Every time I mention a Brian Aldiss novel, I have to be careful to check the original title against the one published in the US. The terrific novel Non-Stop (1958) became Starship in the States, rather reducing the suspense of decoding its strange setting. Hothouse (1962) became The Long Afternoon of Earth when abridged in the US following serialization in The Magazine of Fantasy & Science Fiction. I much prefer the poetic US title with its air of brooding fin de siècle decline as Aldiss imagines our deep, deep future.
Imagine an Earth orbiting a Sun far hotter than it is today, a world where our planet is now tidally locked to that Sun, which Aldiss describes as “paralyzing half the heaven.” The planet is choked with vegetation so dense and rapidly evolving that humans are on the edge of extinction, living within a continent-spanning tree. The memory of reading all this always stays with me when I think about distant futures, which by most accounts involve an ever-hotter Sun and the eventual collapse of our biosphere.
Image: The dust jacket of the first edition of Brian Aldiss’ novel Hothouse.
Indeed, warming over the next billion years will inevitably affect the carbon-silicate cycle. Its regulation of atmospheric carbon dioxide is a process that takes CO2 all the way from rainfall through ocean sediments, their subduction into the mantle and the eventual return of CO2 to the atmosphere by means of volcanism. Scientists have thought that the warming Sun will cause CO2 to be drawn out of the atmosphere at rates sufficient to starve out land plants, spelling an end to habitability. That long afternoon of Earth, though, may be longer than we have hitherto assumed.
A new study now questions not only whether CO2 starvation is the greatest threat but also manages to extend the lifetime of a habitable Earth far beyond the generally cited one billion years. The scientists involved apply ‘global mean models,’ which help to analyze how vegetation affects the carbon cycle. Lead author Robert Graham (University of Chicago), working with colleagues at Israel’s Weizmann Institute of Science, is attempting to better understand the mechanisms of plant extinction. Their new constraints on silicate weathering push the conclusion that the terrestrial biosphere will eventually succumb to temperatures near runaway greenhouse conditions. The biosphere dies from simple overheating rather than CO2 starvation.
The implications are intriguing and offer fodder for a new generation of science fiction writers working far-future themes. For in the authors’ models, the lifespan of our biosphere may be almost twice as long as has been previously expected. Decreases in plant productivity act to slow and eventually (if only temporarily) reverse the future decrease in CO2 as the Sun continues to brighten.
Here’s the crux of the matter: Rocks undergo weathering as CO2 laden rainwater carrying carbonic acid reacts with silicate minerals, part of the complicated process of sequestering CO2 in the oceans. The authors’ models show that if this process of silicate weathering is only weakly dependent on temperature – so that even large temperature changes have comparatively little effect – or strongly CO2 dependent, then “…progressive decreases in plant productivity can slow, halt, and even temporarily reverse the expected future decrease in CO2 as insolation continues to increase.”
From the paper:
Although this compromises the ability of the silicate weathering feedback to slow the warming of the Earth induced by higher insolation, it can also delay or prevent CO2 starvation of land plants, allowing the continued existence of a complex land biosphere until the surface temperature becomes too hot. In this regime, contrary to previous results, expected future decreases in CO2 outgassing and increases in land area would result in longer lifespans for the biosphere by delaying the point when land plants overheat.
How much heat can plants take? The paper cites a grass called Dichanthelium lanuginosum that grows in geothermal settings (with the aid of a symbiotic relationship with a fungus) as holding the record for survival, at temperatures as high as 338 K. The authors take this as the upper temperature limit for plants, adding this:
Importantly, with a revised thermotolerance limit for vascular land plants of 338 K, these results imply that the biotic feedback on weathering may allow complex land life to persist up to the moist or runaway greenhouse transition on Earth (and potentially Earth-like exoplanets). (Italics mine)
The long afternoon of Earth indeed. The authors point out that the adaptation of land plants (Aldiss’ continent-spanning tree, for example) could push their extinction to even later dates, limited perhaps by the eventual loss of Earth’s oceans.
…an important implication of our work is that the factors controlling Earth’s transitions into exotic hot climate states could be a primary control on the lifespan of the complex biosphere, motivating further study of the moist and runaway greenhouse transitions with 3D models. Generalizing to exoplanets, this suggests that the inner edge of the “complex life habitable zone” may be coterminous with the inner edge of the classical circumstellar habitable zone, with relevance for where exoplanet astronomers might expect to find plant biosignatures like the “vegetation red edge” (Seager et al. 2005).
The paper is Graham, Halevy & Abbot, “Substantial extension of the lifetime of the terrestrial biosphere,” accepted at Planetary Science Journal (preprint).
Hothouse is an excellent novel. Obviously quite dated now, but still a good read
Yes, as are so many of the Aldiss novels of that period. Well worth re-reading.
