understand which of the three scenarios above may have occurred on Earth.
I find the second and third scenarios particularly intriguing. When designing a science fiction world it would be fun to explore these on a fictitious planet where the differences between the life resulting from various life genesis events are a little more accentuated than they are on Earth.
What do you think?
— Ron Evans (Dec 2015)
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[1] For the moment I’m ignoring the various panspermia proposals and assuming our form of life DID originate on Earth. So far, the evidence shows that ballistic panspermia might be plausible, but to my knowledge no evidence has been found to support that it actually happened.
[2] We don’t know exactly what the conditions required for life to start are, but whatever they are, they had to have existed on Earth at least at some point in the early history of our planet.
[3] If one star can form, this happens everywhere and trillions are formed. If organic molecules can form in one molecular cloud, they form in all molecular clouds that have similar conditions. If the proteins that are essential for life form in one tide pool, then they form in many tide pools under similar conditions.
Science Anywhere 