Oxygen's Impact on Evolution

Did a rise in oxygen levels in the atmosphere lead to the rise of complex life forms? The question doesn’t make sense at first. We know life adapts to whatever is available. By that token, oxygen levels can at most be the backdrop for however life evolved, but surely they cannot be called a causative factor…

 

In case of oxygen though, things are very different, writes Nick Lane in his book named (what else?) Oxygen:

“The most obvious basis for a causal link is energy production.”

Huh?

“Oxygen releases more energy from food than do sulphur, nitrogen or oxygen compounds acting as oxidants… The length of any food chain is determined by the amount of energy lost from one level of the chain to the next.”

 

Without oxygen, that efficiency is less than 10%. Put differently, it means each step of the chain gets only 10% of the previous step. Here is the key point:

“Below a 1% threshold, there is not enough energy available to eke out a living.”

Do the maths, and you see that food chains can’t exist in the absence of oxygen:

“(Life during low oxygen levels would) compete with each other for scarce resources, rather than ‘eating’ each other.”

 

But once the oxygen level in the atmosphere went up, respiration as the way to extract energy from food becomes possible. And the energy efficiency of oxygen based respiration is 40% at each step. Do the maths, and up to 6 levels in a food chain are now sustainable:

“Suddenly carnivorous food chains pay and the predator is born.”

 

The advent of the carnivore then sets off the next set of events in the complexity of life forms. How?

“Predation is a powerful stimulus to weight gain in both predators and prey, either to eat larger prey or to avoid being eaten.”

Which in turn creates other evolutionary pressures:

“Large size requires structural support.”

And those structural elements have to be built using what’s available:

“The two most important structural components of plants and animals, lignin and collagen, require oxygen for their synthesis.”

 

Oh, and one last thing about the effect of rising oxygen levels on life. Some of that oxygen formed the ozone layer:

“Ozone is good at absorbing ultraviolet rays, so once a thick ozone layer builds up, the penetration of damaging ultraviolet rays into the lower atmosphere is cut by a factor of 30 or more.”

 

Who’d have thought one molecule would have such a big impact on life on earth?

Comments

Post a Comment

Popular posts from this blog

Student of the Year

Image
As a toddler, my daughter loved Alia Bhatt’s songs, esp. the ones from Student of the Year . (That movie did have many good songs and well-choreographed dances). Fast forward to present day, when she is 12 yo. She rarely watches Hindi movies now, but one of the few ones she likes of late, Raja aur Rani ki Prem Kahani has, yes, Alia Bhatt.   If I had any hopes that there was anything to be read in the name of her toddler-time favorite ( Student of the Year ), they have been dashed. Our conversations come exam time are perfectly captured by this photo and its caption: In fact, the pic below captures how she and I look at her answer sheets – me intently, she with an expression of “It’s over, so why are you even looking at it?”   Of late, we pull her leg and tell her that she isn’t showing any signs of academic prowess, she’d better find a rich guy to marry. Some time later, she showed us this meme on the Internet: “Me No Study, Me No Care Me Go Marry Millionaire If He Die
Read more

The Retort of the "Luxury Person"

Image
Coming up with biting and witty retorts. It’s something we dream of, but rarely manage to pull off. Worse, the more we stew over the offending remark, the more likely we are to come up with that dream retort, as Calvin ruefully points out: During our last holiday at the Taj Resort, seeing my wife carrying towels to our poolside chairs, one of the kids there mistook her for a member of the staff and asked for a towel. When my wife narrated this to us, I did not imagine that my 8 yo daughter would come up with her own retort. But a day later, my daughter recapped the incident, an incident that didn’t even involve her in the first place , and said, “You know what I’d have told that kid who asked for the towel?”. And without waiting for an answer, she told us anyway: “I don’t work here. I too am a luxury person who is living at this resort. Go get your own towel.” We were highly amused by the phrase she had coined: “luxury person”. It certainly captures the kind of holid
Read more

Animal Senses #7: Touch and Remote Touch

Instinctively, we think touch is based on contact. Not entirely true, explains Ed Yong in Immense World – there’s a more important aspect than contact: “These incredible feats are possible through movement. If you rest a fingertip upon a surface, you can get only a limited idea of its features. But as soon you’re allowed to move, everything changes. Hardness becomes apparent with a press. Textures resolve at a stroke.” As you run your fingers over a surface, they hit the tiny peaks and troughs and set off vibrations in the mechanoreceptors at their tips.   At the tip of its snout, the star-nosed mole has many pairs of hairless appendages. It uses them to touch things around itself. Alive or dead? Food or ignore? It does these movements at an insane speed. In the time it takes to blink our eyes, the star-nosed mole can probe, identify and swallow its food. “Light may be the fastest thing in the universe, but light sensors have their limits, and the star-nosed mole’s sense of
Read more