After many tribulations, my astrobiology bloggery is back up and running using Wordpress rather than Blogger because Blogger is completely unusable these days.  I've taken the opportunity of the move to make better graphs for my old posts. 

"The Solar System: Why Earth?"

Here, I try to look at our own solar system and what the presence of only ONE known biosphere, here on Earth, tells us about life and perhaps more importantly what it does not.  In particular, I explore what aspects of Earth make it special and I make the distinction between a big biosphere here on Earth that has utterly rebuilt the geochemistry and a smaller biosphere living off smaller amounts of energy that we probably would never notice elsewhere in our own solar system given the evidence at hand. 

Commentary appreciated.



Previous works:

Space and Time, Part I

Space and Time, Part II

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Advice solicited. Topics of interest I have lined up for upcoming posts include:

  • The history of life on Earth and its important developments
  • The nature of the last universal common ancestor (REALLY good new research on this just came out)
  • The origin of life and the different schools of thought on it
  • Another exploration of time in which I go over a paper that came out this summer that basically did exactly what I did a few months earlier with my "Space and Time Part II" calculations of our point in star and planet order that showed we are not early and are right around when you would expect to find the average biosphere, but extended it to types of stars and their lifetimes in a way I think I can improve upon.
  • My thoughs on how and why SETI has been sidetracked away from activities that are more likely to be productive towards activities that are all but doomed to fail, with a few theoretical case studies
  • My thoughts on how the Fermi paradox / 'great filter' is an ill-posed concept
  • Interesting recent research on the apparent evolutionary prerequisites for primate intelligence

Any thoughts on which of these are of particular interest, or other ideas to delve into?

Primates and eukaryotes would be good.


The short version before I get a chance to write more posts:

Primates appear to be an interestingly potentiated lineage, prone to getting smart when they get large, due to differences in brain development established 50+ megayears ago that make their brains much more impressive per unit volume than most larger mammals. The great apes other than humans actually seem to run into energetic limits to feeding their brains and have smaller brains than you'd expect for a primate of their size, while humans are right on the generic primate trendline. Birds are another potentiated lineage - their brains are about 6x as compact as a comparable primate brain.

Eukaryotes are really weird. The one thing that is incontrovertible these days is that the classic 3-domains-of-life idea, with eukaryotes and archaea as sister clades, is turning out to be wrong. Eukaryotes are turning out to have come from a fusion/symbiosis of a bacterium and something that fits entirely within the archaeal domain. Various people who are studying their origin and evolution have their pet models and hold to them too tightly and fight each other bitterly, though some things are finally coming out for sure. A lot of their weird features may come from particular population genetic selective pressures that come from competition between copies of the mitochondrial genome, and a lot of others may come from the fact that they invented sex and have low population sizes both of which allow types of evolution and genetic drift that you are much less likely to see in the eubacteria or archaebacteria, the two 'primary' domains (whose separation represent the deepest branch in the tree of life). But the fact that ALL eukaryotes have a huge constellation of weird traits with no intermediate forms means their origin was a weird event, and opinions vary on if that means it was a singular extremely unlikely event or if all those weird properties come logically from how they formed, and on if there was strong first-mover-advantage.

And, of course, our data on the breadth of life that exists on Earth is incomplete... I love the specialized journals on electron microscopy, now and then you see a paper where someone just sees something really bizarre and reports on what they saw without a clue as to what it is. If you want a really perplexing paper, take a look at this: (alternately ) "A Unique Microorganism from the Deep Sea"

I'm extremely interested in the last three of these especially the Fermi paradox one. Great essays.

CellBioGuy all your astrobiology posts are great I'd be happy to read all of those. This may be off the astrobiology topic but I would love to see a post with your opinion on the foom question. For example do you agree with Gwern's post about there not being complexity limitations preventing runaway self-improving agents?


I generally have very low confidence in singulatarian ideas of any stripe, 'foom' or non. Partially for sociological analysis-of-the-origin-of-singulatarian-and-related-ideas reasons. Partially for astrobiological reasons relating to the fact that nothing has ever consumed a star system or sent self replicating anythings between stars and my impression of the range of possible outcomes of intelligent living things that are not extinction or controlling the universe and the possible frequencies of things something like us. Partially because I think that many people everywhere misattribute the causes of recent changes to the world and where they are going and have short time horizons. Partially because I am pretty sure that diminishing returns applies to absolutely everything in this world aside from black hole growth.

I can't say I've read Gwern's analysis of computational complexity, but I do note that in the messy complicated poorly-sampled real world you can very very seldom actually KNOW enough to predict much of a lot of types of events with great precision.

I'd find all of these interesting, particularly the first three and the last.

I'm glad you're back.

My first attempt to list which of these I want most ended up being "all of them". In the interests of giving useful feedback, I think the most interesting ones are the problems with SETI (haven't heard anything about this but I also haven't been looking) and the origin of life (have heard about this but I suspect your post would be better than average).

Your response to CarlShulman makes me want more about eukaryotes too.

Have you ever seen this paper that claims a complexity analysis of the Viking lander experiment results can't be explained by chemistry alone? Interesting stuff...


Now I have!

I think their case is weak but it is something to continue to be considered when analyzing any new data. There's weird soil chemistry there for sure, a good deal of which might be explicable from the interaction between perclorate and small amounts of organics, but the amount of data is tiny and I would not rule out soil microbes. A lot more work has to be done before you can say much with confidence.

All of these look very interesting. I am particularly interested in the 2nd and 3rd topics.

might want to keep an eye out for a Mars global dust storm too...

"The paper noted that conditions in the current Mars dust-storm season are very similar to those for a number of years when global storms occurred in the past."

Shirley's 2015 paper in the journal Icarus