For far-future novels, I’m partial to “Dark is the Sun” by Philip José Farmer, myself :)
Thanks for the tip! I haven’t read that one.
How is a story set 3 billion years in the future dated? :^)
https://brianaldiss.co.uk/writing/novels/novels-h-l/hothouse/
At 338 K (65 C), mammals will no longer be part of the biosphere unless there are refuges where the temperature is much lower. The Eocene Thermal Maximum was about 6C greater than today, and even the Permian extinction had estimated average surface temperatures of up to 25 C. Any animals will have to adapt to this extreme heating, probably retreating to the poles, underground, and in the deep ocean.
But we should disabuse ourselves of the vision of complex life on the surface, like the dense tropical vegetation in “Hothouse”. We know extremophiles can survive in temperatures of up to 121 C. The temperatures below ground are far more stable and likely protective. This suggests microorganisms, probably bacterial or archaeal, will be the last type of life on Earth.
If Earth was to become tidally locked, that would be a saving grace, as it would allow for temperate conditions along the terminator. The problem is the transition from current day-night cycles to reach that point. Mobile animals like fish might migrate to maintain their temperatures, but this is not an option for land-living animals, plants, and relatively immobile animals.
Cixin Liu’s “Wandering Earth” nooks seem like the better path if we could manage it. Move the Earth outwards to maintain an equitable temperature, slowly enough to allow for annual reproduction rates to evolve with the longer years, or perhaps engage in “star lifting” to remove mass from the sun to offset its heating. One can only hope our descendants have the technology to ensure that our terrestrial life is not lost and can be spread to other star systems that are currently sterile.
Even if humans last another million years, this is an eyeblink in the deep time being envisaged. Surely within that time, we will have come up with solutions for protecting our biosphere, from sunshades to more drastic approaches as the sun becomes a red giant billions of years in the future.
If we are to become gods, we really should learn to act beneficently towards our home world.
@Tolley. Earth husbandry versus resource exploitation; a lot has to change.
While moving the Earth to a higher orbit sounds fine (given enough energy), it would require life to evolve to deal with longer years. Mars has years about 2x as long as Earth’s, but most Earth life is attuned to 12-month reproduction cycles to coincide with [seasonal] food production. A higher orbit would play havoc with much Earth-life, especially if it could not evolve to the longer annual period length.
IMO, the easier approach is sunshades, either orbital or floating in the stratosphere. I would think that this method would nicely control surface insolation to maintain the ideal temperatures. Floating platforms may even be useful to control the weather and manage rainfall to better distribute it and avoid floods. I imagine the platforms using solar PV or wind turbines to generate the lifting gas, manage to stationkeeping, and dynamically control the insolation. The downside is that these platforms need to be maintained, whilst other approaches like moving the planet may not.
More than the terminator – the day side as a whole could be pretty habitable from what I’ve read, and cloud formation and the high temperature differential between the day and night side makes them more resilient to runaway greenhouse warming.
On the time-frame of millions of years, we could just outright move Earth to a higher orbit – although I suspect they’d just use sunshades if Earth is still intact as a planet.
“I suspect they’d just use sunshades if Earth is still intact as a planet.” People are talking about that now to reduce global warming or in the near future to make Mars (or Venus) habitable. Also in the future, we can control the CO2 cycle by burning fossil fuels and/or limestone to keep Earth habitable.
Star lifting is an idea I’ve always been partial to. It’d not only keep the Sun at a comfortable temperature but also prolong its lifespan. The technology required would be awe-inspiring in scale, but that’s always the case when talking about the distant future…
Surely, it is highly unlikely that humans will be around in 1 billion years in their current anatomical form?
@spaceman
1 million years is a reasonable lifetime for a species. IOW, our form under Darwinian selection would stay fairly similar. Unnatural selection through technology is a different matter. IMO, our technology will determine our descendants, whether biological or artificial.
I said 1 billion years, not 1 million. Do you think humans will remain in their current anatomical form on Earth in 1 billion years?
There has not been 1 bn years for any complex species to remain unchanged to date, simply because most phyla emerged less than 1 bn years ago. For most animals, even 10 million years is extreme longevity as a species. In 1 bn years there may be extinctions of whole genera, let alone species., and species will evolve.
So I think we can say with certainty, that without technological intervention, humans in our present form will no longer exist. But note that technological intervention. Gene banks could preserve our species’ form and be used to maintain it over vast periods of time, simply by reproducing new people with old genomes. Whether we do that, or a culture decides to do that, is unknown.
If we become a space-faring species, and if we do colonize other star systems, or even just build a vast number of Earthlike habitats, there is great room for each culture to decide how to live, from extreme prevention of evolution to preserve form, to electronic transcendence.
Humans can break the rules of the natural world opening up a great number of possible futures.
