The Earth Has Not Been Disassembled for Computation - Percent Utilization of Phosphorus and Nitrogen on Earth by Living Things

A 2015 paper by Landenmark et al estimates the total number of DNA bases in nature as 5.3x10^31 megabases. This of course leads to questions like: how much of the elements on Earth is life on Earth using? I'm aiming for an answer within an order of magnitude. This has implications for concerns about AI takeoff that I will return to at the end.


NITROGEN

Living things occupy slightly more than a billionth of the planet's nitrogen in our DNA (0.000000115%). Living things occupy 0.0023% of the planet's nitrogen overall, the lion's share of which of course is in protein. (See my assumptions below if you like.)


PHOSPHORUS

Living things are using only 0.00047% of the planet's phosphorus in our DNA - but that expands to 4.7% of the planet's phosphorus in living cells overall. This is a much more significant fraction.


Does this difference exist because life on Earth has chosen phosphorus as, effectively, energy currency to manipulate gradients? Or because nitrogen is harder to make biologically available? Even now we rely on relatively few bottlenecks to fix it.



IMPLICATIONS FOR AI TAKEOFF

There's no reason to assume that these numbers represent a global, rather than local optimum for resource utilization for replicators on Earth. That said, we've had four billion years to optimize. This is relevant because of the concern that AI taking off without regard to human welfare would disassemble the Earth into atoms for computation - the farther we are from truly optimized resource utilization, the more an intelligence explosion would be disruptive to the status quo. I found the Bar-On paper on amount of DNA in the biosphere from a link in a discussion about the computational efficiency of nucleic acids in cells. The latter paper suggests that protein translation is several orders of magnitude faster than the fastest current computers, and only an order of magnitude under the Laundauer limit. Of course, resource utilization and computing speed are two different variables, but it seems computation is getting near optimized already - and yet, no disassembly of the Earth for phosphorus. Not even 5% of the energy currency atoms are put to work! Of course, an AI would be qualitatively and quantitatively different in unpredictable ways from what came before, in which case there is no point in discussing this - but the replicators that exist in reality make the best starting point for such a discussiong.

What's more, protein translation is computation in the service of replication. It is quite likely that AIs would end up being selected in much the same way as cells have, with limited resources to be dedicated to refining the model of the universe (getting smarter.) The ivory tower AI super-minds would be dominated by the silicon bacteria. Of course, this is still no reason to think a hard AI takeoff could be disastrous for all life on Earth, an extinction like we've never seen - which the AIs themselves might not have the foresight to survive - but if they do, the best bet is that they will "revert to the mean" of all replicators, with making copies as the goal.




An imperfect analogy. In nature, you have to make do with what's there. The shapes aren't friendly for efficient packing and there are a lot more holes.

Assumptions:

I could not find estimates of the overall mass of nitrogen and phosphorus in the biosphere, so I used the percentage weights in living cells, and derived from a paper estimating the mass of carbon in the biosphere at 5.5x10^14 kg (Bar-On et al 2018), along with carbon being 18% of the atoms in living things.

For both I used 2884.6 kg/m^3 mass of the Earth's crust (weighted the differently dense continental and oceanic crusts at 0.3 and 0.7 resp.) My number for nitrogen comes from nitrogen in the atmosphere, plus nitrogen in the top meter of the Earth's crust, estimating mass of the atmosphere as 5.15*10^18 kg, of which 78.09% is nitrogen, and abundance in the crust as 0.002% by mass (there was some conflict over this between sources actually of up to an order of magnitude; but there is so little nitrogen in the crust compared to the atmosphere, about 347,000 times less using this number, that it's still a rounding error. I assume that there are an equal number of A T C and G which means 3.75xnitrogen atoms per base.

For phosphorus, I used a crustal abundance of 0.1% mass, ignoring the negligible phosphorus in the atmosphere. There is 1xphosphorus atom per base. The major "slop" in this figure occurs because different organisms have different fractions of phosphorus, for one thing since phosphorus is used in structural molecules like bone (85% of phosphorus in humans is in bone; even the same organism at different ages differs substantially, e.g. 0.5% in infants, close to 1% in adults.) Bacteria come in at 0.9% (3% dry weight, assuming 70% water mass per cell) so I used that figure, since bacteria outweigh us by a factor of a thousand, and the number is intermediate even for the values for vertebrates.


REFERENCES

Bar-On YM, Phillips R, Milo R. The biomass distribution on Earth. PNAS June 19, 2018 115 (25) 6506-6511.

P. Kempes CP, Wolpert D, Cohen Z, Pérez-Mercader J. The thermodynamic efficiency of computations made in cells across the range of life. Philos Trans A Math Phys Eng Sci. 2017 Dec 28; 375(2109): 20160343.

Landenmark HKE, Forgan DH, Cockell CS. An Estimate of the Total DNA in the Biosphere. PLoS Biol. 2015 Jun; 13(6): e1002168. Published online 2015 Jun 11. doi: 10.1371/journal.pbio.1002168

Michael Schirber. Chemistry of Life: The Human Body. Livescience.com. https://www.livescience.com/3505-chemistry-life-human-body.html#:~:text=Oxygen%20(65%25)%20and%20hydrogen,%25)%20is%20synonymous%20with%20life.

New Estimate for Number of Active Civilizations in the Milky Way

A summary:

• At a lower bound, it's estimated on average there is one 17,000 LY away. The number that is being reported is that this means at least 36 civilizations in the galaxy.
  
  
• They mention the problem of relying on M-class stars as abodes for life - because they're quite unstable (flares). I have not read the paper in detail, but it seems hard to understand, if there are only 36 star systems, why those couldn't all be G-class stars.
  
  
• They also estimate a lower bound of communicating for only a century (since we've been communicating for that long so we know it's possible.) If it's only a 100 year period, if we're hearing them now, they were active before agriculture.
  
  
• There's also the problem of being able to discern signal from noise at that distance - and not knowing what type of signal we're looking for. A useful thought experiment is the C-index, which is the distance at which we could detect a twin Earth with identical EM emissions. By most estimates, even if there were a twin Earth orbiting Alpha Centauri, we still today could not hear them. This leads the authors to conclude that interstellar communication is for all intents and purposes impossible.
  
  
• Therefore, any persisting civilization is plausibly more likely to be detected by self-replicating artifacts. This all reinforces the greater relative importance of looking for artifacts in our own solar system, which is something we can conceivably do with known technology in the near future, with less of a signal-to-noise problem.
  

Westby T. and Conselice CJ. The Astrobiological Copernican Weak and Strong Limits for Intelligent Life. The Astrophysical Journal. 2020 June 15.

The Asimov Library, and the Idea Catalog

Hat tip Marginal Revolution for both of these.

1. the nucleus of it is starting with this man, who as a labor of love is collecting/cataloging all of Asimov's work. Thank you Steven Cooper!
   
   
2. Catalog of science fiction ideas by year appearing - I've linked to the nineteenth century.

Review: Ad Astra

Initially I was excited to see this, not sure why it got so little fanfare, and now I know. Critics were surprisingly positive. I notice that any time Brad Pitt is in something, they give the film as a whole an inflated grade, even if he turns in consistently good performances. I can see why critics get a warm glow from his projects - he's a good actor, he's good-looking, he's a nice guy and he takes his profession seriously. But that can't save everything, and a movie with him, Donald Sutherland and Tommy Lee Jones that isn't a home run strongly suggests there's a problem with the script.

And there is. This is a movie that can't make up its mind. Are we a near-future hopeful thriller, or a nostalgia film, or a dark reflection on the qualitative differences of the new frontier and whether humans are up to the challenge. (It is possible to be all three, but this film ended up with a few confused moments of each and executed on none of these themes.) Do we want to be a plot coupon-collecting adventure, or a psychological exploration? (It's hard to tell which was central in the writers' minds, and which was added to support the other, because both are so unsatisfying.) The reasons many scenes take place are thin and barely coherent.

Keep in mind SPOILER ALERT I only watched to the part where he contacts his father from Mars, and read about the rest of it online to avoid investing another hour of my life in it.

1. The most realistic portrayal of space travel in film? That's a serious assertion made by the creators of this? 73 days to Neptune and a week or so to Mars...come on. Very little in the way of considering automation. It seems like they took the aesthetic of the Apollo era and extended it to the late 21st century, except the rockets were magically faster.
   
   
2. Action sequences are overall, again, crow-barred in as well, to keep it interesting. The only one that seemed interesting was the fall from the exploding antenna at the beginning. Reminds you of the drop onto Vulcan in the first Star Trek reboot-meets-Baumgartner and Kittinger.
   
   
3. The journey across the Moon is where it really started to lose me. Why again do they not just land there initially, or failing that, at least take a rocket? Oh yeah, the Moon pirates. Surviving on the Moon takes a massive amount of infrastructure. So where are these Moon pirates hiding out that they're undetected, and how do their supplies get to them without detection? Within minutes of their appearance they're wiped out from over-the-horizon artillery, so it's hard to explain how a major operation like a Moon-base could get very far. Apparently it took a human seeing them to detect them (and not a satellite - ???) It's this and many other things that make the movie just seem like a cobbled-together set of action sequences with very little thought. We have almost zero background on the world situation at the time, which is made most obvious by these events (if the Moon is a war zone, who's at war? Over what?)
   
   
4. Why does a biomedical station have to be in interplanetary space between Earth and Mars? What do they get out there that they can't get in Earth orbit? This is where the movie more or less lost me.
   
   
5. Why again do they have to go to Mars to transmit to Neptune? And at closest, the one-way light speed communication time is four hours. Even if there is some hint I missed that in fact he's sitting there for hours, this is not conveyed well.
   
   
6. The "psychological" aspect to the movie - the father-son relationship, the protagonist's personality structure - is so trite and ham-fisted and again feels so crow-barred in that it's simultaneously irritating to have to sit through, and annoying at how ineffective it is. I thought the psych evals were going to be a clever plot twist and Pitt's character was fooling them.
   
   
7. Antimatter flares heading toward Earth and destroying all life? Even if this were the most realistic depiction of space travel, the liberties taken with other aspects of science dominate. It's a poor man's Interstellar, right down to its less effective attempts to carry on in the tradition of 2001.
   
   
8. The philosophical implications of being the only, or the first intelligence - unless there's something really subtle that the summaries missed, this movie really missed an exploration of a theme that's under-explored in science fiction in general and especially in movies.