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Dionysus, 1.5 billion years after formation, 80 degrees north[1]. A radiokont fights off a roving Nannopraetorion in the foreground, while a much larger placotestan floats by behind it, unbothered by the attention of the roaming single celled predator.

To the casual observer, there has been no greater milestone in the history of life on Earth than the dawn of multicellular life. While the vast majority of Earth genetic diversity lies in its unicellular inhabitants, as well as the greater portion of its biomass, it’s the three clades of life to have achieved multicellular, macroscale sizes that dominate surface ecosystems. 1.5 billion years after formation, life on Dionysus achieves this milestone.

For many millions of years beforehand, the ecosystem of Dionysus was stuck in a series of wild swings. The first predatory genus, Nannopraetorion, developed out of a group of scavengers adapted to consume portions of dead cells, and rapidly ravaged the young, naive ecosystem, reducing the populations of passive chemosynthetic organisms that were relying on the constant rain of complex organics from the upper atmosphere. This was not a very potent source of energy, and so the local producers were simply wiped out by the predators, unable to reproduce quickly enough in the face of a supercharged, heterotrophic lifeform. These cycles of boom and bust continued for millions of years.

Recently, however, a new form of producer has evolved. Developing from a antecessor that lived in the very uppermost layers of the global ocean, for which they developed anthocyanin-like blue pigments for protection against UV rays, this group started to use these pigments to split water into hydrogen and oxygen. Initially this hydrogen was used to break down long chain and resistant organic compounds in a vastly more efficient manner, but it didn’t take long before a group of these started using the hydrogen to create simple sugars, though unlike sugars on Earth, these were based on 5 carbon furan rings. Now able to access a much more potent source of energy, these organisms were able to compete with Nannopraetorion. 

For a time, anyway. Even though the ecosystems had stabilized, the mortality rate on these early photosynthesizers was very high, creating a strong evolutionary pressure to develop further defenses against their predators. At the same time, rising oxygen levels provided both an additional threat, and an opportunity. 

Oxygen is a toxin to all life, even modern organisms on Earth. It is highly reactive and liable to break apart many chemical bonds, but that also makes it an extremely potent source of energy for those that can harness it. By a freak mutation, some of the early photosynthesizer cells didn’t fully separate when they split, but this helped both cells by reducing their surface area to volume ratio, bringing down the concentration of oxygen in the cells.

This initial, monumental achievement was rapidly developed, and within a million years a new clade had formed, the Protokonta. Protokonts are defined by having distinct “mother cells”, individual cells that are the only ones allowed to divide to grow the colony, which use chemical signals to inhibit division in other cells. At the opposite end of the group of cells, once sufficient size is achieved, a new mother cell develops, an event which triggers division of the entire colony.

The protokontan body plan was wildly successful, and so the clade would almost immediately split into two subgroups, the Radiokonts and the Placotestans. Placotestans have already radically altered themselves externally, growing two shells of xylan, a polymer made up of 5 carbon sugars. These tests are secreted in a ring around the middle of the colony by specialist cells, and once the colony reaches a set size, each cell detaches from the rest, ready to creat a new colony. 

Radiokonta is the more conservative group externally, as the only visible innovation is a series of radial spines that gives the group its name, but this hides the fact that radiokonts have developed significantly more extensive cell-to-cell communication methods, allowing them to link of the contractile elements of their cytoskeletons to coordinate their movements. This allows radiokonts to warp the shape of the colony in the face of danger, bringing their spines together to form an impenetrable defense. Their spines are derived from the same biopolymers as the placotestans, but each cell other than the mother cells excretes a spine upwards.

The Protokonts are still in the middle of their diversification at this point in the history of Dionysus, and indeed in very recent times a new clade of Radiokonta has emerged which is starting to lose its only newly acquired photosynthetic abilities, in favour of more predatory methods…

[1] I'm going to shamelessly steal the coordinate systems used by The Isla Project for all of my tidally locked planets, as that simple makes more sense when the temperature differences are concentric, rather than latitudinal. To be clear, this means that this scene takes place close to the sub stellar point of Dionysus.

Also, please subscribe to them if you haven't already, it's one of the best spec evo projects I've seen!

[minimumsky5]

I knew some bird tracheae went down onto one side of their sternal keel to do this, but not that some also just coiled below their skin like that, or to that extent!

pictures sourced from here, which i will fully admit i clicked on because i saw the words "sauropod vertebra picture of the week" and was so fascinated by this niche that of course i had to check it out,

but apparently a lot of birds have excessively long tracheae that just like.... coils around the top of the lungs?

