So here we are early in the year 2022 as an advanced form of carbon-based Intelligence most likely on the brink of creating an advanced form of machine-based Intelligence within the next 100 years or so. But also possibly on the brink of a global thermonuclear war for the second time in 60 years with the invasion of the Ukraine by Russia. The last time things were this scary was back in October of 1962 with the Cuban Missile Crises when I was 11 years old. We are also on the brink of ending all forms of complex carbon-based life on the planet by turning the Earth into another Venus. We have already tripped several climate tipping points by generating an atmosphere with 415 ppm of carbon dioxide and we are still increasing that level by 2.3 ppm each year no matter what we pretend to do about it. But the combination of our current reckless carbon output and the positive feedback loops that we have already initiated will not end all forms of complex carbon-based life on the planet for several thousand years. For more on this global planetary disaster in slow motion see Why Do Carbon-Based Intelligences Always Seem to Snuff Themselves Out?, The Deadly Dangerous Dance of Carbon-Based Intelligence and Last Call for Carbon-Based Intelligence on Planet Earth.
And yet still we sit here patiently wondering why we hear nothing from the rest of the galaxy! In my recent posting Is our Very Large Moon Responsible for the Rise of Software to Predominance on the Earth?, I added the possible necessity of having a very large moon for a rocky planet in the habitable zone of a star system to the list of requirements required by the Rare Earth Hypothesis to produce a carbon-based form of Intelligence. The Rare Earth Hypothesis was first presented in the classic Rare Earth (2000) by Peter Ward and Donald Brownlee and maintains that the Earth is a very rare planet with a very rare history that is hard to match. In Is our Very Large Moon Responsible for the Rise of Software to Predominance on the Earth?, I conjectured that the addition of a great deal of angular momentum to a planet-moon system by a freak collision during its early formation, like the one our current Earth-Moon system experienced when an early proto-Earth collided with a Mars-sized planetesimal called Thea, may be one of the necessary elements of the Rare Earth Hypothesis. Such a rare collision may have been required to initiate the "plate tectonics" thermostat of the Earth that could maintain the Earth at a temperature that allowed for the existence of liquid water on its surface for many billions of years. In that posting, I explained that plate tectonics was key to managing the carbon cycle of a rocky planet by recycling the carbon atoms in its upper mantle and crust. Too many carbon atoms in the atmosphere of such a planet in the form of carbon dioxide would cause the planet to overheat and become a Venus-like planet devoid of all life. Too little carbon dioxide in the atmosphere would cause the planet to become a frigid Snowball Earth planet without the vital supply of carbon atoms needed by complex carbon-based life.
But even with plate tectonics, keeping a rocky silicate planet at a habitable temperature seems rather "iffy". Yes, plate tectonics can subduct the carbon atoms that simple forms of life have sucked out of the atmosphere and allow those carbon atoms to be released back into the atmosphere by volcanic activity at subduction zones of a planet. But what if the elimination rate of carbon atoms from the atmosphere is not properly matched by the correct rate of replenishment of carbon atoms to the atmosphere by volcanic activity at plate subduction zones? If it is not properly matched, the planet will be subject to positive feedback loops that drive the planet to become a completely frozen Snowball Earth or to become an overheated Venus with a runaway greenhouse atmosphere. Studies have shown that a small imbalance of carbon intake and subsequent release of just 25% would have caused the Earth to veer off course into a planet that is either too hot or too cold for complex carbon-based life. Currently, we are finding that about 20% of the exoplanets we find are in the hospitable zone of their star where water could be a liquid on the surface of the planet. But such rocky silicate-based planets in the habitable zone of a star may likely be in an unstable equilibrium like a pencil that has momentarily been balanced on its tip that is ready to easily fall down at a moment's notice. This would suggest that many of the rocky silicate-based planets that we now find in the habitable zone of a star system are only temporarily hospitable for complex carbon-based life for geologically brief periods of time and not for the many billions of years required to bring forth a carbon-based form of Intelligence. In Why Do Carbon-Based Intelligences Always Seem to Snuff Themselves Out? I explained that my Null Result Hypothesis for the absence of galactic software might be that it takes many billions of years in the life of a stable planet for the Darwinian processes of inheritance, innovation and natural selection to allow theft and murder to navigate the many necessary twists and turns to bring forth a carbon-based form of Intelligence, and that carbon-based forms of Intelligence were thus unfortunately preprogrammed to snuff themselves out before they could produce a machine-based form of Intelligence because they simply could not turn off the theft and murder that brought them about in time to save themselves from self-extinction.
Is the Long-Term Climatic Stability of Rocky Silicate-Based Planets the Key?
The above analysis leads to the question - is the Earth rare because of its current attributes or is there more to it? If Earth-like planets in the habitable zone of a star seem quite common in our Milky Way Galaxy, why do we not see any evidence of Intelligence out there? To further explore that question, I would like to refer to a recent paper by Professor Toby Tyrrell of the University of Southampton that is available at:
Chance played a role in determining whether Earth stayed habitable
https://www.nature.com/articles/s43247-020-00057-8
Here is a nice YouTube video by Anton Petrov that covers the paper:
How Did Earth Stay Habitable For 4 Billion Years? Science: LUCK
https://www.youtube.com/watch?v=_SZwOpbTJf0
In the above paper, Toby Tyrrell ran computer simulations of 100,000 Earth-like planets 100 times each to see how many of the Earth-like planets could remain habitable for carbon-based life for a period of 3 billion years. Recall that the Earth has now remained hospitable for about 4 billion years and it took a full 4 billion years to produce a carbon-based form of Intelligence that could one day produce a machine-based Intelligence that could then make itself known to the rest of our Milky Way galaxy. In the paper, Toby Tyrrell acknowledges that there were many fortunate feedback loops in the Earth's history at play that kept the Earth habitable for many billions of years, but he also explains that this might just be evidence of the observer selection bias found in the weak anthropic principle. Naturally, as a form of carbon-based Intelligence, we could only find ourselves on a rocky silicate-based planet that had been habitable for many billions of years because that is what it takes to produce a carbon-based form of Intelligence. Nobody is patiently sitting on a rocky silicate-based planet in the habitable zone of a star system with an atmosphere that ran amuck.
The purpose of Toby Tyrrell's computer simulation of 100,000 Earth-like planets was to see if planets in the habitable zone of a star system could maintain a surface temperature that could keep water in a liquid form for 3 billion years.
The computer-simulated 100,000 Earth-like planets were created with random positive and negative feedback loops that controlled the temperature of the planet's surface. Each planet also had a long-term forcing parameter acting on its surface temperature. For example, our Sun is a star on the main sequence that is getting 1% brighter every 100 million years as the amount of helium in the Sun's core increases. Helium is four times denser than hydrogen and as the Sun's core turns hydrogen into helium its density and gravitational pull increases so its fusion rate has to increase to produce a hotter core that can resist the increased gravitational pull of its core. Each planet was also subjected to random perturbations of random strength that could temporarily alter the planet's atmospheric temperature like those from asteroid strikes or periods of enhanced volcanic activity. The key finding from this study can be summed up by Toby Tyrrell as:
Out of a population of 100,000, ~9% of planets (8,710) were successful at least once, but only 1 planet was successful on all 100 occasions. Success rates of individual planets were not limited to 0% or 100% but instead spanned the whole spectrum. Some planets were successful only 1 time in 100, others 2 times, and so on. All degrees of planet success are seen to occur in the simulation. It can be seen, as found in a previous study, that climate stabilisation can arise occasionally out of randomness - a proportion of the planets generated by the random assembly procedure had some propensity for climate regulation.
Toby Tyrrell's computer simulation of 100,000 Earth-like planets found that when 100,000 Earth-like planets were each run through 100 iterations with random, but realistic, values for the model parameters, about 9% of them maintained a habitable temperature for 3 billion years for at least 1 of the 100 runs. Some models had 1 successful run and others had 2 or more successful runs. The astounding finding was that only 1 of the 100,000 models was successful for all 100 runs! This study would suggest that the Earth may not be rare because of its current habitable conditions. Rather, the Earth may be rare because it was able to maintain a habitable surface temperature for about 4 billion years and become a Rare Earth with complex carbon-based life having Intelligence.
Figure 1 – Toby Tyrrell's computer simulation of 100,000 Earth-like planets suggests that the Earth may be a "hole in one planet" proudly sitting on a fireplace mantle.
Figure 2 – Yet, we are finding many other rocky silicate-based planets in the habitable zones of distant stars and wondering why nobody out there is saying "Hello".
Is our Rare Earth Just a Fluke of Good Luck?
The Earth has been habitable for carbon-based life for about 4,000 million years, ever since the Earth cooled down enough to a habitable temperature that allowed for the presence of water in a liquid form. Once the Earth had sufficiently cooled, simple carbon-based life seems to have been inevitable. For more on that see The Bootstrapping Algorithm of Carbon-Based Life. The very first forms of carbon-based life were the Archea and Bacteria which both used a very simple prokaryotic cell architecture.
Figure 3 – The prokaryotic cell architecture of the bacteria and archaea is very simple and designed for rapid replication. Prokaryotic cells do not have a nucleus enclosing their DNA. Eukaryotic cells, on the other hand, store their DNA on chromosomes that are isolated in a cellular nucleus. Eukaryotic cells also have a very complex internal structure with a large number of organelles, or subroutine functions, that compartmentalize the functions of life within the eukaryotic cells such as mitochondria, chloroplasts, Golgi bodies, and the endoplasmic reticulum.
Prokaryotic cells essentially consist of a tough outer cell wall enclosing an inner cell membrane and contain a minimum of internal structure. The cell membrane is composed of phospholipids and proteins. The DNA within prokaryotic cells generally floats freely as a large loop of DNA, and their ribosomes used to help translate mRNA into proteins, float freely within the entire cell as well. The ribosomes in prokaryotic cells are not attached to membranes like they are in eukaryotic cells, which have membranes called the rough endoplasmic reticulum for that purpose. The chief advantage of prokaryotic cells is their simple design and the ability to thrive and rapidly reproduce even in very challenging environments, like little AK-47s that still manage to work in environments where modern tanks will fail. Eukaryotic cells, on the other hand, are found in the bodies of all complex organisms, from single-celled yeasts to you and me, and they divide up cell functions amongst a collection of organelles (functional subroutines), such as mitochondria, chloroplasts, Golgi bodies, and the endoplasmic reticulum.
It then took about another 2,500 million years of habitable climate for the Eukarya to appear which used the much more complicated eukaryotic cell architecture used by all of the "higher" forms of carbon-based life found on the Earth today. This was probably the most difficult step in producing a carbon-based form of life with Intelligence and that is why it took so very long. The arrival of the eukaryotic cell architecture with built-in mitochondrial power supplies on a planet with an atmosphere containing oxygen was necessary to power multicellular "higher" forms of carbon-based life with Intelligence. After all, it requires a full 20 watts of power to run a human Mind and all that it can contemplate and that is a lot of energy. For more on that see The Rise of Complexity in Living Things and Software. All of the "higher" forms of life that we are familiar with are simply made of aggregations of eukaryotic cells. Even the simple yeasts that make our bread, and get us drunk, consist of very complex eukaryotic cells. The troubling thing is that only an expert could tell the difference between a yeast eukaryotic cell and a human eukaryotic cell because they are so similar, while any school child could easily tell the difference between the microscopic images of a prokaryotic bacterial cell and a eukaryotic yeast cell - see Figure 3. The other thing about eukaryotic cells, as opposed to prokaryotic cells, is that eukaryotic cells are HUGE! They are like 15,000 times larger by volume than prokaryotic cells! See Figure 4 for a true-scale comparison of the two.
Figure 4 – Not only are eukaryotic cells much more complicated than prokaryotic cells, they are also HUGE!
Figure 5 – Complex carbon-based multicellular life consisting of large numbers of eukaryotic cells all working together as a single organism did not arise until the Ediacaran Period 635 million years ago.
Complex multicellular life did not arise until just 635 million years ago during the Ediacaran Period. But very complex carbon-based multicellular life did not really take off until the Cambrian Explosion 541 million years ago. The Cambrian Explosion may have been initiated by the advancement of rudimentary forms of vision by certain Cambrian predators. See An IT Perspective of the Cambrian Explosion for more on that.
