Sunday, 25 March 2018
The Many Events Without Which We Wouldn’t Be Here To Talk About Them
In the course of evolution, there have been many times when the future existence of my brain as I write these lines and yours as you read them has hung by the slenderest thread. Without the events, many of them quite unlikely, that occurred at these times, we would not be here today to speculate about their nature (or at least not in our current form).
We have all heard about the extinction of the dinosaurs, about 66 million years ago. After having ruled over practically every ecosystem on Earth for tens of millions of years, the dinosaurs disappeared suddenly (as measured on the geological time scale, of course), after an immense meteorite collided with the Earth, resulting in a nuclear winter. (Recent research suggests that intense volcanic activity at the same time probably contributed to this nuclear winter as well.) In the aftermath, small mammals that had previously led a somewhat insignificant existence were able to prosper in the ecological niches vacated by the dinosaurs. Thus an entirely fortuitous event is part of the reason that mammals, including the primate family to which we belong, exist in their present form.
But the impact of that meteorite isn’t the only event that seems to have been crucial to our current existence. An article that appeared in 2016, and whose title I have always loved (“The aliens are silent because they’re dead”), states that the universe is probably full of planets that are habitable: neither too close nor too far from their star for water to exist on their surface in liquid form, which is a prerequisite for the development of life as we know it. But this article also states that while it is highly likely that some primitive forms of life have developed on these planets, it seems increasingly unlikely that these life forms can evolve beyond a certain stage, because the unstable environments in which they have evolved have made them so fragile.
Little do we realize how many unbelievable random events had to take place on Earth for life here to evolve beyond these early stages. And these events begin with another collision—the one that, according to the most heavily debated hypothesis at present, resulted in the formation of the Earth’s largest natural satellite, the Moon. Somewhat like a gyroscope, the Moon has a stabilizing effect on the rotation of the Earth’s axis, resulting in a regularity in the seasons without which life on our planet would be vulnerable to many more risks. Likewise, until modern times, a subtle equilibrium regulated the composition of the gases in the Earth’s atmosphere, including the proportion of carbon dioxide. Now that industrialization has upset this balance, we see how greenhouse gas effects and global warming are threatening life on Earth as we know it.
Many other events have been crucial to the evolution of human beings. I will end this post with just a few examples: the formation of lipid bilayer cell membranes; the emergence of photosynthesis, leading in turn to the emergence of oxygen in the atmosphere; the emergence of sexual reproduction; and the emergence of multicellular organisms.
From the Simple to the Complex | No comments