Or we might wreck our civilization entirely, with natural selection taking back precedence and our species entirely disappearing in time.
It is interesting that the dense vegetation, usually in tropical jungles, is the setting for “the unknown”. Aldiss had uncontrolled vines invading the corridors of the starship in “Non-Stop”. He revisited a tropical world in “Helliconia Summer”.
4 posts ago, the intro included Burroughs’ Mars (Barsoom) stories. Mars was depicted as a drying world much like Lowell’s speculations. But Burroughs’ other famous stories were his Tarzan stories set in the African jungle, a place where there could be undiscovered people and wonders just over the hill.
I suspect our East African Plains Ape ancestry is responsible for this viewpoint. Unlike our ape cousins, we left the dense forests to live on the Savannahs. The greater distances we could see are reflected in our preferred landscapes and landscape paintings. Conversely, the forests are places of fear, where bad things happen. We admonished our children to stay away from the forests with tales like “Red Riding Hood” and “Hansel and Gretel”. Movies like “The Cabin in the Woods” and of course, the Jurassic Park franchise emphasize the darkness of the forest and the dangers hiding nearby.
The contemporary Amazon basin in Brazil, as well as the jungles of Mexico, once almost impenetrable mysteries away from the rivers, are now revealing their secrets as LIDAR reveals structures beneath the tree canopy. Our distance vision is restored with different wavelengths, as well as our ability to fly and orbit over the Earth.
It is ironic that we are now pushing for greater reforestation to try to ameliorate rising CO2 levels. The new fashion for building engineered wood high rises to consume new forest growth and store carbon in wood is a related part of that response.
Yes, I thought about that Non-Stop connection and almost mentioned it. You clearly know your Aldiss, Alex!
Exploring deep time is something that may save science fiction. I’m interested in exploring where the genre can take us when so many themes have been shut off or moved into the realm of fantasy?
Themes closed off:
time travel is likely impossible (we haven’t been visited),
interstellar transportation of life is impossible (also, we haven’t been visited),
mind reading, teleportation, and other psychic abilities are impossible (never demonstrated credibly) and
various kinds of super powers are impossible (by correct understanding of physics and biology).
Where does the genre go from here. I’m nostalgic for “Starman Jones”, Heinlein, 1953.
I’ve had two separate conversations about Starman Jones in the past month with people who are likewise nostalgic. I absolutely loved that one and have re-read it a number of times since.
Well it’s farfetched, but perhaps we have been visited by time travelers!
And it could even be the answer to the fermi-paradox.
So for example:
——–
This may not be the original timeline–maybe they took out an even worse past tyrrant (than in our current time line) and it collapsed into this new timeline considered magnitudes better/safer in comparison.
——–
Or in another crazy example:
maybe some rogish time travelers did actually show up when Stephen Hawking invited them to a party on a specific date. And the world was shocked and amazed.
And we were here on this forum, you and I, all freaking out and discussing it!
But the proverbial time police were not so pleased, and then went back and countered or erased the rogue travelers…
And our timeline reset back to “normal”, our previous discussions about it here–gone and forgotten.
And Stephen Hawking was like: “You see! No time travelers!”
——–
Finally:
If backwards time travel is say far “easier” than we suspect…
Then that would perfectly explain the fermi paradox:
Perhaps thousands of galactic civilizations have arisen and flourished but then keep deleting themselces from history.
Essentially, nobody can resist the temptations of time travel–if only just for the mega jackpot winning numbers.
Or, if only just to save a loved one from an accident.
Or far darker: if only just to vanquish enemies and apposing political groups…
Etc… Etc… Until the ever continuously altered timeline becomes so increasingly degraded–constantly eroding–the civilization first vanishes as a galactic empire, then vanishes all together.
Though I agree that it is easy to get disillusioned about how some of these exotic possibilities have not been realized, I do not think we can count out:
*Interstellar transportation of life
*Time travel into the future
Nor can we say that interstellar transportation of life is impossible because we have not been visited. It could be that life is rare to begin with or that complex life and intelligence are rare even though simple life is common.
That said, I love the theme of “deep time”– especially deep time into the future. Think of all of the strange and interesting creatures that will evolve between now and when Earth’s habitability window closes!
In the mid to late 1990s, I attended the Contact conventions in the Bay Area and participated in the Coti Mundi project, which over several years was one of the most complete exosolar world building projects ever done rivaling James Cameron’s Avatar.
https://contact-conference.org/archive/epona.html
https://contact-conference.org/archive/coti.html
As part of the set up, it was postulated that Epona spent most of its time in a cold, CO2 depleted state, except for brief periods when intense flood basalt eruptions raised both CO2 levels and the temperature. Our model was set during one of these times.
I, however, applied myself to looking at what sort of vegetation would occur in the intervening low CO2 times.