Figure 6 – Complex carbon-based multicellure life then really took off during the Cambrian Explosion 541 million years ago.
Yet during this brief period of 635 million years, we have recorded at least five mass extinction events that threatened the very existence of carbon-based life on the planet. These mass extinctions are thought to have arisen from astronomical and geological perturbations to the Earth's climate such as asteroid strikes, supernova blasts and flood basalt eruptions. Some have even been caused by carbon-based life itself messing with the Earth's atmosphere like the Huronian Snowball Earth glaciation, which occurred 2,400 to 2,100 million years ago and may have been triggered by the first appearance of abundant oxygen in the atmosphere as a result of carbon-based life first discovering photosynthesis,
Figure 7 – During the history of the Earth there have been many long periods of many millions of years when the entire planet was frozen over into a Snowball Earth.
But by far the worst mass extinction was the Permian-Triassic greenhouse gas mass extinction 252 million years ago that nearly killed off all complex carbon-based life on the planet. A massive flood basalt known as the Siberian Traps covered an area about the size of the continental United States with several thousand feet of basaltic lava, with eruptions that lasted for about one million years. Flood basalts, like the Siberian Traps, are thought to arise when large plumes of hotter than normal mantle material rise from near the mantle-core boundary of the Earth and break to the surface. This causes a huge number of fissures to open over a very large area that then begin to disgorge massive amounts of basaltic lava over a very large region. After the eruptions of basaltic lava began, it took about 100,000 years for the carbon dioxide that bubbled out of the basaltic lava to dramatically raise the level of carbon dioxide in the Earth's atmosphere and initiate the greenhouse gas mass extinction. This led to an Earth with a daily high of 140 oF and purple oceans choked with hydrogen-sulfide-producing bacteria, producing a dingy green sky over an atmosphere tainted with toxic levels of hydrogen sulfide gas and an oxygen level of only about 12%. The Permian-Triassic greenhouse gas mass extinction killed off about 95% of marine species and 70% of land-based species, and dramatically reduced the diversity of the biosphere for about 10 million years. It took a full 100 million years to recover from it.
Figure 8 - Above is a map showing the extent of the Siberian Traps flood basalt. The above area was covered by flows of basaltic lava to a depth of several thousand feet.
Figure 9 - Here is an outcrop of the Siberian Traps formation. Notice the sequence of layers. Each new layer represents a massive outflow of basaltic lava that brought greenhouse gases to the surface.
For a deep-dive into the Permian-Triassic mass extinction, see Professor Benjamin Burger's excellent YouTube at:
The Permian-Triassic Boundary - The Rocks of Utah
https://www.youtube.com/watch?v=uDH05Pgpel4&list=PL9o6KRlci4eD0xeEgcIUKjoCYUgOvtpSo&t=1s
The above video is just over an hour in length, and it shows Professor Burger collecting rock samples at the Permian-Triassic Boundary in Utah and then performing lithological analyses of them in the field. He then brings the samples to his lab for extensive geochemical analysis. This YouTube provides a rare opportunity for nonprofessionals to see how actual geological fieldwork and research are performed. You can also view a pre-print of the scientific paper that he has submitted to the journal Global and Planetary Change at:
What caused Earth’s largest mass extinction event?
New evidence from the Permian-Triassic boundary in northeastern Utah
https://eartharxiv.org/khd9y
From the above, we can see that keeping a rocky silicate-based planet habitable for billions of years is not an easy thing to do. For example, we can easily imagine that if one of the five mass extinctions that occurred during the past 635 million years had been a little more intense, complex carbon-based life on the Earth could have been easily extinguished. Perhaps the solution to Fermi's Paradox and the reason we see no other galactic software in the Milky Way is that our planet is indeed a Rare Earth after all, and on those very rare planets where complex carbon-based Intelligence does arise, it always seems to snuff itself out with technology before producing a machine-based Intelligence that could make itself known to the rest of the galaxy. If so, this is a critical thing for us all to know and always keep in mind.
Comments are welcome at scj333@sbcglobal.net
To see all posts on softwarephysics in reverse order go to:
https://softwarephysics.blogspot.com/
Regards,
Steve Johnston
