#i think in all likelihood it was actually another antelope species

[neofelis----nebulosa]

People are way too comfortable with admitting stuff. I was at the zoo and someone remarked that she didn't remember what addaxes were called, but that she knew her brother has one's head on his wall. They're a critically endangered species 😬

[bluethepaladin]

so im like super excited to meet the aliens in ur next chap of when i dream it happens in blue. ur like so smart in science and stuff. what about the science of aliens? is that a thing? how do u make urs? do u know anything about it?

Thank you, dear anon, for this ask about life. Also thank you for reading when I dream it happens in blue. I’ve gotten overwhelming support on this fic and I am just blown away by how much you all love it.  I was honestly waiting for an ask like this because I love aliens and creating alien societies. Also, thank you for being patient with me as I get around to answering these asks.

Basics of Life

So first of all, when considering life in any discussion, I am going to make the fundamental assumption that advanced life-forms must either evolve from more primitive life forms, or they must be created by other advanced organisms that already did so. Therefore you can’t have humans or alien counterparts on some other planet without a whole web of interdependent plants and animals that surround them, and a whole chain of ancestors that led from a raw plant to an ecosystem. There might be a hypothetical exception to this rule, maybe on a planet where one life-form has wiped out all other natural life forms, but how that happens is up to your creative exploits.

When we think about life and how it develops, we have to draw from the only example we know of where it happened, aka. Earth. And as we have no eyewitness accounts for how this happened we are again forced to heavily rely on inferences and experiments that have been widely regarded as accurate within the scientific community.

But what’s even worse for us writers is that we have no actual scientific evidence of how typical what happened on Earth actually is! But since it’s all we have we just gotta work with it. But keep this in mind! (It’s actually pretty cool to think about, too) At first glance, it seems like our little planet offers an enormous range of life-forms all so obviously different that one might suspect them of representing a large sample of independent instances. Earthly life-forms include protius bacteria, komodo dragons, octopus, cacti, antelope, hummingbirds, coral reefs, orcas, redwood trees, and us–just to name a very, very few. Seems pretty diverse, right? Especially when you consider there are lichens that grow in the frigid wastelands of Antarctica, and fish living in hot springs that would cook a regular fish. If we take into account all flora and fauna that have ever existed, well that includes things like the stegosaurus, ammonoidea, mammoths, and giant dragonflies, the sample gets even bigger. Surely, surely this is a diverse lot, but if we look at them at a fundamental level, they are all so similar they are in all likelihood products of a single biogenesis. What scientists mean when they say this, is that all terrestrial life is, in a real and important sense, just one example with many variations on a basic theme. 

While that may seem like an extreme statement, there’s a great deal of scientific evidence to support it, a lot of which has just been discovered in the last few decades. It’s not easy to define life, especially with only our terrestrial examples to work with. But as far as we can tell, all life, no matter what form it takes, has these things in common:

they are highly organized structures

take in energy from their surroundings and use it to maintain their structure and organization

have the ability to reproduce, i.e. to make exact working copies of themselves (more or less).

Each of these statements is subject to some qualifications and clarification, of course (not every individual actually uses the ability to reproduce, and the offspring of sexually reproducing species are almost never identical to their parents) but even taking this into consideration, these are all characteristics that we expect of any life form on Earth.

Terrestrial organisms acquire energy they need to maintain themselves in a variety of different ways. Until recently, we assumed that all living beings got their energy from the sun, whether directly or indirectly. Green plants use sunlight directly, combining it with water, minerals, and carbon dioxide as raw materials which in turn makes carbohydrates and fives off oxygen. They then store that energy in their own tissues. Fungi or animals get their energy from eating those tissues and metabolizing the carbohydrates and giving off carbon dioxide that can then be reused by plants. But then we have another level, the carnivores, who eat the animals that eat the plants. There’s also smaller organisms who eventually recycle the bodies of other dead organisms into the soil as nutrients for the plants. This is the most elementary summary of the science of ecology, and I highly recommend reading more about it to make your aliens more accurate! From this we know that no organism exists in isolation, but all organisms interact to maintain cycles of chemical reactions repeating, with chemicals being reused repeatedly and energy being the only substance added from outside sources.

The essential input, as we now know, is energy, not necessarily solar energy. As we discovered, we can no longer say, even on Earth, that the sun is at the center of all energy cycles. Recent deep ocean explorations have discovered whole ecosystems based on chemical synthesis on the ocean floor, much too deep for the sun’s reach. The food chain in this ecosystem starts with microorganisms that metabolize directly hydrogen sulfide and minerals in the warm water that seeps up through vents from Earth’s interior.

The CHON System

All terrestrial life, from the tiniest bacteria to human beings is based on the same fundamental biochemical architecture. It uses the same DNA to make the same protein building blocks: the diversity comes in on how they’re arranged. The building blocks of life on earth is largely based in four fundamental elements: carbon ©, hydrogen (H), oxygen (O), and nitrogen (N), where the acronym CHON comes from. A few other elements are also vital in specific applications. Phosphorus is fundamental to the basic energy transfer reactions used in living cells. Sulfur is also crucial to some aspects of terrestrial life.

