"Which came first: complex life or high atmospheric oxygen?" Topic

"We and all other animals wouldn't be here today if our planet didn't have a lot of oxygen in its atmosphere and oceans. But how crucial were high oxygen levels to the transition from simple, single-celled life forms to the complexity we see today?

A study by UC Berkeley geochemists presents new evidence that high levels of oxygen were not critical to the origin of animals…."
Main page
link

Amicalement
Armand

The chicken, of course.

Dan

But roughly 2.45 billion years ago, the isotopic ratio of sulfur transformed, indicating that for the first time oxygen was becoming a significant component of Earth's atmosphere, according to a 2000 paper in Science.

link

And the first oxygen started showing up in the atmosphere (in small amounts) even a billion years earlier. Probably due to oxygen producing bacteria and archaea.

link

The chicken, of course.

Actually, the egg came first.

(smile)

Amicalement
Armand

A chicken is a egg's way of making more eggs.

Actually, the egg came first

Dinosaurs came from egg, and chickens evolved from dinos, so the egg wins.

(Although I assume T-Rex would taste more like Canada Geese and other migratory birds than chicken due to the extra exercise …)

Mmmmm…….T-Rex pâté.

And the dino egg came from the amphibian egg which came from the fish eggs.
So the egg beat the chicken by some 500-600 million years.

Getting back to the original link.

It was 1977 when I took second year microbiology as an undergraduate. I'm pretty sure that everything in the link above was taught to me at that time, 4 decades ago. We have since discovered that prokaryotes are divided into regular bacteria and archaea. That is new. Also many new species have been discovered and reclassified, especially with regard to early oxygen producing Cyanobacteria. But the general gist of the story is the same.

I remember the ideas that small primitive microorganisms began a genocidal chemical warfare battle to help terraform the planet to their requirements. Of course, none of this was due to direct intent. The bacteria, archaea (and later photosynthetic microorganisms) were just trying to reproduce and survive. Much like all life today. And the creatures that expired oxygen "poisoned" the planet by slowly increasing the oxygen content of, first the atmosphere and then, the oceans. The result was a planet that allowed for the evolution of the first eukaryotic organisms, about 2.7 bya. The efficiency of photosynthetic eukaryotes started pumping more O2 into the air, giving us the results, as explained in the link above, at 2.5-2.3 bya. This paved the way for larger more complex multicellular animals and plants to develop, including us.

Nice to see what I was taught so long ago seems to have been corroborated over the decades.

Of course the spread of multicellular life over the planet did not depend on oxygen in the atmosphere. Intelligent life could have evolved from the original atmosphere of hydrogen gas, water vapour, methane, CO2, etc.

Of course, the animal and plant life that would have evolved in that environment would now have a totally different form of respiration and metabolism. We might be breathing in methane and breathing out…..who knows? It's possible that the existence of a very reactive chemical, like oxygen, may have caused us to have a faster metabolic rate. So large intelligent animals in a non-oxygen heavy environment may be very sluggish in comparison to us. But that's just speculation. We'd have to visit one of those many planets we keep discovering to fully know.