Earlier this summer, I noted that I was reading Oxygen, The Molecule that Made the World. In fact, I finished that book before beginning my fall reading challenge. For some reason, I never posted a review. Eh, I blame the blackout.
Anyway, Oxygen is an extremely interesting book that delivers on its subtitle. The story begins four billion years in the past. Earth is an unremarkable rock covered in a fog of nitrogen, carbon dioxide, water vapor, and traces of other elements. All of these were contributed by volcanic gases. Oxygen only existed when ultraviolet light interacted with molecules of water vapor, splitting the hydrogen from the oxygen. The hydrogen would float off into space, and the oxygen would oxidize iron-rich rocks on the surface.
Earth would have ended up just like Mars, or even Venus, if not for one important development: LUCA, the Last Universal Common Ancestor. This single-celled organism, living 3.8 billion years ago, evolved a defense against the oxygen molecules that infested the shallow wasters where it lived. From that defense mechanism, evolved the process of photosynthesis. Oxygen began to fill the ocean.
Prior to photosynthesis, the oceans were a strange place, filled with dissolved iron. Anoxic bacteria called it home and fermented happily away. A billion years later, rising oxygen levels precipitated out the last of the iron, ending the age of the fermenters, but beginning the age of multicellular organisms, made possible by mitochondria.
Mitochondria are structures within cells that generate energy by performing the acts of chemistry collectively referred to as respiration. Mitochondria are thought to once have been a species of bacteria that developed a symbiotic relationship with single-celled eukaryotes, from which descended all plants and animals.
This symbiotic relationship, claims the author, is the very reason that two sexes are necessary. It is also responsible for some of the ill effects of aging. The explanation for this is that mitochondria wear out over time, and leak oxidized compounds into the host cells. The host cells can be badly damaged by this, or can enter “attack mode” and begin releasing defensive chemicals, or both.
To prevent new organisms from being “born old” with leaky mitochondria, egg cells are filled with pristine mitochondria early in a female’s life. The eggs then go dormant until fertilized.
The book goes into much, much more detail on these topics and many others that I haven’t even mentioned. After reading it, the fact that life exists at all is a wonder.