CU: Early Earth Haze Likely Provided Ultraviolet Shield

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CU: Early Earth Haze Likely Provided Ultraviolet Shield

Post by bystander » Sat Jun 05, 2010 6:47 am

Early Earth Haze Likely Provided Ultraviolet Shield for Planet
University of Colorado at Boulder - 03 June 2010
A new study shows a thick organic haze that enshrouded early Earth several billion years ago may have been similar to the haze now hovering above Saturn's largest moon, Titan, and would have protected primordial life on the planet from the damaging effects of ultraviolet radiation.

The University of Colorado at Boulder scientists believe the haze was made up primarily of methane and nitrogen chemical byproducts created by reactions with light, said CU-Boulder doctoral student Eric Wolf, lead study author. Not only would the haze have shielded early Earth from UV light, it would have allowed gases like ammonia to build up, causing greenhouse warming and perhaps helped to prevent the planet from freezing over.

The researchers determined the haze of hydrocarbon aerosols was probably made up of fluffy, microscopic particles shaped somewhat like cottonwood tree seeds that would have blocked UV but allowed visible light through to Earth's surface, Wolf said.

Prior to the new study, the prevailing scientific view was that the atmosphere of Earth some 3 billion years ago was primarily made up of nitrogen gas with lesser amounts of carbon dioxide, methane, hydrogen and water vapor, said Wolf. "Since climate models show early Earth could not have been warmed by atmospheric carbon dioxide alone because of its low levels, other greenhouse gases must have been involved. We think the most logical explanation is methane, which may have been pumped into the atmosphere by early life that was metabolizing it."
Fractal haze may have warmed the early Earth
New Scientist - 03 June 2010
A haze of fluffy fractal-shaped particles may have helped protect early life from harmful ultraviolet radiation, a new study suggests. The aerosols could help resolve a long-standing puzzle about how the early Earth stayed warm.

Billions of years ago, the sun emitted up to 30 per cent less light than it does today. That should have made the early Earth too cold to maintain liquid water on the surface until about 2 billion years ago. But geological studies of banded iron formations and other materials that can form in water suggest liquid water pooled on the surface much earlier.
Early Faint Sun Paradox Explained?
Universe Today - 03 June 2010
Models of the Sun’s evolution indicate it was as much as 30 percent less luminous during Earth’s early history than it is now. But, somehow the surface of the planet was warm enough for primordial life to emerge. A new study and a look at Saturn's moon Titan has provided clues for how the Sun could have kept the early Earth warm enough. Scientists say a thick organic haze that enshrouded early Earth several billion years ago may have been similar to the haze that covers Titan and would have protected emerging life on the planet from the damaging effects of ultraviolet radiation, while warming the planet, as well.
...
This new study will likely re-ignite interest in a controversial experiment by scientists Stanley Miller and Harold Urey in the 1950s in which methane, ammonia, nitrogen and water were combined in a test tube. After Miller and Urey ran an electrical current through the mixture to simulate the effects of lightning or powerful UV radiation, the result was the creation of a small pool of amino acids — the building blocks of life.
Countering the Early Faint Sun Fractal Organic Hazes Provided an Ultraviolet Shield for Early Earth No climate paradox under the faint early Sun

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Re: CU: Early Earth Haze Likely Provided Ultraviolet Shield

Post by owlice » Sat Jun 05, 2010 7:11 am

"fluffy" <-- I like this!
A closed mouth gathers no foot.

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Re: CU: Early Earth Haze Likely Provided Ultraviolet Shield

Post by bystander » Sat Jun 05, 2010 7:35 am

Life May Have Formed on Earth Thanks to a Lush, Enveloping Haze
Discover Blogs | 80beats | 03 June 2010
You can't rise from the primordial ooze if that ooze is frozen. But about three billion years ago the sun was around thirty percent dimmer, meaning our planet should have been a snowball. The puzzle has haunted scientists for decades, but a study in Science has a new answer: It argues that a dense cloud of "fractal haze" enveloped the Earth.

