Enough oxygen long before animals rose

January 4, 2016

Oxygen is crucial for the existence of animals on Earth. But, an increase in oxygen did not apparently lead to the rise of the first animals. New research shows that 1.4 billion years ago there was enough oxygen for animals - and yet over 800 million years went by before the first animals appeared on Earth.

Animals evolved by about 600 million years ago, which was late in Earth's history. The late evolution of animals, and the fact that oxygen is central for animal respiration, has led to the widely promoted idea that animal evolution corresponded with a late a rise in atmospheric oxygen concentrations.

"But sufficient oxygen in itself does not seem to be enough for animals to rise. This is indicated by our studies", say postdoc Emma Hammarlund and Professor Don Canfield, Nordic Center for Earth Evolution, University of Southern Denmark.

Together with colleagues from the China National Petroleum Corporation and the University of Copenhagen, Hammarlund and Canfield have analyzed from the Xiamaling Formation in China. Their analyses reveal that a 1.4 billion years ago contained at least 4% of modern oxygen concentrations.

The new study is published in the journal Proceedings of the National Academy of Sciences.

Usually it is very difficult to precisely determine past oxygen concentrations. The new study, however, combines several approaches to break new ground in understanding oxygen concentrations 1.4 billion years ago.

The study uses trace metal distributions to show that the bottom waters where the Xiamaling Formation sediments deposited contain oxygen. The distribution of biomarkers, molecules derived from ancient organisms, demonstrate that waters of intermediate depth contain no oxygen. Therefore, the Xiamaling Formation deposited in an ancient oxygen-minimum zone, similar to (but also different) from those found off the present coasts of Chile and Peru.

With this backdrop, the researchers used a simple ocean model to estimate the minimum concentrations to atmospheric oxygen required to reproduce the distribution of water-column oxygen in the Xiamaling Formation.

"The water column had an oxygen concentration at least 4 % of present atmospheric levels (PAL). That should be sufficient for animals to exist and evolve", says Canfield.

"Having determined the lowest concentration of oxygen in the air almost one and a half billion years ago is unique", says Hammarlund, adding:

"Researchers know of simple animals, such as sponges and worms, that today are capable of managing with less than 4 % PAL, even much less."

"Sponges probably resemble some of the first animals on Earth. If they manage with less than 4 % today's oxygen levels, it is likely that the first animals could do with these concentrations or less", says Canfield.

The results differ from other studies and raise several questions, such as: Why then did animals rise so late in Earth's history?

"The sudden diversification of probably was a result of many factors. Maybe the rise had less to do with the animal revolution than we previously assumed", says Hammarlund.

Explore further: Ocean toxicity hampered the rapid evolution of complex life

More information: Sufficient oxygen for animal respiration 1,400 million years ago, www.pnas.org/cgi/doi/10.1073/pnas.1523449113

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2.5 / 5 (4) Jan 04, 2016
"Sponges probably resemble some of the first animals on Earth. If they manage with less than 4 % today's oxygen levels, it is likely that the first animals could do with these concentrations or less", says Canfield.

That's a faulty line of logic.

Present day organisms have had hundreds of millions of years to evolve to survive on less and less in order to fill all the niches. One would expect the first animals to require more oxygen - not less - as they hadn't the time to optimize the collection and use of it. They were most likely very bad at it to start.

The first organisms to breathe oxygen made the switch because oxygen is a poison to everyone else- kinda like extremophiles that live in boiling water because there's no competition there - so the oxygen breathing animals would logically evolve only after it became a sufficient competetive advantage, not simply when it first became available.
5 / 5 (1) Jan 05, 2016
The standard model here is, as I understand it, that oxygen, already used by the clades of eukaryotes that are stem clades to animals (such as choanoflagellates; https://en.wikipe...agellate ), sets a limit to multicellular behavior.

I.e. at low oxygen levels the size of the cellular aggregates (see the link) is limited by diffusion. It isn't known but suspected that the Ediacaran had a fauna (animals) that relied circulation outside for oxygen and all other nutrients, they were fractal ("frond like"). Sponges have a related behavior in that they set up cups with circulation inside.
5 / 5 (1) Jan 05, 2016

It is an interesting notion that oxygen, after its poisoning effects were overcome, was an unexploited resource. [It is still a poison to aerobic organisms, but they use an older set of enzymes to protect from O2 (OO) that evolved to protect from equally harmful NO.]

But an aerobic metabolism is very advantageous, especially in eukaryotes, it liberates much more energy. I don't think I have seen speculation that any delays were due to competition. Instead increasing oxygen levels lead to an explosion in diversity (a bothersome poison to some; a resource for others).

The geology (oxygen content) of the Boring Billion period is still controversial, as the article reflects. I thought the chromium isotope results [see the abstract] that I just heard of elsewhere would settle the issue. Evidently not yet.
5 / 5 (1) Jan 05, 2016
Your mention of "much more energy" reminded me of the Warburg effect, which is basically the fact that certain organisms continue to respire anaerobically under aerobic conditions. Why would they do so if they were missing out on a big energy payoff? The answer, at least according to this recent article, http://phys.org/n...ion.html , is research that measured "...the cost of synthesizing fermentation versus respiratory enzymes by using proteomic mass spectrometry and discovered that respiratory proteins are twice as expensive as fermentation proteins for the same rate of energy generation."
not rated yet Jan 09, 2016
"The water column had an oxygen concentration at least 4 % of present atmospheric levels (PAL). That should be sufficient for animals to exist and evolve", says Canfield.
The 800 millions years gap before the existence and evolution of the animals can be easily explained.I mean 1.4 billions years ago there was not only oxygen but toxic gases such as hydrogen sulfide which was decomposed into sulfate stones and water.

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