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Thursday, June 2, 2011


The question of how life originally arose on earth is of particular significance both to those searching for extraterrestrial life and to those searching for habitable worlds which are devoid of life.

Mythology withstanding, there are four likely possibilities of how life first arose on earth.

The first is anomalous abiogenesis, meaning that life arose from non-life in a single instance, and that all life on earth descended from that unique prototypical life form.

The second is non-anomalous abiogenesis, meaning that when the conditions are correct life tends to occur spontaneously and ubiquitously. In this case, the two existing domains of prokaryotes (bacteria and archae) were of completely different abiogenetic origin, and presumably other independent forms of prokaryotic life existed at one time but were out-competed early in earth's prehistory.

The third and fourth are anomalous and non-anomalous panspermia. This is the idea that prokaryotic life arrived on earth from space, likely ensconced in meteorites. There is a substantial amount of material support for this theory, which this series will explore in some detail. Panspermia does not answer the the question of how life originated in the first place, but for our purposes that concern is frankly secondary.

It is also of course possible that terrestrial life arose both on earth and from space. But determining which contemporary organisms are native and which are descended from aliens may not be knowable until we have unequivocally extraterrestrial organisms to compare them to.

The essence of this question is simply this: how rare or ubiquitous is life in our solar system and beyond? And if life beyond our atmosphere is not rare, how exotic or mundane is that life? We are now, possibly, starting to have some answers to these questions. These answers, and their implications, will be the subject of the next several posts.


Regarding the next week or so of posting, I will be out of the state and away from any real computer for much of the next week. Will post as much as possible via Android phone; many apologies in advance for the typos. There will be many.


  1. I've noticed throughout this discussion (earlier posts, not this one specifically) you presume that we as a species are wise enough to leave inhabited worlds alone. Andromeda Strain fears not withstanding, I haven't seen much in human history or human current events to give me much hope here. Would love to hear you elaborate on this?

  2. I realize that our history (and current events) has not offered much in the way of hope that our first contact with extraterrestrial life won't look a lot like Avatar. My belief is that the combination of what you call the Andromeda Strain fears and presumed abundance of uninhabited worlds, plus a well-considered reflection of the actual results of earth-bound imperialism, might lead us to make better choices than we have to date.

    I fully recognize the inherent naivete of this belief.