Some of the ideas I came up with were:
Substitution of Nitrogen for Carbon, I.e. proteins for cellulose.
Silicate skeletons
Changes in morphology
The direct extraction of carbon for carbonate in the rock.
Grasses have already started down this path. They already incorporate silica (to make them less edible.) And bamboo has gone from the solid pillar to hollow tube arrangement, which uses considerably less cellulose. An open truss arrangement like a radio tower would be even more efficient. They also use the C4 carbon pathway, which compared to the older C3 pathway, more efficiently fixes Carbon.
However, the future evolution of plants on Earth is pretty moot as there are order of magnitude improvements you can make in both photosynthesis and carbon fixation, and genetic engineers are already working on these. So, the Earth will be covered in these super-plants and their descendants.
Firstly, it needs to be stressed that what the authors are saying is that the LAND biosphere collapses, not the total planetary biosphere. They make the assumption that land vascular plants cannot survive at the temperature of 338 K, and therefore the energy fixation of the land biosphere fails that in turn eliminates the whole food chain. This may be an unwarranted assumption.
Firstly, this says nothing about the marine biosphere that will still have complex plants such as macroalgae that will still photosynthesize using the vast carbonate reserves of the ocean and the cooler temperatures of the ocean. Marine algae, still the most prolific photosynthesizers will still survive. They will provide the base of the marine food chain.
Secondly, marine animals are not exclusively confined to the ocean. Many species, especially the invertebrates, do emerge onto the land, if mostly the shorelines. The biosphere may then look like the period before plants and animals emerged to live on the land.
While the global temperature may be high, we can expect it to be cooler towards the poles. The Antarctic continent may emerge as a refuge for land plants, and continental drift may result in continents spanning the north pole too, allowing a second refuge.
Land plants may not survive the temperatures, but what about fungi? As long as marine algae continue to photosynthesize, aerobic life can continue to evolve forms to survive higher temperatures and live on the land, even if land-based primary productivity through photosynthesis is absent. Carbon fixation by anaerobes could still exist on land and therefore provide a food source for animals and saprophytes.
IOW, the land will not become sterile until the temperatures everywhere on the Earth exceed that of all life forms. I doubt that complete sterilization could occur until the greenhouse was in full swing, boiling away the oceans and even heating the crust to beyond-survivable temperatures.
Even at that point, Earth might support aerial life, as speculated about in the Venusian atmosphere. The surface temperature falls with altitude and therefore any plants that have evolved to float in the atmosphere using gas bladders could still photosynthesize and spread, perhaps falling to the surface and providing food as litter for surface-dwelling animals. Flying animals, such as insects could live at altitude around these aerial plants. I can imagine such plants dropping briefly to the surface to acquire nutrients, especially phosphorus and trace elements while extracting nitrogen and sulfur from gases in the atmosphere.
Perhaps this vision of a billion or two years hence is not so far removed from “Hothouse”?
Unlike the speculative microbes in the Venusian atmosphere, or the huge floating organisms in Jupiter’s atmosphere in Clarke’s “A Meeting With Medusa”, my speculative floating plants need not evolve by natural selection, but rather by our descendants’ intelligent design. Terrestrial algae like bladderwrack might be a base from which to design a form with huge bladders filled with hydrogen (split from water but not combined to fix carbon) to keep the plant afloat in the atmosphere where it can photosynthesize in the cooler stratosphere. It would need a cuticle like cacti to prevent dessication, and some mechanism to allow it to change altitude, perhaps “daggers” of air or water like the old, pre-WWII airships. Reproduction might be wind or insect mediated, with perhaps the offspring attached to the parent until it had developed the structures to be able to float itself as a free-living plant.
Such a designed floating ecosystem might be humanity’s descendants’ last gift to Gaia.
Exploring The Potential Of Plant Astrobiology: Adapting Flora For Extraterrestrial Habitats: A Review
By Keith Cowing
Status Report
Biol Futur via PubMed
September 21, 2024
In recent years, the realm of astrobiology has expanded beyond the search for microbial life to encompass the intriguing possibility of plant life beyond our planet.
Plant astrobiology delves into the adaptations and mechanisms that might allow Earth’s flora to flourish in the harsh conditions of outer space and other celestial bodies.
This review aims to shed light on the captivating field of plant astrobiology, its implications, and the challenges and opportunities it presents. Plant astrobiology marries the disciplines of botany and astrobiology, challenging us to envision the growth of plants beyond Earth’s atmosphere.
Researchers in this field are not only exploring the potential for plant life on other planets and moons but also investigating how plants could be harnessed to sustain life during extended space missions.
