Amazing Oxygen-Key to Planetary Life
One of the best science books I read in 2009 was Life Ascending: The Ten Great Inventions of Evolution by biochemist Nick Lane.
Although I think I have a good basic understanding of fundamental biological processes, I didn’t find the book an easy read, frankly. This is no criticism of Lane’s writing. The biological processes he describes are incredibly complex and involved. Lane defines his terms and does a great job describing biological and biochemical processes, often using helpful analogies and metaphors.
Still, at a certain point of explanation, he can’t help but use a lot of advanced jargon and concepts from his field. Again, I don’t fault him for this. This is a problem any writer faces explaining the cutting-edge of science to non-scientists. After reading this book, I was convinced, if I wasn’t before, that the problems biologists and biochemists are trying to solve about DNA, evolution, and the origins of life and consciousness are every bit as deep and mystifying as those in advanced physics and cosmology.
Oh, by the way, what are the ten great “inventions” of evolution, according to Lane? (And no, by “invention” he’s not talking about so-called “intelligent design!” Read the book and see what he means.) His admittedly arbitrary, but well-reasoned choices are:
1 the origin of life
4 the complex cell
8 hot blood
Although I think the book will be a stretch for most popular science readers, such as myself, I found it well worth the effort. Even when I couldn’t follow the details, I found the sweep and scope of what biologists and biochemists have discovered through new technologies and groundbreaking research breath-taking and thought-provoking.
To give you an idea of how Lane ties ideas together to give you the big picture, here is one of my favorite passages from his chapter on photosynthesis. It’s all about a waste product—oxygen. Of course, we all know we need it to breathe, but here’s the bigger picture:
“Oxygen is the key to planetary life. No more than a waste produce to photosynthesis, oxygen really is the molecule that makes a world. It is let loose by photosynthesis so fast that it finally overwhelms the capacity of a planet to swallow it up. In the end, all the dust and all the iron in rocks, all the sulphur in the seas and methane in the air—anything that can be oxidized—is oxidized, and free oxygen pours into the air and oceans.
Once there, oxygen put a stop to the loss of water from the planet. Hydrogen, when released from water (by ultraviolet radiation from the Sun), inevitably bumps into more oxygen before it finds its way into outer space. Swifty, it reacts to form water again, which now rains back down from the heavens, drawing to a halt the loss of oceans. And when oxygen accumulates in the air, an ozone shield forms, ablating the searing intensity of ultraviolet rays, and making the world a more habitable place.
Oxygen doesn’t just rescue a planet’s life; it energises all life, and makes it big. Bacteria can do perfectly well without oxygen; they have unparalleled skill as electrochemistry, they are able to react together virtually all molecules to glean a little energy. But the sum total of energy that can be derived from fermentation, or by reacting two molecules like methane and sulphate together, is negligible in comparison with the power of oxygen respiration—literally, the burning up of food with oxygen, oxidizing it fully to carbon dioxide and water vapor. Nothing else provides the energy needful to fuel the demands of multicellular life….So a world without oxygen is microscopic, at least at the level of individual organisms.
Oxygen contributes to large size in other ways too. Think of a food chain. The top predators eat smaller animals, which might in turn eat insects, which eat smaller insects, which live on fungus and leaves. Five or six food levels in a food web are not uncommon. At each step energy is wasted, for no form of respiration is ever 100 per cent efficient. In fact, oxygen respiration is about 40 per cent efficent, while most other forms of respiration (using iron or sulphur instead of oxygen, for example) are leass than 10 per cent efficient.
This means that, without oxygen, the energy available dwindles to 1 per cent of the initial input in only two levels, whereas with oxygen it takes six levels to arrive at the same point. That in turn means that longer food chains are only feasible with oxygen respiration. The economy of the food chain means that predators can operate in an oxygenated world, but predation as a lifestyle just doesn’t pay without oxygen.
Predation escalates size, of course, driving arms races between predator and prey. Shells combat teeth, camouflage tricks the eye; and size intimidates both hunter and hunted. With oxygen, then, predation pays, and with predators size pays. So oxygen makes large organisms not just feasible but also probable.
…It’s striking that higher plants, too, need free oxygen to from their structural support, in the shape of immensely strong polymer lignin, which gives wood is flexible strength. Lignin is formed in a chemically haphazard way using free oxygen to form strong cross-links between chains. These are very difficult to break down, which is why wood is so strong and why it takes so long to rot. Eliminate lignin from trees—a trick that manufacturers of paper have tried, as they need to remove it laboriously from wood pulp to make paper—and the trees slump to the ground, unable to sustain their own weight even in the lightest breeze.
So without oxygen there would be no large animals or plant, no predation, no blue sky, perhaps no oceans, probably nothing but dust and bacteria. Oxygen is without a doubt the most precious waste imaginable….”
Nick Lane’s Life Ascending: The Ten Great Inventions of Evolution is a fascinating, if challenging read. If you want to expand your understanding of the origins of life on our “pale blue dot,” the only world we’ve ever known, this book is one you’ll want to read.
Here’s a link to the book on Amazon.com: