Earth Had Oxygen Much Earlier Than Thought

[Eugene]

Source: LiveScience

Earth Had Oxygen Much Earlier Than Thought

By Charles Q. Choi, LiveScience Contributor | September 25, 2013 01:11pm ET

Oxygen may have filled Earth's atmosphere hundreds of millions of years earlier than previously thought, suggesting that sunlight-dependent life akin to modern plants evolved very early in Earth's history, a new study finds.

The findings, detailed in the Sept. 26 issue of the journal Nature,have implications for extraterrestrial life as well, hinting that oxygen-generating life could arise very early in a planet's history and potentially suggesting even more worlds could be inhabited around the universe than previously thought, the study's authors said.

It was once widely assumed that oxygen levels remained low in the atmosphere for about the first 2 billion years of Earth's 4.5-billion-year history. Scientists thought the first time oxygen suffused the atmosphere for any major length of time was about 2.3 billion years ago in what is called the Great Oxidation Event. This jump in oxygen levels was almost certainly due to cyanobacteria — microbes that, like plants, photosynthesize and exhale oxygen.

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The new study pushes this boundary back even further, suggesting Earth's atmosphere became oxygenated about 3 billion years ago, more than 600 million years before the Great Oxidation Event. In turn, this suggests that something was around on the planet to put that oxygen in the atmosphere at this time.

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Read more: http://www.livescience.com/39938-earth-had-oxygen-earlier.html

[longship]

1. Interesting.

I heard an argument against the SETI searches by a physicist who apparently didn't like it.

His claim was that astronomers on a distant planet will likely have the ability to detect Earth's oxygen-rich atmosphere from great distances. (Astronomers here are close to being able to do just that. Google "James Webb Space Telescope".) An oxygen rich atmosphere is an almost certain indication of life. The thing is, only a few millions of years is required for a star to approach Sol in the galaxy. Any long lived civilization detecting Earth's oxygen atmosphere would want to investigate.

Of course, this is ridiculous as sending a spacecraft to Earth is a very expensive prospect whereas sending a radio signal is relatively cheap. But I found the argument interesting.

When the James Webb gets to its Lagrange point, we'll likely soon know about planets with life. At least one can hope.

We are not alone.

[muriel_volestrangler]

2. It indicates some oxygen, but not necessarily anything approaching present-day amounts

Here's the abstract of the letter to Nature:

It is widely assumed that atmospheric oxygen concentrations remained persistently low (less than 10?5 times present levels) for about the first 2 billion years of Earth’s history1. The first long-term oxygenation of the atmosphere is thought to have taken place around 2.3 billion years ago, during the Great Oxidation Event2, 3. Geochemical indications of transient atmospheric oxygenation, however, date back to 2.6–2.7 billion years ago4, 5, 6. Here we examine the distribution of chromium isotopes and redox-sensitive metals in the approximately 3-billion-year-old Nsuze palaeosol and in the near-contemporaneous Ijzermyn iron formation from the Pongola Supergroup, South Africa. We find extensive mobilization of redox-sensitive elements through oxidative weathering. Furthermore, using our data we compute a best minimum estimate for atmospheric oxygen concentrations at that time of 3?×?10?4 times present levels. Overall, our findings suggest that there were appreciable levels of atmospheric oxygen about 3 billion years ago, more than 600 million years before the Great Oxidation Event and some 300–400 million years earlier than previous indications for Earth surface oxygenation.

http://www.nature.com/nature/journal/v501/n7468/full/nature12426.html

A minimum of 3x10-4 times present levels.

[greiner3]

3. "A minimum of 3x10-4 times present levels."

What is the lowest, if any, level of O2 needed for life to arise?

[muriel_volestrangler]

4. It's thought that the first life didn't need any oxygen

Indeed, I think it's assumed most, if not all, life were 'obligate anaerobes' - organisms that are poisoned by oxygen. Some forms of life still are.

Oxygen is a very reactive element, and as well as reacting with inanimate materials such as iron, can also cause a lot of problems for living cells if they haven't evolved molecular defences against it.

But researchers have long been puzzled as to how the cyanobacteria could make all that oxygen without poisoning themselves. To avoid their DNA getting wrecked by a hydroxyl radical that naturally occurs in the production of oxygen, the cyanobacteria would have had to evolve protective enzymes. But how could natural selection have led the cyanobacteria to evolve these enzymes if the need for them didn’t even exist yet?

Now, two groups of researchers at the California Institute of Technology offer an explanation of how cyanobacteria could have avoided this seemingly hopeless contradiction. Reporting in the December 12 Proceedings of the National Academy of Sciences (PNAS) and available online this week, the groups demonstrate that ultraviolet light striking the surface of glacial ice can lead to the accumulation of frozen oxidants and the eventual release of molecular oxygen into the oceans and atmosphere. This trickle of poison could then drive the evolution of oxygen-protecting enzymes in a variety of microbes, including the cyanobacteria. According to Yuk Yung, a professor of planetary science, and Joe Kirschvink, the Van Wingen Professor of Geobiology, the UV-peroxide solution is “rather simple and elegant.”
...
Before there was any oxygen in Earth’s atmosphere or any UV screen, the glacial ice would have flowed downhill to the ocean, melted, and released trace amounts of peroxide directly into the sea water, where another type of chemical reaction converted the peroxide back into water and oxygen. This happened far away from the UV light that would kill organisms, but the oxygen was at such low levels that the cyanobacteria would have avoided oxygen poisoning.

“The ocean was a beautiful place for oxygen-protecting enzymes to evolve,” Kirschvink says. “And once those protective enzymes were in place, it paved the way for both oxygenic photosynthesis to evolve, and for aerobic respiration so that cells could actually breathe oxygen like we do.”

http://www.universetoday.com/1002/how-did-early-bacteria-survive-poisonous-oxygen/

(That's from 2006 - later research, like this new stuff, may have invalidated some of it. But it shows that, in general, oxygen is seen as a problem for early life, not a useful substance)

[Posteritatis]

5. None at all, for some kinds of life

The weird thing about oxygen, when you get down to it, is that it's really this horrible all-destroying poison of staggering power. It eats iron - eats iron! - makes things catch fire, and generally reacts to just about anything. The difference between oxygen and, say, elemental fluorine is one of degree rather than kind in that way. It's terrific for us, obviously, but it's jarring at times to sit there and think that, in order to live, we need a steady supply of a gas that turns old cars into piles of red powder.

The original oxygenation of the planet was a disaster to life that was present on it at the time; it would have nearly sterilized the planet (at least as far as their microscopic little minds would have been concerned), and would certainly have wrought a mass extinction against most anaerobic life.