Full article here:
https://astrobiology.com/2024/09/exploring-the-potential-of-plant-astrobiology-adapting-flora-for-extraterrestrial-habitats-a-review.html?fbclid=IwY2xjawFcAJtleHRuA2FlbQIxMQABHSVhhLfTxhKjG-eXAiA-DI7CTrlW0Nf8wprTShf9fx3f0oTzKsIUBK6xxw_aem_Knt3eWa0hdSGQQwbb0uU-g
Paper here:
https://pubmed.ncbi.nlm.nih.gov/39302628/
Plants will survive us and adapt to much more complex environments through their incredible survival strategies. See the fern that has crossed the millennia; the flora of Chernobyl lush and perfectly healthy only 40 years after such an imbalance, violent and totally artificial. If the plant world has achieved such an exploit, it will have no problem to survive a few million additional years, the time factor will allow it to develop other strategies. Plants are living beings and we are very fragile next to them.
Nb: should we consider Chernobyl as a catastrophe if we admit that the phenomenon of mutation has strengthened species in the long term?
What seems “invasive” on the planet will create other habitats by colonization between species, but these habitats will tend to rebalance themselves …if humans do not touch them.
We talk about temperature increases but at what scale? A few degrees It is more and it is a tremendous increase in biodiversity. Let’s not forget that a plant never lives alone but always in symbiosis with another species (insect; fungus etc) and its environment by photosynthesis.
In my opinion the problem will lie here by the overabundance of light and various radiations due to our future red giant.
Add a few more degrees and we get the extramophyles: the species will become rarer but they will develop extremely robust survival strategies Look at the incredible “principle” of the fruit dehiscent or finally, the DNA of a plant is encapsulated; the species becomes lethargic to survive. I would say that we should look for hazelnuts in asteroids;)
When the earth’s surface will be burned by the heat of our red giant, why not consider that our seed is buried in a rock block and that the whole thing is sent into space, naturally or artificially, so that Life continues elsewhere? Better a little than nothing to start an adventure…
In French, the title of the book is “le monde vert”. I have not yet read it.
An excellent video on very long term human projects…
https://youtu.be/HOpa7w5lQus?si=pplyKfkNFhtDpf9M
https://www.southampton.ac.uk/news/2024/09/human-genome-stored-on-everlasting-memory-crystal-.page
Human genome stored on ‘everlasting’ memory crystal
Published:19 September 2024
University of Southampton scientists have stored the full human genome on a 5D memory crystal – a revolutionary data storage format that can survive for billions of years.
The team hope that the crystal could provide a blueprint to bring humanity back from extinction thousands, millions or even billions of years into the future, should science allow.
The technology could also be used to create an enduring record of the genomes of endangered plant and animal species faced with extinction.
Eternity crystals
The 5D memory crystal was developed by the University of Southampton’s Optoelectronics Research Centre (ORC).
Unlike other data storage formats that degrade over time, 5D memory crystals can store up to 360 terabytes of information (in the largest size) without loss for billions of years, even at high temperatures. It holds the Guinness World Record (awarded in 2014) for the most durable data storage material.
The crystal is equivalent to fused quartz, one of the most chemically and thermally durable materials on Earth. It can withstand the high and low extremes of freezing, fire and temperatures of up to 1000 °C. The crystal can also withstand direct impact force of up to 10 ton per cm2 and is unchanged by long exposure to cosmic radiation.
The team at Southampton, led by Professor Peter Kazansky , use ultra-fast lasers to precisely inscribe data into nanostructured voids orientated within silica – with feature sizes as small as 20 nanometres.
Unlike marking only on the surface of a 2D piece of paper or magnetic tape, this method of encoding uses two optical dimensions and three spatial co-ordinates to write throughout the material – hence the ‘5D’ in its name.
Restoring species
The longevity of the crystals mean they will outlast humans and other species. Currently it’s not possible to synthetically create humans, plants and animals using genetic information alone, but there have been major advances in synthetic biology in recent years, notably the creation of a synthetic bacterium by Dr Craig Venter’s team in 2010.
Memory of Mankind archive in Hallstatt, Austria
“We know from the work of others that genetic material of simple organisms can be synthesised and used in an existing cell to create a viable living specimen in a lab,” says Prof Kazansky.
“The 5D memory crystal opens up possibilities for other researchers to build an everlasting repository of genomic information from which complex organisms like plants and animals might be restored should science in the future allow.”
To test this concept, the team created a 5D memory crystal creating containing the full human genome. For the approximately three billion letters in the genome, each letter was sequenced 150 times to make sure it was in that position. The deep-read sequencing work was done in partnership with Helixwork Technologies .
Visual clues
The crystal is stored in the Memory of Mankind archive – a special time capsule within a salt cave in Hallstatt, Austria.
When designing the crystal, the team considered if the data held within it might be retrieved by an intelligence (species or machine) which comes after us in the distant future. Indeed, it might be found so far into the future that no frame of reference exists.
