Oxygen's challenge to early life

Oxygen's challenge to early life
Researcher Benjamin Gill near the top of a stratigraphic section at Lawsons Cove, Utah. Credit: Steve Bates.

The conventional view of the history of the Earth is that the oceans became oxygen-rich to approximately the degree they are today in the Late Ediacaran Period (about 600 million years ago) after staying relatively oxygen-poor for the preceding four billion years. But biogeochemists at the University of California, Riverside have found evidence that shows that the ocean went back to being "anoxic" or oxygen-poor around 499 million years ago, soon after the first appearance of animals on the planet, and remained anoxic for 2-4 million years. What's more, the researchers suggest that such anoxic conditions may have been commonplace over a much broader interval of time, with their data capturing a particularly good example.

The researchers argue that such fluctuation in the ocean's oxygenation state is the most likely explanation for what drove the rapid evolutionary turnover famously recognized in the of the (540 to 488 million years ago).

They report in the Jan. 6 issue of Nature that the transition from a generally oxygen-rich ocean during the Cambrian to the fully oxygenated ocean we have today was not a simple turn of the switch, as has been widely accepted until now.

"Our research shows the ocean fluctuated between oxygenation states 499 million years ago," said co-author Timothy Lyons, a professor of , whose lab led the research, "and such fluctuations played a major, perhaps dominant, role in shaping the early evolution of animals on the planet by driving extinction and clearing the way for new organisms to take their place."

Oxygen is a staple for animal survival, but not for the many bacteria that thrive in and even demand life without oxygen.

Understanding how the environment changed over the course of Earth's history can clue scientists to how exactly life evolved and flourished during the critical, very early stages of .

"Life and the environment in which it lives are intimately linked," said Benjamin Gill, the first author of the research paper, who worked in Lyons's lab as a graduate student. Gill explained that when the ocean's oxygenation states changed rapidly in Earth's history, some organisms were not able to cope. Further oceanic oxygen affects cycles of other biologically important elements such as iron, phosphorus and nitrogen.

"Disruption of these cycles is another way to drive biological crises," he said. "Thus both directly and indirectly a switch to an oxygen-poor state of the ocean can cause major of species."

The researchers are now working on finding an explanation for why the oceans became oxygen-poor about 499 million years ago.

"What we have found so far is evidence that it happened," Gill said. "We have the 'effect,' but not the 'cause.' The oxygen-poor state persisted for 2-4 million years, likely until the enhanced burial of organic matter, originally derived from oxygen-producing photosynthesis, resulted in the accumulation of more oxygen in the atmosphere and ocean. As a kind of negative feedback, the abundant burial of organic material facilitated by anoxia may have bounced the ocean to a more oxygen-rich state."

Gill stressed that understanding past events in Earth's distant history can help refine our view of changes happening on the planet presently.

"Today, some sections of the world's oceans are becoming oxygen-poor – the Chesapeake Bay and the so-called 'dead zone' in the Gulf of Mexico are just two examples," he said. "We know the Earth went through similar scenarios in the past. Understanding the ancient causes and consequences can provide essential clues to what the future has in store for our ocean."

In the study, Lyons, Gill and their team examined the carbon, sulfur and molybdenum contents of rocks they collected from localities in the United States, Sweden, and Australia. Combined, these analyses allowed the team to infer the amount of oxygen present in the ocean at the time the limestones and shales were deposited. By looking at successive rock layers, they were able to compile the biogeochemical history of the ocean.

Lyons and Gill were joined in the research by Seth A. Young of Indiana University, Bloomington; Lee R. Kump of Penn State University; Andrew H. Knoll of Harvard University; and Matthew R. Saltzman of Ohio State University. Currently, Gill is a postdoctoral researcher at Harvard University.

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Jan 06, 2011
I am looking forward to seeing a chart of oxygenation levels over time combined with species diversity in a almost continuous chart from then till now. Couple that with continental location and atmospheric pressure and global temperature plus a few other things.

Jan 06, 2011
at the time the limestones and shales were deposited. By looking at successive rock layers, they were able to compile the biogeochemical history of the ocean

Herein lies the weakness of this research - the assumption that limestone had formed at a uniform rate the same as it would do today. If at any stage the limestone formed rapidly then this research falls on its ears.

