Climate puzzle over origins of life on Earth

October 4, 2013, University of Manchester
Climate puzzle over origins of life on Earth

The mystery of why life on Earth evolved when it did has deepened with the publication of a new study in the latest edition of the journal Science.

Scientists at the CRPG-CNRS University of Lorraine, The University of Manchester and the Institut de Physique du Globe de Paris have ruled out a theory as to why the planet was warm enough to sustain the planet's earliest life forms when the Sun's energy was roughly three-quarters the strength it is today.

Life evolved on Earth during the Archean, between 3.8 and 2.4 billion years ago, but the weak Sun should have meant the planet was too cold for life to take hold at this time; scientists have therefore been trying to find an explanation for this conundrum, what is dubbed the 'faint, young Sun paradox'.

"During the Archean the received at the surface of the Earth was about 20 to 25 % lower than present," said study author, Dr Ray Burgess, from Manchester's School of Earth, Atmospheric and Environmental Sciences. "If the greenhouse gas composition of the atmosphere was comparable to current levels then the Earth should have been permanently glaciated but geological evidence suggests there were no global glaciations before the end of the Archean and that liquid water was widespread."

One explanation for the puzzle was that greenhouse gas levels – one of the regulators of the Earth's climate – were significantly higher during the Archean than they are today.

"To counter the effect of the weaker Sun, carbon dioxide concentrations in the Earth's atmosphere would need to have been 1,000 times higher than present," said lead author Professor Bernard Marty, from the CRPG-CNRS University of Lorraine. "However, ancient fossil soils – the best indicators of ancient carbon dioxide levels in the atmosphere – suggest only modest levels during the Archean. Other atmospheric greenhouse gases were also present, in particular ammonia and methane, but these gases are fragile and easily destroyed by ultraviolet solar radiation, so are unlikely to have had any effect."

But another climate-warming theory – one the team wanted to test – is that the amount of could have been higher in the ancient atmosphere, which would amplify the greenhouse effect of carbon dioxide and allow the Earth to remain ice-free.

The team analysed tiny samples of air trapped in water bubbles in quartz from a region of northern Australia that has extremely old and exceptionally well-preserved rocks.

"We measured the amount and isotopic abundances of nitrogen and argon in the ancient air," said Professor Marty. "Argon is a noble gas which, being chemically inert, is an ideal element to monitor atmospheric change. Using the nitrogen and argon measurements we were able to reconstruct the amount and isotope composition of the nitrogen dissolved in the water and, from that, the atmosphere that was once in equilibrium with the water."

The researchers found that the partial pressure of nitrogen in the Archean atmosphere was similar, possibly even slightly lower, than it is at present, ruling out nitrogen as one of the main contenders for solving the early climate puzzle.

Dr Burgess added: "The amount of nitrogen in the was too low to enhance the greenhouse effect of carbon dioxide sufficiently to warm the planet. However, our results did give a higher than expected pressure reading for – at odds with the estimates based on fossil soils – which could be high enough to counteract the effects of the faint young Sun and will require further investigation."

The paper is titled 'Nitrogen Isotopic Composition and Density of the Archean Atmosphere.'

Explore further: Ancient trapped water explains Earth's first ice age

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2.1 / 5 (17) Oct 04, 2013
Out of interest. How did we know the sun was 20-25% weaker back then?

Do we have direct evidence from Earth or it is just from looking at other suns that we extrapolated a 20-25% decrease in solar activity?

4.2 / 5 (5) Oct 04, 2013
It is nice if they have found more allowed CO2, but I think the tension is moving away from having global habitable conditions (non-snowball Earths) to remaining tension in early constraints on temperature. E.g. 2 consecutive papers where modern 3D climate models are used show that Earth would have been partially ice free, but they still don't predict the 35-50 degC waters @ ~ 3.1 - 3.0 Ga bp.

Also, since life clades with alkaline hydrothermal vents (Lane & Martin), global temperatures were less important. But again, if the Isua BIFs are accepted as trace fossils, it means Hadean climate > 3.8 Ga bp was globally more lenient. (And this recent dating of trace fossils is a possible nitpick to the idea that life evolved "between 3.8 and 2.4 billion years ago".)
4.2 / 5 (10) Oct 04, 2013
@ Doug_Huffman: Since this is a science news site, we should confine ourselves to actual science and its controversies, not to irrelevant social "manufactroversies".

Actually it is thanks to AGW and its social relevance that the climate models are now so good that they predict a habitable Archean climate, as expected.

Also, I wouldn't use the term "skeptical". Skeptic organizations accept science as the basis for their empirical skepticism. I don't think they would like social hijacking of their name. Rejecting climate science is anti-science, so it is more akin to buffoonery.
2.8 / 5 (6) Oct 04, 2013
"How did we know the sun was 20-25% weaker back then?" - tripelhelix.

Solar models.
4.2 / 5 (5) Oct 04, 2013
@triplehelix: AFAIK it is mostly a prediction from the Main sequence of stars (and hence models, see above).