“The visual key inscribed on the crystal gives the finder knowledge of what data is stored inside and how it could be used,” says Prof Kazansky.
Above the dense planes of data held within, the key shows the universal elements (hydrogen, oxygen, carbon and nitrogen); the four bases of the DNA molecule (adenine, cytosine, guanine and thymine) with their molecular structure; their placement in the double helix structure of DNA; and how genes position into a chromosome, which can then be inserted into a cell.
For a visual indication of which species the 5D memory crystal relates to, the team paid homage to the Pioneer space craft plaques which were launched by NASA on a path to take it beyond the confines of the Solar System.
“We don’t know if memory crystal technology will ever follow these plaques in distance travelled but each disc can be expected with a high degree of confidence to exceed their survival time,” adds Prof Kazansky.
Sounds like a winner.
And hubbout a bit of epigenetics and such pesky items as histones?
I don’t believe any complex organism like a human can be recreated just from DNA. This may apply whatever the technology is available. It will require a human or simulated human to develop a fertilized egg.
However, this technology strikes me as eminently suitable for seed ships, where humans (or artificial wombs)
are available at the destination to gestate a cell with the DNA replaced by that encoded in the storage device. It may need extra information, but it should be possible to recreate human populations this way at distant star systems, even if our starships are slow boats.
As with all such technology, the means to extract the information are required. It would make an excellent archiving technology that could be a hedge for civilization collapse, or an Encyclopedia Galactica for civilizations widely separated in time. Or the storage medium for von Neumann replicators.
Hot Archaean hypothesis states that before oxygenation, global temperatures were 55 – 85 celsius because of intense methane and CO2 greenhouse, meaning that thermophilic adaptation was widespread and necessary. Maybe it even was in the “starting pack”. If future temperatures rise slowly, than thermophilic adaptation might return. Together with development of reflective foliage and other unforeseen adaptations, this might postpone even moist greenhouse onset itself, extending habitability right until the final turn-off from main sequence some 7 billion years from now.
I haven’t heard of this Hot Archaean Hypothesis, but I was under the impression that the “cool young Earth” was a problem due to the less luminous sun and insufficient atmospheric GHGs to warm the planet. Hydrogen might be added to the atmosphere to keep the surface warm enough for liquid water to form.
Clearly, the Earth was very hot during its formation, and oceans did apparently exist about 100 my after formation, but as water was pulled out of the atmosphere leaving N2/CO2 and some CH4, the surface cooled leading to a paradox of insufficient insolation and GHG energy trapping to keep a modeled surface warm enough for liquid water.
That Archaea include thermophiles does not require that the Earth’s average temperature must have been high, but rather that their favored habitat, and possibly their origin, was very hot. These habitats include ocean hot vents and hot springs.
This article, The Archaean Atmosphere (2020), suggests that the Archaean period might have had temperatures ranging from 0 C to 40 C.
Quote from the The Long Afternoon of Earth: ” Rocks undergo weathering as CO2 laden rainwater carrying carbonic acid reacts with silicate minerals, part of the complicated process of sequestering CO2 in the oceans. The authors’ models show that if this process of silicate weathering is only weakly dependent on temperature – so that even large temperature changes have comparatively little effect – or strongly CO2 dependent, then “…progressive decreases in plant productivity can slow, halt, and even temporarily reverse the expected future decrease in CO2 as insolation continues to increase.” This statement is not supported by the principles of atmospheric physics. The whole carbon cycle is based on the Milankovitch cycles which are very fine tuned and affected greatly by only small temperature changes. CO2 starvation always and only occurs on the part of the M cycle when the Earth receives less sunlight and the temperatures are lower on average. The ice ages are CO2 starved. There were no polar ice caps before forty million years ago and not only the two snow ball Earth periods were they any CO2 Starvation, but these were also followed by the hottest periods in history, the hot house periods due to the carbon cycle. The heat of course kills the life first. At some point there will be much more carbon dioxide than oxygen and eventually the complete loss of the oceans which will be boiled off into space due to jeans escape. The complete loss of the atmosphere eventually?
@Geoffrey
IIUC I think you are conflating cause and effect. The Milankovich cycles are purely about the differential warming of the Earth due to its orbit and the current position of the continents. The current level of solar illumination and CO2 partial pressure in the atmosphere has created ice ages over the last million years or so. Biological carbon cycling is far more important in the short term than the geological carbon cycle. You can see this in the annual CO2 levels (shown in the Keeling data) as the northern temperate forests impact the CO2 level with the seasons.
It is the lack of carbon fixation during cold periods that allows the outgassing of CO2 to build up. This may have been the cause of the end of the “Snowball Earth” condition that eventually returned the Earth to an unglaciated state.