WHY????????????????????????????????????? (i am now learning that the answer why is that so their calls make them sound Bigger than they actually are)

i feel like so many birds just have uzumaki nightmare shit just like... going on inside of them at all times. like hummingbird & woodpecker skulls!

this is EGREGIOUS. You stop that!!!

[minimumsky5]

Cricetoxenida a suborder of hamster-like aliens,whetever or not this decision is entirely up to you!!!

Given how diverse the forms will be in this system (when I get around to it...), I'm sure we can sneak in that reference! Also, I know it's been a while, but I really, really didn't like how the last picture came out and it kind of demoralised me. I was also trying to make the project less focussed on megafauna and put some microbiology in, but I've just given up on that because it just does not work in this format.

I'm sorting out where we're going to look at next, but most likely it'll be our first introduction to Dionysus, and the start of multicellularity...

[minimumsky5]

Vitrellus, 50 million years after formation. A small river, laden with metal ions leached off the surrounding mountains, reaches the ocean through a lagoon formed by the action of waves, as they move sediment along the coastline. In the sky, a break in the lower cloud deck allows us to see the high altitude SO2 clouds that moderate this planets climate.

Most terrestrial planets in the Yggdrasil system are similar to Earth, in the sense that they have oceans of liquid water, an active water cycle, and oxygen/nitrogen/argon atmospheres. Vitrellus, however, is a significant exception. Vitrellus accumulated significantly more sulphur than the other terrestrial planets, and as a result it's oceans are composed of 67% sulphuric acid, and it's clouds are arranged into three bands of sulphuric acid, water, and sulphur dioxide.

This has very serious implications for the planets climate, as the normal silicate weathering cycle that occurs on Earth cannot function. Carbonates that are eroded from the land are destroyed upon entering the global oceans, and so cannot be sequestered, but carbon dioxide is constantly erupted from volcanoes just like on Earth. This would have eventually caused the planet to enter a runaway greenhouse state and loose all its water, if not for a very fortunate chance event very early in the planets history.

The oceans of Vitrellus are supersaturated in silica due to the high erosion rates caused by the acidic rains, to the point that it readily crystalizes around any solid particle suspended in the water. As a result, early prebiotic chemistry on the planet focussed around lagoons and estuaries, where the silica crystals were less of an issue. The earliest lifeforms were able to make use of abundant carbon during a very early phase of Vitrellus's history when the atmosphere was highly reducing, in a similar way to Earths, but as the acidity of the oceans increased, the organic molecules were destroyed faster and faster, until only pure carbon was left to rain down in huge layers of graphite on the bottom of the oceans.

Early life was forced to adapt to this new, low carbon environment, and to do so it started to incorporate silicon into it's chemistry. This began when some cells began to store silicone polymers in large storage organelles, as a form of carbon storage that is stable in highly acidic environments. This is not very efficient in either mass or volume, but other forms of carbon storage require active energy usage and advanced membrane filters to keep acids away from the cell. These cells were quickly able to start using silicone more broadly in their metabolism, in particular as a form of data storage analogous to DNA (which they had been using up to this point). This new clade of cell, the Vitromopha, would quickly spread around the planet, and at this point in it's history, have successfully outcompeted the original DNA clades, with the last of them dying out a few million years ago as rising acidity destabilised their delicate DNA sequences.

The landscape of Vitrellus would seem quite bland and muted to a human traveller, even accounting for the lack of green plants. Any metals in the crust are quickly oxidised to red and brown oxides, which dissolve into the acidic rivers and streams, and are concentrated into the global ocean. The ocean itself is at the saturation point of silica, and so generally appears a milky brown colour, but occasionally blooms of Vitromorpha cells clarify the water as they consume the silica to make silicones. When these blooms die, they sequester carbon as silicones back into the crust.

[minimumsky5]

I realised that I never actually put the stats for the objects in the Yggdrasil system in my last post, so here they are for those wondering:

Yggdrasil itself: Stellar class, M1V BY Dra Mass: 45% of Sol Luminosity: 3.3% of Sol Radius: 41.5% of Sol Effective temperature: 3811K

Hephaestus: Mass: 3% of Earth Radius: 30% of Earth Orbital Radius: 0.071 AU Year Length: 10.7 Earth days

Laki: Mass: 8% of Earth Radius: 44% of Earth Orbital Radius: 0.1 AU Year Length: 17.22 Earth days

Methuselah: Mass: 18% of Earth Radius: 58% of Earth Orbital Radius: 0.125 AU Year Length: 24.06 Earth days

Vitrellus: Mass: 45% of Earth Radius: 78% of Earth Orbital Radius: 0.151 AU Year Length: 31.95 Earth days

Thalia: Mass: 120% of Earth Radius: 122% of Earth Orbital Radius: 0.175 AU Year Length: 39.86 Earth days

Dionysus Mass: 80% of Earth Radius: 96% of Earth Orbital Radius: 0.2285 AU Year Length: 59.47 Earth days

Avalon/Eden Mass: 250%/210% of Earth Radius: 129%/122% of Earth Orbital Radius: 0.3 AU Year Length: 89.46 Earth days Mutual orbital radius: 145,000km Mutual orbital period: 71.169 hours

Anguta: Mass: 12x Earth Radius: 214% of Earth Orbital Radius: 0.45 AU Year Length: 164 Earth days Parvati: Mass: 450x of Earth/1.5x of Jupiter Radius: 13.56x of Earth Orbital Radius: 1.2 AU Year Length: 1.95 Earth years

Odin: Mass: 150x of Earth/50% of Jupiter Radius: 13.55x of Earth Orbital Radius: 4 AU Year Length: 11.92 Earth years

Amun: Mass: 35x of Earth Radius: 6.56x of Earth Orbital Radius: 8 AU Year Length: 33.74 Earth years

Persephone: Mass: 8x of Earth Radius: 275% of Earth Orbital Radius: 12 AU Year Length: 62 Earth years

[minimumsky5]

So, it turns out, drawing planets is hard....

Anyway, here is the system we will be following as life develops on multiple planets, with the sizes to scale, but the distances obviously not! The system is shown as it would appear 5 billion years into its history. Tidally locked planets are shown with their sub-stellar point pointing at the observer.

Lets start with the star, the energy source for the entire show. Yggdrasil (Norse tree of life, and foundation of the universe) is an M1V BY Dra star, which when translated to English means that the star is a large red dwarf (nearly at the limit of M class), but it is also a BY Draconis variable, meaning that its starspots are so big, that they can significantly reduce it's light output. This star is expected to have a main sequence lifespan of 225 billion years, but as with all red dwarfs, its luminosity will increase significantly more proportionally than Sol's will, so its habitable zone will end covering most of its terrestrial planets for at least some part of it's lifespan.

Hephaestus (Roman god of fire and the forge) and Laki (named after a particularly destructive Icelandic volcano) are the two innermost planets of Yggdrasil. They are both hot, small worlds with large iron cores, similar (though smaller and a little cooler) to Mercury. By 5 billion years into the systems history, Hephaestus's mantle has cooled and solidified, but Laki alternates between a resonance state with Vitrellus and one with Thalia, meaning that it maintains a constant volcanic output driven by tidal forces, even though a planet of it's size should have no primordial heat left. Laki was on the cusp of habitability, but it's high volcanism resulted in a runaway greenhouse event that stripped it of its water early in it's history, leaving it with a roughly 2 bar atmosphere of CO2 and SO2.

Methuselah (named for the biblical patriarch, said to have lived for 969 years) is our next stop, and unlike Laki this world is the first one to be able to hold onto significant water. However, due to it's proximity to Yggdrasil, its water cycle is very different to Earth. At it's equator, it is too hot for rain to reach the ground, and so it's tropics and mid latitudes are parched deserts with only very rare oasis providing any moisture. At the poles, however, water can condense, and these small seas provide Methuselah with 2 very habitable areas for life. Methuselah is a small planet, twice Mars's mass but much smaller than Earth, but it is locked into a complicated resonance with Thalia and Avalon/Eden, one which will remain indefinitely, and means that Methuselah is capable of sustaining plate tectonics despite it's small size.

Vitrellus (named in reference to Oil of Vitriol, an old name for sulphuric acid) is the most alien of all the worlds in the Yggdrasil system. This world, half the mass of the Earth and nearly the same radius, has a much higher concentration of sulphur and sulphur compounds in its crust, meaning that it's oceans condensed not as water, but as a strong solution of sulphuric acid. Despite this incredibly hostile chemistry and hellish temperatures (regularly reaching 90 degrees Celsius at the equator), Vitrellus has an active and diverse biosphere based on silicon, carbon, and sulphur compounds.

Thalia (named for the Greek Charity of fertility and plants) is a planet somewhat larger then Earth, which due to it's size accreted a large envelope of volatiles onto its surface, forming an ocean nearly 50km deep on average. This layer of volatiles also created a thick atmosphere and a strong greenhouse effect, creating surface temperatures just barely below the critical point of water, where the boundary between the ocean and atmosphere becomes indistinct. No life survives down there, but the cloudtops maintain habitable temperatures despite the torrid conditions below, allowing huge blooms of skyplankton and other attendant organisms to flourish, turning the planet a strong green colour.

Dionysus (named for the Greek god of festivity and insanity) is the closest thing to the traditional picture of a tidally locked world orbiting a red dwarf that Yggdrasil has to offer. It has the traditional swirl of cloud surrounding it's sub stellar point, and at this point in it's history an ice sheet surrounding it's terminator. The planet currently has an active surface biosphere, but this is only a temporary feature. Dionysus goes through regular cycles of huge build ups of carbon dioxide in it's atmosphere, up to 1-2 bar, followed by equally massive drops in CO2 levels down to just a few parts per million, caused by continents passing through it's central collection of storms. Life on Dionysus is one of times of huge plenty, and vast catastrophes.

Avalon/Eden are the jewels of the Yggdrasil system, a pair of habitable superearths locked in orbit of each other. Both of these worlds are ideal candidates for life; large mineral rich oceans, plate tectonics to allow for carbon cycling, and their mutual tidal forces will keep their interiors warm and convecting for billions of years. There is one current difference between themselves and Earth, however; as these planets are currently towards the outer edge of the habitable zone, they have large CO2 dominated atmospheres, nearly 2 bar each, just to keep warm. These planets will be the centre of attention for this project, and along with Methuselah, will maintain life for the longest time.

After the Avalon/Eden system is a rocky asteroid belt, containing twice the mass of Sol's asteroid belt, followed by an interloper from the outer reached of the system. Anguta (named for the Inuit creator god, and god of the underworld) is a waterworld that initially formed outside of the gas giants in the system, before an encounter with Persephone saw it swing into the inner system. A combination of another encounter with Parvati, and drag from the original system asteroid belt (now carved in 2 by Anguta), caused it to settle into a circular orbit. Anguta is currently right at the outer edge of the habitable zone, with it's surface locked in ice and only a thin, nitrogen dominated atmosphere, but as Yggdrasil grows in luminosity, this is unlikely to last.

Our next stop is the queen of the system, the largest planet of Yggdrasil, Parvati (Hindi goddess of power and beauty). Parvati is a large gas giant, 50% more massive than Jupiter, with a large collection of rocky and icy moons, and rings to rival Saturn's.

Odin (Norse god of wisdom and healing) is the second gas giant of the system. It is about half the mass of Jupiter, but due to the effect of gravitational compression, Parvati and Odin are almost the same size, to within a few dozen kilometers. Odin has a thin set of rings, but has 4 major moons locked into a Laplacian resonance.

Amun (Egyptian god of the sky and wind) is the systems only ice giant, an azure gem shining brightly due to methane in it's atmosphere granting it a brilliant blue colour. Occasional clouds of methane occur in it's mid latitudes, and around storms in it's tropics.

Persephone is the final planet, an Eris like object in it's outer system, covered in a homogeneous layer of ice that was deposited from past volcanic paroxysms.

[minimumsky5]

Earth, eventually, will die. Regardless of how us humans treat it, the planet is cooling down internally as it runs out of radionucleotides to warm itself, and at some point, hundreds of millions of years in the future, it's mantle will freeze, and all tectonics will stop. Without a stable source of greenhouse gases, the planet will cool, until it is permanently locked in ice. Not only that, but our sun is, very slowly, warming as it ages. If the Earth does not freeze in time, its oceans will boil away, to be lost to space forever.

These are the two possible fates of all terrestrial planets, and all will meet them at some point. However, they will not all meet them at the same time. More radionucleotides in the core, a smaller, longer lived star, and tidal heating from close planetary companions, could keep a planet going for far longer than Earth. Earth has had 4.5 billion years for it's biosphere to evolve, diversify, and diverge into it's dizzying array of lifeforms. Image a planet where life has had 10, 20, 50 billion years of habitable time to innovate new ways to live, new bodyplans to compete with each other, even whole new types of chemical substrates on which to live.

That is what this, currently untitled, project will explore. A set of habitable binary planets, orbiting an M1 class red dwarf, kept warm by their mutual tides that they raise on each other, illuminated by a star that will last for over 200 billion years. There will be other planets to explore, and some of them may also be clement enough for their own biospheres, but they will not last as long as our two main contenders.

For now, though, we need to introduce our planetary system, and set the scene, in the next few posts, on what life will be working with as it explores every pathway it can.