There is indeed such a period during which limestone could have formed at much greater rates - during a period of tremendous upheaval caused by the breaking up of the earth's crust in vital places to allow the "springs of the deep" to gush forth water for the great global flood.
At the same time there would be a tremendous amount of organic material swept along into places of water accumulation, not necessarily just the oceans although that would also be one place of gathering.
Such a global flood could then result in signs of oxygen fluctuations AND it would also account for the "Cambrian" explosion.

Jan 06, 2011
the breaking up of the earth's crust in vital places to allow the "springs of the deep" to gush forth water for the great global flood.

Please provide evidence that the bible is anything more than the collected stories of bored stone-age shepherds. Please provide evidence of the existance of a god or gods -- any gods will do. Until you establish some credibility for the basic foundation of your superstitious beliefs, all this "founts of the deep" nonsense is just futile application of band-aids to a set of fairy tales.

Jan 06, 2011
The problem, Kevin, is that the Cambrian explosion occurred some 530 million years BEFORE the flood...

Jan 06, 2011
Sorry, I should expand a little on my previous post. Creationists as a whole seem to think that all they have to do is poke some holes in evolutionary theory and voila -- creationism wins! Unfortunately, it doesn't work like that. This isn't a two-horse race. Assuming for a second that creationists were actually able to come up with some valid objections to evolutionary theory (no, kevin, you haven't yet), it would cast doubt on evolution as a specific theory, but wouldn't do anything to eliminate the possibility of a scientific, non-supernatural explanation. Scientists would simply adapt evolution or come up with a new theory that explained the facts better. That's the way science works, and it's the way it's *supposed* to work. So, it'd be back to square one for the creationists.
In order to make some actual headway, the creationists would have to show that not only is evolution invalid, but NO scientific theory is possible EVEN IN PRINCIPLE.

Jan 06, 2011
That sounds like a pretty tall order, but if you're going to try to prove your belief by process of elimination, that's what you're stuck with. The trouble is, you're not there yet. Now, the creationists have to eliminate non-scientific but non-theistic possible explanations, like the idea that we're living in a computer simulation or some such.
So, if they accomplish this second herculean task, have they won? Nope. We still have the possibility that there's some explanation that we simply haven't thought of, that doesn't involve magical sky fairies. Well, ok, let's assume they manage to discount that. Won yet? Nope. The trouble is that there are umpteen different creation myths involving different belief systems. Now the creationists have to find ways to eliminate all these rivals.

Jan 06, 2011
This will be, if it's possible, even MORE difficult because all these competitors enjoy the same ability to dismiss reason and logic, and the same total lack of need for comfirming evidence as does creationism. So, creationists have eliminated all rivals now. Have they proven their case? Nope. We still have the possibility that there's some other version of a deity or deities that don't currently have a following.
Point is, at some point you're going to have to present some valid POSITIVE proof for the christian version of the magical sky fairy. So far, he's failed absolutely every logical and evidentiary test, and the bible isn't fairing much better, since all historological and archeological evidence indicates that it really is just a set of collected legends (old testament) and politically manufucatured tales (new testament).

Jan 06, 2011
This, by the way, is why people like Strobels aren't convincing. They pretend to be scientists who have scientifically decided that creationism is The Answer, but they've skipped 99% of the questions that a real, competent scientist would deal with first. This does nothing but illustrate their pre-existing bias.

Anyway, Kevin, QC, and others -- good luck to you. You're talking trash like you're about to win the Stanley Cup and you haven't even made the pee-wee midget league yet.

Jan 06, 2011

Even though limestone deposition is not always constant, so far as sedimentary limestone is concerned, in many deposits the layers in the stone can be seen. Under the microscope many of these layers can clearly be resolved to be layers of fossils of the kinds made by organisms that make shells.

In many of these, the individual layers can be counted. A young earth cannot account for all the layers that have been observed in such limestone deposits and formations.

Likewise, in studies such as the above, the individual layers can be tested for composition and can be relatively dated, plus or minus some more or less small degree of years.

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