"As non-fusing helium ash accumulates in the core of a main-sequence star, the reduction in the abundance of hydrogen per unit mass results in a gradual lowering of the fusion rate within that mass. Since it is the outflow of fusion-supplied energy that supports the higher layers of the star, the core is compressed, producing higher temperatures and pressures. Both factors increase the rate of fusion thus moving the equilibrium towards a smaller, denser, hotter core producing more energy whose increased outflow pushes the higher layers further out. Thus there is a steady increase in the luminosity and radius of the star over time.[17] For example, the luminosity of the early Sun was only about 70% of its current value.[39]"

[ http://en.wikiped...sequence ]

If you find any other evidence, perhaps geological traces of photoreaction rates, I would be interested!
1.7 / 5 (11) Oct 04, 2013
There would have been more radioactive elements several billion years ago. This would have been a source of extra internal heat then. Jupiter radiates away more heat than it receives from the sun even today.

Does Jupiter have an internal heat source - WikiAnswers ' Wiki Answers ' Categories ' Science ' Earth Sciences��ŽJupiter has an internal heat source as it emits 1.6 times a much energy as falls on it from the Sun.The main theory on the source of this heat that much of it is ...

Sorry the link did not show up.
1.4 / 5 (9) Oct 04, 2013
Wouldn't it be ironic if we eventually communicate with another civilized species and they don't know how life started either? lol.

Seriously though, since the surface of the Earth has basically re-surfaced itself since life formed, we are unlikely to find any direct evidence. That leaves us only theoretical, indirect methods.

If I had to guess, it seems improbable that there's only one path to life; only one set of acceptable conditions, etc. Perhaps we will have a better idea of what could have happened if we are ever able to fully synthesize life. I think we are really just poking around in the dark right now, since there's no way to either confirm or deny our initial assumptions. For example, what are the temperature constraints? Is there an atmospheric pressure constraint? Do you need certain building blocks already available in large abundance? Did it form under water or on the surface?

We really don't know what we are looking for yet. It's like a puzzle with most pieces gone
1.6 / 5 (14) Oct 04, 2013
If I had to guess, it seems improbable that there's only one path to life; only one set of acceptable conditions, etc

Quite the contrary I'd suspect. I think it's the reason we have absolutely zero evidence for any life anywhere else in a universe where IF the principle of mediocrity held (which it has with everything else we've "applied" it to) should be positively REPLETE with complex technological life.

I think the conditions are extraordinarily narrow and a fluke of truly cosmic proportions that life exists at all...
1.4 / 5 (11) Oct 04, 2013
Do the models account for residual heat from the impact of Theia with the Proto-Earth approximately 4.5 Gya (four and a half billion years) ago?
1.4 / 5 (11) Oct 04, 2013
Do the models account for residual heat from the impact of Theia with the Proto-Earth approximately 4.5 Gya (four and a half billion years) ago?
2.6 / 5 (5) Oct 04, 2013
"residual heat from the impact of Theia" - Tadchem

Yup. The temperature is of course measured, not theorized.

1.3 / 5 (13) Oct 04, 2013
Yet at the same time roughly Mars scientists are claiming it was much warmer than it is now. Makes one wonder.
not rated yet Oct 06, 2013
An interesting enigma to solve.

Hi Franklins! New "Waterripples" weekly nick.
2.6 / 5 (5) Oct 07, 2013

Quite the contrary I'd suspect. I think it's the reason we have absolutely zero evidence for any life anywhere else

Ah, but would we see it, could we see it?

I've said this before, so pardon the redundance.

If an alien spacecraft passed through our solar system at high speed, (even a very large spacecraft) we would have almost zero chance of spotting it. Even if there were hundreds of small probes zipping through at 75% C every year, we would probably not see any of them.

If such a spacecraft were broadcasting a simple broadcast television signal as it passed, the signal would be so doppler shifted as it passed that we wouldn't recognize it as a signal.

To say that we aren't surrounded by life, only because we haven't seen it, might be naive. Or maybe not.

That's an interesting point though. If we DO find that life is formed easily, then it'll be obvious that we must be surrounded by it, whether we see it or not?

It's all hypothetical now though.
1.8 / 5 (5) Oct 07, 2013
It's a bit exciting to think that some of these questions might be answered, at least partially, in our lifetimes. I think it's realistic to expect very high confidence answers regarding origins of life and extraterrestrial life within our children's lifetimes, if not in our lifetimes. We are right on the edge of so many discoveries; our technology is so close to being good enough to answer so many long standing 'big questions'.

Most people don't even understand how profound the origin of life question is. I think the average person probably paints it in religious versus non-religious terms, but doesn't realize what it means in regard to whether we are alone in the Universe or not.

As you pointed out, if life is exceedingly rare, then the Universe is one BIG lonely place.

I would be there's life everywhere, but they don't bother with us because there's no point. Resources and space are trivially abundant, so why disturb us and risk cross-contamination?

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