by Alex van Daalen, G12
People have long asked the question of whether or not we are the only forms of life in the Universe. Our scientific and technological advancements continue to offer clues about what is out there in deep space, and provide indications of the humbling prospect of the existence of other walks of life. On Earth, life exists in an array of shapes and sizes within the millions of species of fauna and flora. But as we look outwards, away from our home planet, what other forms of life can we expect to find in the cosmos?
Of all the possibilities there may be, life will be restricted to the same chemical and physical laws that we know of. Nevertheless, it can adapt and morph into forms that would be inconceivable to us in environments of their own, undergoing their own complex evolutionary processes.
“Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.“
Arthur C. Clarke
Life as we know it
Alien life could be more Earth-like than we think. Carbon is one of the most common elements in the universe, and is very good at forming large, stable molecules. Its versatility makes it one of the fundamental building blocks for life. If carbon based life forms are found elsewhere in the universe, we would be cosmically related.
The argument of convergent evolution suggests that on planets with similar conditions to ours, we could potentially see very similar life forms. The various features of living organisms on Earth such as eyesight, flight and echo-location which we see today across the wide range of species in unique and independent ways have all been adapted over millions of years. If the evolutionary process occurs on other planets, there is the possibility that we could discover certain universalities of life where we would find the most successful biological features. Each would be tuned to adapt to its surroundings, like nocturnal animals or those adapted to harsh temperatures and environmental pressures. Could we then expect human-like organisms to exist on other planets that have followed its own complex chain of evolutionary events? This is highly unlikely due to the complexity of the timeline of human evolution, and the conditions on Earth. But animals are not the only forms that adhere to convergent evolution; plant life has adapted in many different ways of its own.
Would alien plant species look like ours, or something entirely different? The green appearance of plants on Earth is a result of the absorption of other wavelengths in the Sun’s light spectrum. But alien plants would evolve and adapt to their own Sun’s spectrum, giving them unique colours. Around hotter stars, plants could appear more red by absorbing the higher energy blue wavelengths or black around dimmer stars by absorbing all the visible light available. NASA scientists recently discovered a purple-pigmented molecule named retinal which predates the green-pigmented chlorophyll responsible for photosynthesis. Early life on other planets could then appear purple instead of green, creating a biosignature that can be seen from lightyears away.
The conditions of life’s home planet would be the most important factor in determining what may be there. Super-Earths with strong gravity limit the growth of life on the surface, but in seas and oceans the effect of gravity is mitigated. It’s when life that originates in the water comes out on land and feels the force of gravity that then necessitates the growth of bones, muscle mass and more robust circulatory systems. Smaller worlds with weaker gravity could facilitate life underground, protecting it from extreme temperatures and deadly cosmic rays. But surface life on planets of fractions of the Earth’s mass could produce plant life that grows to towering heights or animal types without bones and muscle mass. Complex life of this size may still be unlikely, so we can look even deeper down to the microscopic level.
Microbial life may be the most robust, versatile and adaptable of all forms of life and would be a profound discovery. In the millions, microbes could build up into huge entities that envelop the environment around them, leaving behind a distinct biosignature and exhaling gases that wouldn’t otherwise coexist naturally. Detecting abundant and consistent levels of oxygen, carbon dioxide and methane could be a potential sign of life harbouring planets.
Life may not only have planetary origins — though most Stars are too hot to maintain life, the atmospheres of brown dwarfs may provide ideal temperatures, pressures and chemicals for habitability. Seas of dense gas could hold adapted versions of photosynthetic plankton, and strong gaseous upwinds may even support larger complex life.
“If just 1 in every 100 trillion Earth-like planets produced a human-like form, there could still be thousands of creatures like us out there.”
Life as we don’t know it
Exotic biochemistries based on silicon could avert the limited temperature parameters that suit liquid water and carbon based life. Places outside our habitable zone that seem wildly hostile to us require matching exotic biochemistries. Silicon is less prone to forming large molecules like how carbon does, but is able to withstand a wider range of temperatures. Another problem is that when exposed to oxygen, it binds and forms silicates; rock-like minerals. Silicon based life would need to exist in the absence of oxygen, and may use other biochemical processes to derive its energy such as chemosynthesis by breaking down rocks. A bizarre suggestion is that in higher temperatures silicon-oxygen bonds may be more flexible, proposing the existence of life forms inside molten silicate rock. This may allow life to live in molten magma chambers, meaning alien life may even exist deep below the Earth’s surface.
Clouds of cosmic dust that make contact with plasma produce a strange phenomenon found only in simulated conditions. Spontaneous self-organising dust particles which form helical structures that resemble DNA may be an unexpected form of life. But these so-called plasma crystals even exhibit life-like behaviour by replicating more stable forms and passing on information. It’s debatable whether or not this can be called life. However, if these evolving plasma crystals really exist, they could be life’s most common form. The hearts of ultra dense neutron stars, where particles are crammed together producing a hot dense sea of subatomic particles, may harbour life based on the strong force. The binding of nuclei to form macronuclei and even larger heavier particles may be a form of life that exists in a sea of particles with incomprehensibly fast life spans. Though life in this form may never be discovered.
An unconventional idea is that life doesn’t have to evolve naturally, but can instead be produced and designed. Synthetic and machine based life, free of the typical biological limitations, could thrive in places no other forms could. In extreme temperatures and in the vacuum of space, the possibilities are almost endless. Artificial life that is exposed to the evolutionary process may develop exponentially faster than biological life, and these self-replicating technological beings are estimated to be able to colonise an entire galaxy in as little as a million years. Machine intelligence, based on the electrical properties of silicon, may be the apex of the evolutionary process and the universal endpoint for life. This suggests that biological life may only be a starting point for a sprawling chain of intergalactic life in the distant future of the universe, one that we as humans may even be contributors to.
As of today, life as it exists on Earth is the only form that we know of, but the endearing prospect of finding other walks of life in the universe may widen our scope and give us an insight into who we really are as a human species.
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Cover Image Courtesy of “LIFE BEYOND II: The Museum of Alien Life”, 2020
