It has been far too long since I posted about microbes on this blog. As a brief recap, prokaryotic microbes – bacteria and archaea – outnumber (and outweigh) all other forms of life on this planet by a wide margin. I have long held that those microbes living within the earth – either lithospheric or sedimentary – constitute the largest proportion of these microbes.  I’ve had this opinion since I first wrote a letter disputing the notion that plants were the predominant form of life to the SAT board (at around 16) when they had the temerity to mark me wrong for saying bacteria instead of plants (bacteria and archaea was not an option).

For a long time, this has been in dispute by wiser minds than those assembling SAT tests, but for the most part the question has remained unresolved due to a lack of data. Prokaryotes are nearly invisible to most forms of microscopy, and so systemic reviews of frequency have had to wait for modern rapid gene sequencing and other techniques to arrive.

Research in the 21st August issue of Nature has shed some light on the matter. They were studying microbes that live in deep-sea sediments: microbes that live not on the ocean floor but underneath it, using a drilling vessel that had been repurposed from its original mission of finding more oil.

Data from this paper suggests that there are on the order of a million cells in every cubic centimeter of sediment 500m beneath the sea floor, or more than 50% of all microbial cells on earth. Additionally, the predominant form of these organisms is Archaea.

Now, I’ve already speculated that Archaea pre-dates bacteria and that the nucleus represents a primordial parasitism of an Archaea upon bacterial colonies (many bacteria, despite not being “multi-cellular”, live in aggregates that are, in fact, surrounded by another membrane.) I also believe in xenogenesis; that is, I believe life came to Earth from elsewhere, most likely Mars. Looking through my archives I don’t seem to have come out on this aspect publicly before, but my train of logic is simple:

1. Mars attained the temperatures and pressures needed, particularly surface temperatures around the triple point of water, when Earth was still a sterile molten cauldron. There’s abundant evidence that mars had surface water in its early history.
2. Our best fossil evidence suggests that microbial life arose on Earth practically as soon as the Earth was cool enough to allow liquid water to exist. While the measurement at these deep time distances is subject to wide margin of error, the margin of error is on the order of several million years, which is too short for most known abiotic processes to result in life.
3. Earth was under continual bombardment by fragments of Mars during this time.
4. Therefore, life came from Mars.

More specifically, I think Archaea came from Mars, and that bacteria are the “native’s” way of doing things.

Anyway, the fact that the pervasive form of life in subsea sediments are Archaea leads me to think that my hypotheses still holds.  There’s another issue of Nature that I haven’t quite gotten to yet that has more information about the biotic processes that allow life to continue down there, so watch this space for more microbial meanderings.