Old Theories

This isn't the first attempt to solve the early Earth conundrum. Carl Sagan, for one, had a few ideas. First, in 1972, he speculated that the atmosphere had ammonia which could trap heat, but later work showed that the Sun's ultraviolet radiation would have broken that ammonia down. In 1996 he tried again, saying that Earth might have had a thick haze, perhaps a nitrogen-methane mix, that blocked the ultraviolet but let in enough of the Sun's then-meager rays to warm the planet. Unfortunately, that too was a no go:
Early models assumed the haze particles were spheres, and that when individual particles collided, they globbed together to make bigger spheres. These spheres blocked visible light as well as ultraviolet light, and left the Earth’s surface even colder.

“It basically led us to a dead end where we couldn’t have a warm early Earth,” said Eric Wolf, a graduate student in atmospheric sciences at the University of Colorado at Boulder and the first author of the new study. [Wired]

This Theory

The perfect haze was not too sparse (since it needed to provide some UV-protection for developing life), and not too dense (because then the planet would have been dark and cold). Just right, the new study suspects, might have been hydro-carbon clouds of what the study's authors call fractal haze. Unlike the spherical haze particles, fractal haze is made of long chains of particles stuck together.
The end result of this arrangement, dubbed a fractal size distribution, would be an aerosol haze opaque enough to block the shortwave ultraviolet radiation that would have hindered or prevented life from arising. At the same time, it would have proven transparent enough in longer, visible wavelengths to let them keep the atmosphere warm and the planet wet enough for life to emerge.

"It's surprising that molecules with complex shapes could make such a difference," said researcher Eric Wolf. [Space.com]

This theory also allows Sagan's ammonia, protected from the UV, to exist in the atmosphere. The famous Miller-Urey experiment -- in which scientists sparked what they believed comprised the earth's early atmosphere and made amino acids, life's building blocks -- assumed that the young planet had ammonia to work with.

Alternate Theories?

But in April, scientists proposed another answer: that the young earth had smaller land masses and so reflected fewer of the Sun's rays, absorbing more heat. But it's possible that the theories can work together.
Rather than being an alternate explanation to last month’s theory about how Earth stayed warm under a faint young sun, the newly proposed haze layer may actually be a complement to it, says Wolf. Researchers who conducted that study didn’t include a haze layer, which probably would have helped keep their darker world warm enough to prevent water at Earth’s surface from freezing. Future research could clarify the issue, Wolf notes. [Science News]

This all means that Earth's baby picture probably looked a lot like a current shot of Saturn's moon Titan.
Image
  • A thick organic haze similar to Titan's may have shrouded Earth several billion years ago, protecting primordial life on the planet from damaging ultraviolet radiation. (NASA/JPL/SSI)
  • Fractal Haze Could Solve Weak-Sun Mystery for Early Earth
    Wired Science - 03 June 2010
    A thick haze of organic material let the early Earth soak up the sun’s warmth without absorbing harmful ultraviolet rays, according to a new study.

    The model offers a new twist on an old puzzle: Although the sun was so dim billions of years ago that the Earth should have been a ball of ice, the young planet had liquid oceans capable of supporting life.
    ...
    The sun should have been up to 30 percent less bright 3.8 billion to 2.5 billion years ago, according to studies of the lifecycles of sun-like stars. If the Earth’s atmosphere had the same composition then as it does now, it would have frozen over completely, like Jupiter’s moon Europa. But geological records show the Earth was at least as warm and wet then as it is today.
    How Early Earth Got Warm and Hospitable
    Space.com - 03 June 2010
    Our planet might have kept warm in the super-ancient past when the sun was substantially dimmer than it is today because of a complex brew of global warming gases much like that now enveloping Saturn's moon Titan, scientists reveal.

    These new findings could also shed light on how the building blocks of life might have formed on Earth.

