Life on Earth and beyond – Part 1
The question of whether or not life, either simple or complex, exists elsewhere in the Universe is not an easy one. It’s a popular opinion that because life exists on Earth then it must have easily sprung up in other places as well. This is an expression of the ‘Principle of Mediocrity’ or the ‘Copernican Principle’ which is the idea that the Earth is just an ordinary planet that is not in any way special. An opposing view is that the life is so complex and so unlikely that we could well be the only place where it has occurred.
For life to have arisen in all its complexity by blind physics and chemistry working on the components of the newly formed Earth billions of years ago doesn’t sound very likely to me. Unfortunately, no one has worked out the exact details of how it occurred and if someone could do that then we might have an idea of how likely it was for life to come into being.
As it is we have only been able to observe a sample of one and any conclusions that we might try to draw from what happened on Earth is on somewhat unsafe ground. It’s perfectly possible that Earth is the only planet with life on it in the entire observable universe and that nowhere else has any life at all, even simple single celed organisms.
But if Earth was the only place in the Universe with life on it, how would we know? Suppose the nearest planet with complex life was in a galaxy 100 million light years away, which is not all that far away compared with galaxies over one hundred times as distant that have been imaged by the James Webb Space Telescope. If that planet had a civilization with a technology similar to ours then it’s hard to imagine how we would detect it. Any radio broadcast they made would have to be immensely powerful for us to be able to receive it.
If by some means or other we could detect radio waves from a technological civilization at a distance of 100 million light years and could then travel there instantly we would arrive 100 million years after the transmission was made by which time the source of the signal would have probably disappeared without trace. A Universe in which technological civilizations were separated by, on average by 100 million light years, would contain a million or so such societies all of which, most likely, would be unreachable and unknowable.
NGC 4414 imaged by the Hubble Space Telescope in 1995. It is about 62 million light years away.
Well, maybe technological civilizations are very rare, but surely simple life must have arisen anywhere that the conditions were suitable? Possibly, but it’s not a given. Deoxyribonucleic Acid or DNA plays a central role in the transmission of characteristics from one generation to the next.
A model of the DNA molecule. Each rung has four possible configurations forming an ‘alphabet’ which can describe all the different proteins in every type of life.
DNA is a double helix in which information is encoded using only four groups of atoms called bases. Proteins in our bodies and in all other types of life, contains long chains of so-called amino acids, hundreds of units long. Each amino acid, of which there are 20 types normally occurring in living organisms, is encoded by a sequence of three bases on the DNA molecule and the order in which the amino acids occur on the protein chain is crucial to its function although it might be possible for more than one sequence to have the same effect.
How DNA and the system for encoding the order in which amino acids occur in proteins arose by itself is a mystery. On the face of it, it seems almost impossible that such an elaborate arrangement could have arisen by chance. It has been suggested that DNA could have somehow arisen in stages from single strand RNA although the details are by no means clear.
According to https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7459455/ there are 20,365 different proteins in the human body including 3428 enzymes which are proteins than enable biochemical reactions in our bodies. For all these proteins and other substances to have come together to form a wide variety of interacting structures and maintain an elaborate symphony of thousands of chemical reactions must have taken a remarkable sequence of events. It is also remarkable that the instructions to make all these proteins are contained in microscopic sperm and egg cells using an elaborate code that seems to have invented itself.
It’s no wonder then that there are a range of ideas that attempt to overcome the apparently low chance of life arising by itself. One idea is that there are a vast number of parallel universes in which everything even remotely possible has happened. So that even if it was vanishingly unlikely for life to arise by random chemical and physical processes then we are living in one of the rare universes in which it has happened.
The Multiverse by JuliusH on pixabay
Parallel universes are also used to explain the what is called the ‘Goldilocks Effect.’ The fundamental forces of nature appear to be ‘just right,’ for us to exist, like the things that Goldilocks encountered in the house the three bears. One manifestation of the Goldilocks Effect is the balance between the strong nuclear interaction that holds the nucleus of an atom together and the electromagnetic force that tends to force it apart.
