A while ago, I posted an article called Alien life, in which I asked the question whether people thought life might exist on any of the multitude of exoplanets being discovered. I have since learned some stuff I didn’t know before, which has altered my own views. Some of the information comes from a book called Rare Earth, and some of it from other research I am doing. I can’t in this space include all this stuff, but I will summarize the key points.
- On Earth, forms of bacteria and Archea (single celled life forms) have been found that live in super-hot (hotter than boiling water) environments, in rocks, in ice, in sulfur springs, deep under the Earth’s core, in the absence of light or oxygen, and so on. These “extremeophiles”, suggest that life could likely exist in many other environments other than the relatively Earth like one we know,
- On the other hand, animals require very special conditions, including oxygen, water, moderate temps, moderate pressure, and so on. Before you object that we can’t really know about what is possible, I should say that this conclusion is based on general principles of chemistry and physics.
- The first life appears on Earth in the fossil record almost 4 billion years ago. This single cell life form appears to have been DNA based, and able to do photosynthesis. It is possible that very little time elapsed between the cooling of the new born Earth and appearance of pretty sophisticated living cells. It is highly unlikely that spontaneous chemical evolution on Earth could explain the origin of terrestrial life in such a short period of time, and raises the long held hypothesis that life arrived on Earth on a comet or asteroid to a higher level of probability. Especially in light of point 1.
- The Earth is a very unusual planet in many ways, in relation to its size, shape, temperature, atmosphere, magnetic field, period and shape of rotation, degree of large object impacts, (because of the presence of nearby gas giants, Jupiter and Saturn), the position of its star (the Sun) in the Galaxy, the fact that its star is not a binary or higher star system, its geological history and structure, including plate tectonics, its stable but slightly variable climate, size of its moon, and a few other things, all of which turn out to be essential for the evolution of larger than microscopic, multicelled animals. In other words the Earth may be, even in a galaxy filled with millions of planets and moons, hundreds of thousands of which are likely to harbor simple life forms, the only place where animals, including conscious, intelligent ones, like us (or at least some of us) can exist.
So, this could mean that while we might actually find living microorganisms in lots of places, including Mars, Europa, and in many other solar systems, we will not find any other civilizations, aliens, or anything else with a nervous system, let alone a desire to conquer or communicate.