    When the sun was young, models suggest it was just 70 percent as bright as it is now. However, during the first two billion years or so of Earth's history, the surface of the planet was warm enough for glaciers to not form and early life to emerge.
    Hazy antidote to a faint young sun
    Science News - 03 June 2010
    New theory suggests atmospheric answer to the paradox about early Earth’s temperature

    How do you keep a chilly youngster warm? Wrap it in a blanket, of course. Turns out that a blanket of haze might have warmed Earth during its infancy, when the sun was substantially dimmer. That might have kept the planet from freezing, as some studies suggest its fate would have been otherwise.

    Theories abound about why Earth didn’t freeze during the first half of its history, even though the sun was about 30 percent dimmer then than it is today. Just over a month ago, one team suggested that the planet kept warm billions of years ago by absorbing a larger fraction of the sun’s radiation (SN: 4/24/10, p. 11). In that early era, the researchers argued, light-colored continents were much smaller and light-scattering clouds covered less of Earth’s surface, so that, on the whole, Earth was darker.

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Re: CU: Early Earth Haze Likely Provided Ultraviolet Shield

Post by bystander » Sat Jun 05, 2010 7:40 am

Alien Climates Play Key Role in Possibility of Life
Astrobiology - 03 June 2010
A new study of how climate conditions have affected the origin and evolution of life on Earth could provide clues to understanding how climates on alien planets might affect their potential for life.

Greenhouse gases have a bad reputation because of the role they’re playing in global warming on Earth today. However, scientists say we also owe our lives to greenhouse gases because they might have allowed life to take hold in the first place.

A new study of how these and other climate conditions have affected the origin and evolution of life on Earth could provide clues to understanding how climates on alien planets might affect their potential life.

Greenhouse gases heat the planet by letting light in and then trapping heat beneath, increasing the ambient temperature of the ground.

Scientists think the Sun used to shine less brightly when the Earth was young, so the early Earth should have been cooler than it is today. But greenhouse gases such as methane and carbon dioxide played an important role at this time, warming the planet to a point where it was habitable for life.

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TR: Faint Young Sun Paradox Not Solved

Post by bystander » Thu Jun 02, 2011 3:53 am

Faint Young Sun Paradox Not Solved, Says NASA
Technology Review | The Physics arXiv Blog | kfc | 2011 May 31
Last year, scientists claimed to have solved the faint young Sun paradox. They were wrong. Now the paradox is back and more puzzling than ever.

Liquid water has flowed on Earth for some 3.8 billion years, since not long after the planet formed. The evidence comes from rocks that date from that period which seem to have formed under the action of water.

But this presents palaeontologists and geologists with a problem. At that time, the Sun was some 30 per cent dimmer than it is today and would not have provided enough heat to keep water liquid on the surface.

This is known as the faint young Sun paradox and it has puzzled scientists since the 1970s when astronomers first pointed it out. But it didn't really worry anybody. The obvious solutions are that the Earth was warmer because it reflected less heat from the Sun, it had a lower albedo, or that it was victim of a runaway greenhouse effect. One of these must be right but nobody was sure which.

But last year, a group of researchers claimed to have solved the paradox. They said that the make up of rocks from that time exclude the possibility that the atmosphere was rich in a greenhouse gas such as methane or carbon dioxide.

Instead, the Earth must have had a lower albedo and therefore must have absorbed more heat from the Sun than it does today. The lower albedo, they argued, was the result of fewer biological particles in the atmosphere. These nucleate water droplet formation. So without them there would be fewer clouds and less sunlight reflected into space.

These guys published their solution in Nature[1] and the problem was thought to have been solved. (We looked at another mechanism that may have prevented cloud formation in the early atmosphere about a year ago.)

But today Colin Goldlatt and Kevin Zahnle[4] at NASA's Ames Research Center in Moffett Field re-ignite the controversy.

They've looked at this problem again and studied the effect of fewer clouds. They say that however you do the numbers, this could not have made the Earth hot enough to allow the existence of liquid water.

Clouds have two effects. In general, high clouds trap heat while low clouds reflect it. "Therefore the absolute upper bound on warming by decreasing cloud reflectivity would be found by removing low clouds entirely," they say.

When you do that in a computer model of the Earth's early climate, you get no more than half the heating necessary to maintain liquid water on the surface.

"We show that, even with the strongest plausible assumptions, reducing cloud and surface albedos falls short by a factor of two of resolving the paradox," say Goldlatt and Zahnle.

So the paradox is alive and well; and more puzzling than ever. Last year we discovered that a greenhouse effect can't explain the paradox. Now we know that a lower albedo wouldn't have done the trick either.

So the race is back on to nail this problem once and for all. Get your thinking caps on.
  1. No climate paradox under the faint early Sun - MT Rosing, DK Bird, NH Sleep, CJ Bjerrum
  2. Mineralogical constraints on Precambrian pCO2 - CT Reinhard, NJ Planavsky
  3. Low pCO2 in the pore water, not in the Archean air - N Dauphas, J F Kasting
  4. Faint young Sun paradox remains - C Goldblatt, KJ Zahnle
  5. Rosing, Bird, Sleep & Bjerrum reply - MT Rosing, DK Bird, NH Sleep, CJ Bjerrum
A Solution to the Faint Young Sun Paradox
Technology Review | The Physics arXiv Blog | kfc | 2010 Apr 02
The strange behavior of a nearby, young, sun-like star could help solve one of the outstanding mysteries in astronomy.
Image
When it comes to the origin of life on Earth some four billion years ago, there's a problem. At that time, the young Sun was approximately 75 percent dimmer than it is now. That would have made the Earth significantly colder, in fact, too cold for liquid water.

However, we know that liquid water is essential for life and we know from the fossil record that life existed on Earth at the time. Liquid water must have been present. So what was keeping the water warm?

This problem, known as the faint young Sun paradox, has troubled astronomers since the 1970s, when it was pointed out by Carl Sagan and friends. He proposed that the Earth's atmosphere at that time must have been rich in carbon dioxide and that the consequent greenhouse effect was responsible for the warming. Other evidence, however, suggests that the atmosphere could not have had enough CO2 to do the trick. The arXiv Blog has looked at other possible solutions in the past too.

Today, Christoffer Karoff at the University of Birmingham and a mate make a new suggestion based on their study of kappa Ceti, a star some 30 light years away in the constellation of Cetus which is very much like our Sun as it would have been four billion years ago.

It turns out that Kappa Ceti is little more interesting than astronomers once thought. This young star, says Karoff, produces flares and coronal mass ejections at a rate that is three orders of magnitude greater than our Sun today. The implication, of course, is that our Sun must have been just as active when it was the same age as kappa Ceti (about 700 million years old).

But so what? How can coronal mass ejections have made the Earth hotter? The answer lies in a phenomenon known as the Forbush decrease, after the astronomer Scott Forbush who studied galactic comsic rays in the 1930s and 1940s.

Forbush discovered that the number of galactic cosmic rays hitting Earth drops by up to 30 per cent within a day or so of the Sun producing a coronal mass ejection. The reason is that these ejections are giant clouds of ionised gas enveloped in powerful magnetic fields. These fields simply steer the cosmic rays away from Earth.

So if the early Sun was producing far more coronal mass ejections, far fewer cosmic rays would have arrived on Earth.

And that's where another idea comes into play. In recent years, various climatologists have speculated that cosmic rays seed the formation of clouds in the lower atmosphere. The idea is that they ionise molecules and dust particles which then become focal points for droplets to condense on.

So fewer cosmic rays lead to fewer clouds. There is even some evidence that cloud cover drops during a Forbush decrease, although it's fair to say there is some dispute over this.

So Karoff's thinking goes like this. More coronal mass ejections in Earth's past lead to fewer cosmic rays hitting Earth which lead to less cloud cover. Less cloud cover meant that less sunlight would have been reflected back into space which would have allowed the surface to heat up.

And that's what kept water liquid on the Earth's surface four billion years ago.

Got that?
How did the Sun affect the climate when life evolved on the Earth? - C. Karoff, H. Svensmark Solving the faint young Sun problem
the physics arXiv blog | kfc | 2008 Apr 29
We know by studying ancient rocks that liquid water existed on the surface of Earth at least 3.7 billion years ago. That implies that the surface temperature at that time was at least 273K.

We also know by studying stars similar to ours that the Sun must have been significantly less bright than it is now (Sol is thought to have increased in luminosity by 30 per cent since then). That ought to have resulted in temperatures on Earth that were well below freezing.

This contradiction is known as the “faint young Sun” problem and nobody has adequately explained it.

The most common explanation is that the planet must have been warmed by some kind of greenhouse gas effect mediated perhaps by carbon dioxide, atmospheric haze, ammonia or methane. The trouble is that the evidence indicates that these gases existred in quantities at least an order of magnitude too little to have done the job.

So what gives? According to Philip von Paris of the Institute of Planetary Research at the German Aerospace Centre in Berlin, Germany, und Freunds, the mix up is largely the result of an error in our understanding of how much radiation was absorbed in those days. His team has used a new atmospheric model of the early Earth to determine that the required green house effect would have been possible with carbon dioxide with a partial pressure of about 2.9mb, about an order of magnitude less than previously thought.

That’s a pretty good match with the amount of carbon dioxide thought to have been around between 2 and 2.5 billion years ago. Nice result. But von Paris has been a little over ambitious. He says: “thus, the contradiction between sediment data and model results disappears,” implying that the faint young Sun problem is solved.

But hang on a minute, he seems to have forgotten the billion years or so between 2.5 and 3.7 billion years ago in which the temperature is still unexplained.

Nice try, von Paris. But we’re not that easily foooled.
Warming the early Earth - CO2 reconsidered - P von Paris et al
  • arXiv.org > astro-ph > arXiv:0804.4134 > 25 Apr 2008 (v1), 11 Sep 2008 (v2)
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Re: CU: Early Earth Haze Likely Provided Ultraviolet Shield

Post by neufer » Thu Jun 02, 2011 10:29 am

http://en.wikipedia.org/wiki/Bart%27s_Comet wrote:
<<After Bart sabotages Principal Skinner's weather balloon, Skinner decides to punish him by having him help with his amateur astronomy. Skinner dreams of finding something in the sky and having it named after him. Bart accidentally locates a comet which is named after him. Scientists soon discover that the comet is heading straight for Springfield. Professor Frink plans to launch a missile at the comet, dispelling everyone's fears (save only by Lisa, who knows that this plan can backfire, and Moe, because in any circumstance, his tavern will be destroyed anyway). However, the missile flies past the comet, instead blowing up the only bridge out of town. After a Congressional bill to evacuate Springfield is defeated, Homer decides that they should stay in the bomb shelter that Ned Flanders built. Anticipating this, Ned had built it large enough for both families. One hour before Springfield is destroyed, the rest of the townspeople arrive, demanding a place in the bunker. Homer is unable to close the door and someone has to leave. Homer decides that the only thing the "world of the future" will not need is left-handed stores and tells Ned to go. Eventually, Homer feels guilty and leaves as well, followed by the other townspeople and they all converge on a hill to await death.
Image
Comet breaks up in Springfield's extra-thick layer of pollution
  • The comet enters the atmosphere, breaking up.

    MARGE: Look!

    LISA: It's breaking up!

    The comet breaks up more, until it becomes just a small rock. The rock makes a hole in Skinner's weather balloon, deflating it, then rebounds off Ned's bomb shelter, knocking it to the ground.

    BART: [picking up comet] Cool!

    LISA: We're saved!

    Everyone cheers.

    SELMA: Sure makes you appreciate the preciousness of life. (lights a cigarette)

    MOE: Let's go burn down the observatory so this'll never happen again.

    Everyone leaves, except for the Simpson family.

    LISA: I can't believe that extra-thick layer of pollution that I've picketed against is what burned up the comet.

    BART: But what's really amazing, is that this is exactly what Dad said would happen.

    LISA: Yeah, Dad was right...

    HOMER: I know, kids. I'm scared too!>>
Art Neuendorffer