Carbon is the backbone of the CHON system. It is the only element that makes arbitrarily complex linkages to itself and because of this it can build up extremely complex molecules. Another major component to life on Earth is liquid water. Life in general would probably require some solvent that all its magnitude of chemical reactions can take place in. Water works well because it’s made of common elements–hydrogen and oxygen. Hydrogen actually makes up most of the universe. Of the heavier elements, oxygen is more common but in the grand scale of the universe is much more rare than hydrogen, due to the fact that it’s most common isotope is exceptionally stable. Overall, this means that water is actually one of the most abundant substances in the entire universe!

But water has some unusual properties too. It has a high boiling point and it’s temperature range means that it has a very large range in which it stays liquid. This is convenient when world building because planets vary in temperature form place to place. Water is also a near-universal solvent. It can dissolve virtually anything to at least some degree. A solvent is necessary for biochemical reactions, and this makes water a great contender by making it easy to move things around–like food and oxygen and waste products–but it also provides a medium in which the basic building blocks of life can move around.

Probably one of the more interesting things about water is that it expands when it freezes. This is extremely unusual: most liquids are less dense than the solids they melt from. (There are also different forms of ice. Ice I occurs on Earth, the normal stuff you find in your freezer and in glaciers and is the only kind less dense than water. But Ice II and Ice III can form under immense pressure and most likely exist in icy worlds in other parts of the universe). This property of Ice I is very important for Earth’s climate regulation. 

Other Possibilities

We are now venturing into the world of hypotheticals. All of the examples of planets I give are mostly derived from science fiction I’ve read or watched, and are all plausible, even if we can’t identify any specific examples in our small solar system.

Hydrogen Fluoride WorldIf we base a planet on the halogens, or the elements that range from fluorine to astatine (group 17), then there are some comparisons to be made between a potential oxygen/water world. Free fluorine could act as a sort of oxygen element and hydrogen fluoride (HF) would make a substitute for water. By this I meant that it would form lakes and oceans and be the solvent in which the biochemical reactions took place. In a system such as this, plant life would release free fluorine during photosynthesis, while animals would breathe in fluoride instead of oxygen. 

There would be some technicalities in using such a world–factors come into play such as the fact that fluoride is comparatively a much rarer element, and the fact that fluoride is a much more reactive element which would make it hard to accumulate in the atmosphere, but it’s up to you how you’d like to solve these problems, if you acknowledge them at all. 

Ammonia WorldSince water is such a good solvent for biochemical reactions, it’s been an object of science fiction writers’ obsession to try and find an alternative. One possible is liquid ammonia. Ammonia is also made from common elements–nitrogen and hydrogen–so it’s common in the universe. Ammonia is a great solvent and it also has a large temperature range where it remains liquid and has a high boiling point. One major difference is that ammonia ice sinks, so ice would sink to the bottom of the ocean. Although, that could still technically work as a climate regulator: the ice at the bottom of the ocean would be extremely hard to melt and help cool the atmosphere. 

Because of scientific factors like the greenhouse effect causing a thin atmosphere, and the fact that such a world would have to be frozen to be sustainable that it would be near impossible to extract ore from the rocks to make metal, would likely mean this type of planet would never get past a Stone Age without outside influences. 

Sulfur Dioxide SeaAn additional candidate as an alternative to water and has the fun bonus of containing sulfur is the idea of the sulfur dioxide sea. In our solar system, there’s actually a planet in our system that has a sulfur dioxide sea. Jupiter’s moon Io, however is covered in ice and is therefore unlikely to contain life (but there’s speculation about beneath the surface, but I digress).

Like water and ammonia, sulfur dioxide has a long liquid range and a relatively high boiling point, although it is important to note that the atmospheric pressure would have to be at least 3x that of Earth’s in order to maintain it in liquid form without boiling at a reasonable temperature. Sulfur dioxide ice also sinks. 

An interesting factor of such a planet is that there would be no oxygen in the atmosphere, otherwise sulfur trioxide would form, which is solid at room temperature. This means that the sulfur dioxide sea would likely lap against shores of pure sulfur and the atmosphere would be largely made up of nitrogen and interestingly enough–sulfur dioxide! Yeah, the compound that makes up the oceans would also make up a large part of the atmosphere! Higher life forms would have an interesting development because fire would be impossible on such a world.

Notes:

Thanks for the ask! I love thinking about aliens and creating them from the ground up. When you do it that way, you start to think how the environment and the physical aspects of the occupying planet actually can affect the aliens and their culture. I hoped this helped you! Don’t forget, you are free to tag me in or send links to me of your stories and fics so I can check out the cool sci fi aspects! Also, my askbox is always open. You can find more science answers under the tag #blue answers.

love, Blue