In my post last week on Hawking’s claim that science showed that God is unnecessary to explain creation, I made a comment on life:
In addition, Hawking also claims that the universe is “just right” to create living things like us. Instead, I argue that life is rare (first look around our neighbors in our solar system, then look at the history of life on earth and everything that had to happen for multicellular organisms to thrive) and that it is complex, intelligent Life is much less often silent. If anything, intelligent life is a coincidence in our universe, the exception rather than the rule.
A large number of readers responded, essentially claiming that I have no observational basis for such allegations. Today I want to come back to the subject that is not only of great importance – Are we alone? – but also shows how science works by carefully analyzing the available data and testing hypotheses.
First, notice that my comment was not about life, it was about complex, intelligent life. There is a big difference! Simple life can be abundant. Indeed, what we know about the only sample of life – planet Earth – shows that life finds its way under the right conditions. The earth was formed about 4.5 billion years ago from the same nebula from which the sun and all other planets in the solar system emerged. For the first 600 or 700 million years, the earth was a veritable hell, constantly bombarded by the debris that was left over from the formation of the planets and their moons. Life was impossible under these conditions. The earth did not have a solid crust and its surface would constantly melt due to the energy of the violent impacts.
About 3.9 billion years ago it became relatively quiet. Simple chemicals reacted and 3.5 billion years ago the first simple life forms swam in the flat ancient oceans of the earth. Some scientists would claim that there were signs of life as early as 3.8 billion years ago, but these results remain controversial. Even if we take the time 3.5 billion years ago as a starting point, we can find that life on earth formed within a few hundred million years, which is quite rapid on a planetary scale. So simple life can be pretty easy to assemble. What about complex life?
These were prokaryotes, primitive cells with exposed genetic material. More modern cells, like the eukaryotes we are made of, have the genetic material protected in sacks (DNA is in a nucleus). The prokaryotes ruled for about two billion years. Only then (numbers are rounded up here) did eukaryotic cells appear. As I discussed on another blog about sponges and creationism, spongy multicellular creatures didn’t appear until about 500 to 700 million years ago, either a few hundred million years ago.
That is, for about three billion years, life on earth existed only in the form of unicellular organisms.
The transition from unicellular to multicellular life forms remains unclear. Given what we know from natural selection, colonies of cells may have found it beneficial to congregate – united we win! – and function as a whole being. Or the one ate the other and formed a common being. However, it is clear that when we study the history of life on earth, we cannot separate it from the history of the earth itself. As a planet, the earth developed along with life. For example, the unicellular blue-green algae that populated Earth’s primitive oceans discovered photosynthesis (accidentally, of course), the ability to use the sun’s light to produce the energy they needed to survive. In doing so, they emitted oxygen, a gas that did not exist in the primitive atmosphere of the earth for about 2 billion years. It was this excess of oxygen that enabled more efficient metabolic pathways that eventually led to more complex life forms.
We are literally here because our distant unicellular ancestors learned to exhale oxygen.
So when we think about the existence of complex multicellular life in the cosmos, we have to take into account the conditions favorable for complex life not only to form, but to survive for a long time. It’s not just about liquid water and the right chemicals. (These are a must, of course.) The planet must have a stable orbit and relatively stable temperatures. In the case of Earth, the reason we have four seasons and temperatures that don’t change like crazy is because we have a big moon. The moon stabilizes the inclination of the earth (the earth is like an inclined top with an inclination of 23.5 degrees from the vertical) and enables stable seasons and liquid water for billions of years. Had the moon been brighter, the earth’s axis would wobble randomly, oceans could freeze for long periods of time, and complex life would be very difficult to survive.
The earth also has two very important “blankets” that protect life from the evil and deadly radiation that constantly rains from the sky. The earth’s magnetic field funnels electrically charged particles coming from the sun into the poles. Sometimes we see them as northern lights in high latitudes. In addition, the ozone layer protects us from the unpleasant UV radiation from the sun. Living near a star is not a picnic.
Some of these arguments were masterfully developed in the 2000 book Rare Earth by Peter Ward and Donald Brownlee. There are other arguments that we cannot go into. In my last book, A Tear at the Edge of Creation, I updated their arguments and put them in the context of what we know today.
After all, the jump from multicellular to complex multicellular and intelligent life is also a coincidence. Just think that intelligence came into being only recently, about 3.5 billion years after life came into being. It is common to think that intelligence and even complexity are a natural consequence of evolution, that is, if there is life, give it enough time and it will become intelligent.
Natural selection does not tell us that. Everything that is important to life is well adapted to the changing planetary environment. (And by the way, this is only possible because genetic reproduction allows mutations. If it had been perfect, life would fail.) Think of the stupid and terrifying dinosaurs who were happy here for 150 million years. No intelligence there, just good adaptation.
Given the enormous number of other planets and moons in the galaxy (and in the hundreds of billions of other galaxies!) And the fact that the laws of chemistry and physics apply throughout the cosmos, life certainly shouldn’t be an earthly phenomenon. But whatever life forms exist out there, given what we know about how life evolved here on earth and the many conditions that come into play to sustain complex life, it is a huge leap to assume that complex life is just as common. Smart life even more. I could also take advantage of the fact that we were not visited by aliens and explore Fermi’s Paradox, but I’ll leave that for another day. But even if there are other intelligent life forms in the galaxy and we cannot prove or rule this out with the evidence available, the reality is that for practical reasons we are alone and likely will be for the foreseeable future.
The mess we make is the mess we make.
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