In the future that the paper describes, the sun is more luminous. Ice ages no longer occur. The CO2 can no longer be drawn down by carbon fixation to offset the warming as it is too low for even the more efficient C4 photosynthesis to work effectively. This would result in the end of the land-based biological carbon cycle leaving only the slow geological carbon cycle to be operative.
The paper suggests that this simple model is not accurate and that plants can extend the time the land surface is cool enough for the flora and fauna to continue.
As I have commented earlier, I think their model is too limited as marine photosynthesis will continue and maintain this marine biosphere even if it retreats toward the poles (the reverse of the Snowball condition where the retreat is towards the equator). All land organisms have evolved within the last 1/2 bn years. What evolution may be driven by a warming world where current flora can no longer live over the next 1/2 to one billion years that could extend land-based plants and the food chain that depends upon them?
Remember the adage “All models are wrong, but some are useful”. This applies to global climate modeling which is very complex and does not include the impacts of life on the climate [AFAIK].
I stand corrected. The silicate weathering really makes an impact when there is more coastline and the continents are far apart which coincides with cool periods and the super continents with warm periods which is what has happened in Earth past in deep time. This won’t matter in the future since the Sun is getting hotter. There is always the unknown though. Fifty and one hundred million years from now, we could easily move the orbit of Earth and Mars further out and also the rest of the planets. We could never have to leave until the Sun became a white dwarf, so our planet might just end in a dead freeze instead.
This paper gives an excellent and detailed idea of the chemistry and physical properties of Earth during a snowball period and the changes when it comes to an end.
https://www.nature.com/articles/s41467-024-51412-8
Quote by Alex Tolley: “Remember the adage “All models are wrong, but some are useful”. This applies to global climate modeling which is very complex and does not include the impacts of life on the climate [AFAIK].” Where did you get that quote? I don’t think any good scientist would agree with it.
This is not correct. It is in common agreement scientists especially those with a background in atmospheric physics that photosynthesis played a major role in the snow ball Earth periods and even the reduction of atmospheric carbon dioxide over tens of millions of years which lead to the ice ages. Atmospheric physics always takes precedence over models. The carbon dioxide has to be removed from the atmosphere for the temperature to become lower. This is done through the carbon cycle, silicate weathering and photosynthesis. This is why we have the carboniferous period, coal,, oil, etc. The fact that greenhouse gases like carbon dioxide and methane absorb thermal infra red radiation, but all other electromagnetic radiation gamma, x rays, ultra violet, visible light and radio waves.pass through the CH4 and CO2 molecules This is quantum mechanical where the atoms in these molecules bend and stretch and vibrate and rotate when they absorb infra red. This is a model which is not wrong, but precisely describes thermal black body radiation. Kirchhoff’s law.
Geoffrey – you could have simply looked it up.
“All models are wrong, but some are useful” – coined by the statistician, George Box, this aphorism is just as true in economics as it is in statistics.
Source: How to use a wrong model correctly
I agree. I don’t think that quote applies to physics though as quantum field theory is a model and it is not wrong. It could be improved in the future. Statistics and even mathematics can be used to support an idea which is imaginary, but does not represent a physical reality. The statistics and mathematics themselves are true, but can be used to build a model to support an idea which does not represent a physical reality, but is invalidated later which happens all the time in physics and science. Some old ideas are popular due to their emotional or psychological appeal are hung onto but have not been challenged or conformed to first principles.
The danger with the idea of models is that these are mere abstractions which don’t necessarily represent a physical reality.
The idea of model dependent realism where everything is just of theory or model. One can claim there are many models and therefore not remove any ambiguity and therefore the viewpoint of the physics of climate change for example is questionable. This of course is not scientific.
Quantum field theory, the Langranian and Hamiltonian are based on a reservoir of “idealized, massless, coupled harmonic oscillators basically like two steel balls attached or connected by a spring and there are many of these in the reservoir. These describe Kirchhoff’s law of blackbody radiation. For example the carbon dioxide molecule bends and stretches around 12 to 15 microns in the mid infra red. This is because every atom and molecule has a ground state in the quantum electron jumps between zero and one which is equal to the energy of a specific wavelength in the electromagnetic spectrum. This is how spectroscopy works where every atom and molecule absorbs EMR at a different wavelength equal to the energy of space between zero and one which is different for every atom based on the different energy levels in each one. They all have a different amount of electrons in their shells in the table of elements.
In physics it is the first principles which matter which are considered to be mind independent, objective and unchanging. There are the invariances and conservation laws. They don’t care whether anyone believes they work or not. They always work anyway independent of our wills.
https://astrobiology.com/2024/09/optimizing-photosynthetic-light-harvesting-under-stars-simple-and-general-antenna-models.html
Optimizing Photosynthetic Light-harvesting Under Stars: Simple And General Antenna Models
By Keith Cowing
Status Report
via PubMed
September 22, 2024
In the next 10–20 years, several observatories will aim to detect the signatures of oxygenic photosynthesis on exoplanets, though targets must be carefully selected. Most known potentially habitable exo-planets orbit cool M-dwarf stars, which have limited emission in the photosynthetically active region of the spectrum (PAR, 400<𝜆<700 nm) used by Earth’s oxygenic photoautotrophs.
Still, recent experiments have shown that model cyanobacteria, algae, and non-vascular plants grow comfortably under simulated M-dwarf light, though vascular plants struggle. Here, we hypothesize that this is partly due to the different ways they harvest light, reflecting some general rule that determines how photosynthetic antenna structures may evolve under different stars.
We construct a simple thermodynamic model of an oxygenic antenna-reaction centre supercomplex and determine the optimum structure, size and absorption spectrum under light from several star types. For the hotter G (e.g. the Sun) and K-stars, a small modular antenna is optimal and qualitatively resembles the PSII-LHCII supercomplex of higher plants.
For the cooler M-dwarfs, a very large antenna with a steep ’energy funnel’ is required, resembling the cyanobacterial phycobilisome. For the coolest M-dwarfs an upper limit is reached, where increasing antenna size further is subject to steep diminishing returns in photosynthetic output.
We conclude that G- and K-stars could support a range of niches for oxygenic photo-autotrophs, including high-light adapted canopy vegetation that may generate detectable bio-signatures. M-dwarfs may only be able to support low light-adapted organisms that have to invest considerable resources in maintaining a large antenna. This may negatively impact global coverage and therefore detectability.
Optimizing photosynthetic light-harvesting under stars: simple and general antenna models
Photosynth Res. 2024; 162(1): 75–92. Published online 2024 Sep 10. doi: 10.1007/s11120-024-01118-1 via PubMed (open access)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11413096/
I looked at possible ranges of light that different chlorophylls could capture in this CD post: The Purple Hills of Proxima b and the possible color the plants would have around this M_dwarf sun.
The problem with detecting oxygenic photosynthesis is that O2 can be created abiotically by photolysis of water. The combination of O2 and CH4 as a disequilibrium of gases is the classic biosignature, although it is now considered not such a definite biosignature as abiotic mechanisms must be ruled out..
I read the book yesterday and I must say that I was very surprised by its fantastic Tolkien’s look and less SF. It’s almost on the edge of Lovecraft (the meeting with termites in the tunnel under the sea ! ) In terms of astronomy it doesn’t say much except that the earth has stopped spinning and is warmer. Not my favorite Aldiss…
I’m not convinced. It may be true that increasing the temperature of a passive Earth results in decrease of CO2 levels – a purely geological Gaea explained here ( https://ajsonline.org/article/60278 – the Wikipedia article gives a wrong equation where everything turns to orthosilicic acid, but at least they referenced this link). The concern here seems to be that Earth will go too far regulating its temperature and kill off all the plants, by reducing CO2 to 50 ppm. That’s an eighth of what it is now, and a sixth of what it was around when my father was born, so there is objective evidence that life forms, if sufficiently unintelligent, are capable of solving this problem handily. Plants are not helpless in this regard either – they routinely secrete acids from root hairs to displace desirable cations from soil particles. Acidifying carbonates should have a similar effect, but also release bicarbonate in the process, which the plants would absorb and use. Right now, with CO2 always more than adequate, plants probably don’t focus many resources on acquiring it this way, but they could evolve to do so. Under CO2 limiting pressure, limestone outcrops would become more fertile than other soil, fueling plant photosynthesis, and they would crumble over much less than geological time under the assault of deep roots. It might also be argued that the evolution of humans under unstable climate conditions, to dig up and burn carbon, is already one of Earth’s ways of addressing the problem.
In the long term, Earth’s orbit might be stable, or it might migrate. I don’t really understand https://arxiv.org/pdf/1505.01086 but I get the impression that solar wind can push planets outward in their orbits. While this effect may be too small to matter right now, if we have 40,000 kilometers of space habitats surrounding the Earth in a shining ring, the solar wind and light pressure should be communicated to the planet – is it enough? I wonder if there’s even a risk people will get too greedy with their habitats and collectively flush the planet out into space…
Chemosynthetic life might evolve to tolerate increasingly high temperatures. And why not multicellular chemosynthetic life in deep caverns at increasing depths? But I like the idea of gigantic floating plants in the upper atmosphere, living blimps supporting complex ecologies, they develop carapaces and begin to tolerate decreasing atmospheric pressures, evolve lasers for offense, defense and propulsion and eventually live in vacuum, using space dust and solar flares for sustenance, and laser propulsion for interplanetary travel, eventually colonizing other solar systems.