If the strong interaction was only a little bit weaker then it would not be possible for hydrogen to form other elements in stars by nuclear fusion and hydrogen would be the only element in the universe. If the strong interaction was only slightly stronger then all the hydrogen atoms in the universe would tend to pair up to form nuclei with two protons which would be a form of helium and there would be little or no hydrogen in the universe. In both cases we would not exist.
The Jewish book of Genesis, which is also included in the Christian Bible states that God created the world and all the life in it in six days.
Michelangelo – Creation of Adam – Sistine Chapel
The Koran which has many parallels with Jewish scripture also has God creating the world and everything in it in six days. Other religions have their own creation stories. Some religious fundamentalists hold rigidly to the timetable set out in the book of Genesis and have worked out that the world is only around 6,000 or 7,000 years old. Most famously James Ussher Archbishop of Armagh and Primate of all Ireland stated in 1654 that the Creation took place in 4004 BC.
We shouldn’t blame Ussher for coming up with what, to many people today, sounds like a ridiculous answer but he was working from the only sources he had available. In the centuries since Ussher it has become widely accepted, even among many religious people, that the Earth is around 4.5 billion years old and that life appeared nearly 4 billion years ago. However, some people stick rigidly to the idea that God created all forms of life at the same time only thousands of years ago and that evolution is somehow an illusion
The case for evolution is very strong. There is a large body of evidence to support the view that life on this planet developed by many stages from relatively simple single cell life to the wide variety of complex life we see around us today. But how did it happen?
Statue of Darwin in the Natural History Museum, London.
Charles Darwin proposed that small changes in offspring would give some organisms a better chance of surviving than their parents and that over time new species would emerge. This is known as the theory of the origin of species by natural selection. This idea has been expanded by biologists following the discovery of how DNA passes on information and today if someone says ‘evolution’ they mean the modern version of Darwin’s theory of how evolution happened. Any other explanation is generally not considered.
We can see natural selection at work in bacteria that develop resistance to antibiotics and pesticide resistant insects. But natural selection might not be the whole answer. The genetics of fruit flies have studied for over a hundred years including subjecting them to chemicals or radiation which increase the likelihood of mutations. In all this time many strange insects have been produced, but they’re still fruit flies and there is no sign that a new type insect is going to emerge from these experiments. Fruit flies can produce a new generation every 10 days or so and therefore have the potential to evolve hundreds of times faster than people but they seem well settled in their ecological niche and are not going anywhere.
The theory of ‘intelligent design’ proposes that at least some aspects of evolution cannot be explained by ‘natural’ events and that something must be guiding it. This is not always expressed in religious terms but one way of looking at intelligent design is to say that God is influencing the development of life. The idea that we are living in a simulation also puts an external intelligence in charge of evolution. It’s very convenient to be able to explain away anything we can’t understand by invoking a supernatural power but in a scientific context there’s nothing we can do to reliably test the existence of some unseen intelligent force acting on the world so we cannot consider it as part of a scientific debate.
I feel that like Archbishop Ussher we are not seeing the whole picture and that there is some aspect of this subject that we are unaware of. What that is and whether we will find it remains to be seen. I know it’s not very satisfactory calling on something unknown to solve a problem. But according to astrophysicists most of the Universe is dark energy and dark matter. They can’t tell us the nature of either of these substances and some scientists have suggested that they might not exist at all. So, where does that leave us on the question of whether life is common or rare in the universe of whether the Earth is unique?
My take on this is that the Earth is an unusual planet on which conditions suitable for the formation of life occurred very early on in its history. I will not be surprised if there is no life past or present on Mars or anywhere else in the Solar System but I hope I’m wrong. Basic single cell life probably exists elsewhere in the galaxy and complex multicellular life with the potential to built a technology is going to be relatively rare.
Life on another planet imagined by TheDigitalArtist on pixabay. https://pixabay.com/illustrations/space-modern-science-fiction-886058/
When writing science fiction, I have not hesitated to fill my fictional planets with life in various forms as required including an intelligent being that we might not easily recognise as intelligent but I’m not confident that there are as many life bearing planets out there as I would like there to be. I’m hoping that biologists will eventually explain exactly how life did come into existence. The answer must be out there somewhere because here we are.
In Part 2, I shall be looking at the various forms of life that have been included in science fiction including some of my own.
All images from pixabay.com