Oxygen

Summary

In this book Nick Lane explores the profound impact that the oxygen molecule had on the history of life and how it changed everything. He covers a lot of ground, how the energy that oxygen makes possible to harvest lead to multicellularity, how oxygen first arising lead to a massive extinction event, how the very minerals that we find today in the earths crust were permanently altered and how oxygen enabled life to go on land via the creation of an Ozone layer, that blocks the deadly high energy radiation of the sun. One could say that oxygen is the molecule that makes life work. Yet, somehow, it is toxic, borderline dangerous, because it helps things burn, but somehow life found a way to harness this destructive energy and turn it into something beautiful.

Oxygen is both vital and toxic. It's a matter of concentration as well as adaptation. Today's life is highly adapted to use oxygen, yet, if the percentage concentration of oxygen in the atmosphere were higher, we would have massive, unstoppable forest fires. Using oxygen in cellular metabolism also creates hyper agressive byproducts called ROS => reactive oxygen species, that are tearing through cellular machinery, destroying (almost) everything in their path.

In order to harness oxygen in metabolism, life needed to find ways to deal with this. That's why we have antioxidants, DNA repair mechanisms and a host of other adaptations that enable us to deal with the fallout of harnessing oxygen to generate vast amounts of energy. To this day though, organisms still deal with the consequences of this, including us. When we get older, the damage that ROS does, accumulates in cells leading to many of the detrimental effects that we associate with aging. This is known as the Free Radical Theory of Aging. The exact details of how this works are complicated and (largely) not perfectly understood yet though.

Without aerobic metabolism, multicellular, complex life would not exist. The energy requirements of animals are absurd, compared to those of single celled organisms and the only way to harness and utilize this much energy is through the use of oxygen. All the sophisticated machinery that complex multicellular bodies can have relies on oxygen. It lead to the Cambrian Explosion.

Key Ideas

Oxygens duality: high reactivity means oxygen can be both good and bad for life. But the dangerous tradeoff is worth it, because it enables all the cool complicated stuff animals can do. Metabolism revolves around oxygen and provides the energy necessary to have things like muscles, skeletons or brains. Yet oxygen is also responsible for the process of aging. Aging is the accumulation of the damaging effects of oxygen based metabolism and the free radicals it produces.

Great Oxygenation Event: Life altered the composition of the entire atmosphere by producing a lot of oxygen. This killed off many of the existing life forms that couldn't deal with these toxic levels. This also introduced Ozone into the top layer of the atmosphere (breakdown of O2 into 03 by collision with high energy particles), which made it possible for DNA based life to inhabit the land. Without oxygen there would be no life on land. Finally it kickstarted the evolution of complex life by providing the possibility to evolve more energy consuming strategies of living that revolve around oxygen.

It suffices to say, oxygen is one of the most important molecules that evolution has ever stumbled upon and is an integral part of life as we know it today, without it.