Every single life form we have ever encountered requires water. And all of these organisms that seem to be very different are built from the same code. Much like how every computer program is made from bits of 1’s and 0’s; life as we know it is built from DNA. Adenine, guanine, cytosine, and thymine (or AGCT) are the chemical letters of this code. And with just these four chemicals, DNA has coded for everything that swims, runs, lives and dies. But without a proper medium, the almost magical chemistry of DNA cannot unfold; this is why all life requires water. Well, at least this is the case on Planet Earth.
To make the claim that all life requires water and DNA would be to base our assumptions on the only life we know of: life on Earth. The problem with this line of thinking is that we would be operating with a sample size of one. In the scientific community, this would not be enough data to make a educated hypothesis. What might be the ideal biochemistry for life on Earth, would not be the same for a planet with different temperatures, gravitational fields, chemistry, seasons, and so on. In fact, life on another planet may be so strange that we might mistake it for not being alive at all.
In order to determine whether life could arise without water, we must first decide exactly what we mean by life. By Darwinian standards, all life must be able to reproduce, grow, be active, and change continuously before death. This is a great reminder of what it means to be alive but still, what “is” a living thing? It is so recognizable once we see it but then again perhaps we are only capable of recognizing one kind of life. What is it that makes us sad when we see a dog get run over by a car, but not when we see a computer get smashed by a hammer?
Life seems to be self organizing. While the entire universe is often moving towards increased disorder or entropy, the closed system of a living organism is fighting to maintain order. As we age, our bodies lose the ability to organize themselves as they decay and die. All diseases we know of are agents of exacting disorder, cancer is the prototypical example of this type of entropy proliferation within the body as it causes cells to mutate and multiply uninhibited.
So what does it take to become a self organizing, closed system capable of growth, reproduction, and continual change? Well to be fair, we already have computer programs and mechanical robots that do all of these things without any water at all. So often we think of ourselves as unique chemistry and conscious beings, but there is no scientific evidence for that proposition. We are made from the same stardust that makes all things in the universe, and there is no definitive way to prove that you are in fact conscious or instead a robot that is saying all the right things. The truth is that we are self replicating robots, and we are looking for others that we might believe are alive. In that case, I do not see why water is required.
However, robots are a product of human imagination and creation. The scientific community is much more interested in spontaneously forming life, that is to say, life that does not involve human interaction. This search has us scanning the universe for any planet or moon that contains liquid water. Although, if we expand our search to simply require a medium for mixing of complex chemistry: then we can set our eyes on on a broader range; including one of the moons of Saturn, Titan.
On Christmas Eve of 2004, the Huygens space probe detached from the Cassini spacecraft orbiting Saturn and began a 20 day decent onto the surface of Titan. This was a very merry Christmas for the teams at NASA JPL, but the real present would be in the form of piles of data that we are just now starting to unwrap today.
Titan has large liquid lakes of methane that resemble the Great Lakes of North America, and this may be just the medium necessary for life. It is very cold on Titan. Water is only found in its frozen form but chemicals that would be gaseous on Earth take on liquid form.
There is not as much energy available in these methane lakes as Earth, so it would make sense that the formation of life would be prolonged. These organisms would move at a much slower pace and chemical interactions would take much longer to organize into life. But generating chemical energy in a methane medium is entirely possible, and not even entirely foriegn.
Scientists have been studying the data of the Cassini-Huygens mission to Titan since its 2004 Christmas decent and found a surprisingly low amount of CO2 compared to methane. This has been speculated to be due to organisms converting CO2 into methane for chemical energy, much like extremophile methanogen life does on Earth. These organisms do live in environments with water on Earth, but with extremely low oxygen conditions, they have evolved to create the key to chemical energy in DNA based life, ATP, by utalizing CO2. Perhaps life on titan is evolved to survive in these large methane lakes on Titan, or even stranger, perhaps the life on Titan created these methane lakes and now is struggling to adapt to the world it drastically changed. This era of life on Titan could resemble early life on Earth that diminished CO2 levels in our atmosphere and replaced it with oxygen which then allowed for the development of aerobic life.
In addition, other studies have shown that there are chemical reactions occurring on Titan that are generating complex organic chemistry. Most notably is the formation of polycyclic aromatic hydrocarbons, which are critical to life on Earth. The formation of these chemicals demonstrates a level of complexity that could be suitable for or indicative of the presence of life.
If this is the case, then micro-biotic life could be swimming around in the great methane lakes of Titan. However, the chances of this are small enough for there to not be considerable interest in funding a mission to scan for life on Saturn’s moon.
Could this assessment of the chances of life on Titan be biases by our opinion that life can only exist with liquid water? Absolutely.
However, if life is not a product of any sort of divine intervention, it would seem an eventuality that any complex molecular soup like this should eventually stumble upon self generating closed systems.
Water is quite unique and I could rattle off a list of its characteristics that allow for life, but that only applies to life as we know it. Any life that does exist out there in the universe is likely to not be anything like life here on Earth. And if we only look at the universe through Earth shaded glasses, how can we ever find something novel amongst the stars?
Most scientists would argue that life was bound to happen on Earth. With the right conditions, life is commonly thought to simply arise like a law of nature manifesting itself. But if life truly is a law of nature, then it would seem to be one of self replicating systems spontaneously forming from randomized complex interactions. And with enough time and complexity, life should be able to form in any medium. Limiting our search to water seems so small minded. If life is an eventuality, we should eventually find it everywhere.
Conway’s Game of Life:
Video of Titan lakes via NASA: