Study shows how early Earth kept warm enough to support life

Jul 09, 2013
This is an artist's conception of the Earth during the late Archean, 2.8 billion years ago. Weak solar radiation requires the Earth have increased greenhouse gas amounts to remain warm. CU-Boulder doctoral student Eric Wolf Wolf and CU-Boulder Professor Brian Toon use a three-dimensional climate model to show that the late Archean may have maintained large areas of liquid surface water despite a relatively weak greenhouse. With carbon dioxide levels within constraints deduced from ancient soils, the late Archean may have had large polar ice caps but lower latitudes would have remained temperate and thus hospitable to life. The addition of methane allows the late Archean to warmed to present day mean surface temperatures. Credit: Charlie Meeks

Solving the "faint young sun paradox"—explaining how early Earth was warm and habitable for life beginning more than 3 billion years ago even though the sun was 20 percent dimmer than today—may not be as difficult as believed, says a new University of Colorado Boulder study.

In fact, two CU-Boulder researchers say all that may have been required to sustain liquid water and primitive life on Earth during the Archean eon 2.8 billion years ago were reasonable amounts believed to be present at the time and perhaps a dash of methane. The key to the solution was the use of sophisticated three-dimensional that were run for thousands of hours on CU's Janus supercomputer, rather than crude, one-dimensional models used by almost all scientists attempting to solve the paradox, said doctoral student Eric Wolf, lead study author.

"It's really not that hard in a three-dimensional climate model to get average surface temperatures during the Archean that are in fact moderate," said Wolf, a doctoral student in CU-Boulder's atmospheric and oceanic sciences department. "Our models indicate the Archean climate may have been similar to our present climate, perhaps a little cooler. Even if Earth was sliding in and out of back then, there still would have been a large amount of liquid water in equatorial regions, just like today."

Evolutionary biologists believe life arose on Earth as simple cells roughly 3.5 billion years ago, about a billion years after the planet is thought to have formed. Scientists have speculated the first life may have evolved in shallow tide pools, freshwater ponds, freshwater or deep-sea hydrothermal vents, or even arrived on objects from space.

A cover article by Wolf and Professor Brian Toon on the topic appears in the July issue of Astrobiology. The study was funded by two NASA grants and by the National Science Foundation, which supports CU-Boulder's Janus supercomputer used for the study.

Scientists have been trying to solve the faint young sun paradox since 1972, when Cornell University scientist Carl Sagan—Toon's doctoral adviser at the time—and colleague George Mullen broached the subject. Since then there have been many studies using 1-D climate models to try to solve the faint young sun paradox—with results ranging from a hot, tropical Earth to a "snowball Earth" with runaway glaciation—none of which have conclusively resolved the problem.

"In our opinion, the one-dimensional models of early Earth created by scientists to solve this paradox are too simple—they are essentially taking the early Earth and reducing it to a single column atmospheric profile," said Toon. "One-dimensional models are simply too crude to give an accurate picture."

Wolf and Toon used a general circulation model known as the Community Atmospheric Model version 3.0 developed by the National Center for Atmospheric Research in Boulder and which contains 3-D atmosphere, ocean, land, cloud and sea ice components. The two researchers also "tuned up" the model with a sophisticated radiative transfer component that allowed for the absorption, emission and scattering of solar energy and an accurate calculation of the greenhouse effect for the unusual atmosphere of early Earth, where there was no oxygen and no ozone, but lots of CO2 and possibly methane.

The simplest solution to the faint sun paradox, which duplicates Earth's present climate, involves maintaining roughly 20,000 parts per million of the greenhouse gas CO2 and 1,000 ppm of methane in the ancient atmosphere some 2.8 billion years ago, said Wolf. While that may seem like a lot compared to today's 400 ppm of CO2 in the atmosphere, geological studies of ancient soil samples support the idea that CO2 likely could have been that high during that time period. Methane is considered to be at least 20 times more powerful as a greenhouse gas than CO2 and could have played a significant role in warming the early Earth as well, said the CU researchers.

There are other reasons to believe that CO2 was much higher in the Archean, said Toon, who along with Wolf is associated with CU's Laboratory for Atmospheric and Space Physics. The continental area of Earth was smaller back then so there was less weathering of the land and a lower release of minerals to the oceans. As a result there was a smaller conversion of CO2 to limestone in the ocean. Likewise, there were no "rooted" land plants in the Archean, which could have accelerated the weathering of the soils and indirectly lowered the atmospheric abundance of CO2, Toon said.

Another solution to achieving a habitable but slightly cooler climate under the faint sun conditions is for the Archean atmosphere to have contained roughly 15,000 to 20,000 ppm of CO2 and no methane, said Wolf. "Our results indicate that a weak version of the faint young sun paradox, requiring only that some portion of the planet's surface maintain liquid water, may be resolved with moderate greenhouse gas inventories," the authors wrote in Astrobiology.

"Even if half of Earth's surface was below freezing back in the Archean and half was above freezing, it still would have constituted a habitable planet since at least 50 percent of the ocean would have remained open," said Wolf. "Most scientists have not considered that there might have been a middle ground for the climate of the Archean.

"The leap from one-dimensional to three-dimensional models is an important step," said Wolf. "Clouds and sea ice are critical factors in determining climate, but the one-dimensional models completely ignore them."

Has the faint young sun paradox finally been solved? "I don't want to be presumptuous here," said Wolf. "But we show that the paradox is definitely not as challenging as was believed over the past 40 years. While we can't say definitively what the atmosphere looked like back then without more geological evidence, it is certainly not a stretch at all with our model to get a warm early Earth that would have been hospitable to life."

"The Janus supercomputer has been a tremendous addition to the campus, and this early Earth climate modeling project would have impossible without it," said Toon. The researchers estimated the project required roughly 6,000 hours of supercomputer computation time, an effort equal to about 10 years on a home computer.

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User comments : 12

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Howhot
4.1 / 5 (19) Jul 09, 2013
That is some great work by the researchers of CU-Boulder's atmospheric and oceanic sciences department. This is some excellent atmospheric computer modeling. It's fascinating to ponder what Earth must have been like 3 billion years ago, 20,000ppm CO2, 1000ppm methane, and a Sun that was 20% less bright as today. It really does demonstrate how good our atmospheric climate models have gotten. Great work.
cantdrive85
1.2 / 5 (20) Jul 10, 2013
GIGO! This is probably one of the smug JA's I get stuck behind left lane camping driving into Boulder.
VendicarE
3.8 / 5 (11) Jul 10, 2013
CantDriveTooStupid doesn't like science. He remembers in public school that it made his hands smell bad and when he set his notebook on fire he was frightened, and soiled his underpants.

These days, he wears depends. Just to be sure that science doesn't do it to him again.

Sanescience
1.4 / 5 (11) Jul 10, 2013
"The key to the solution was the use of sophisticated three-dimensional climate models that were run for thousands of hours on CU's Janus supercomputer, rather than crude, one-dimensional models used by almost all scientists attempting to solve the paradox"

Um, he didn't just imply that climate models until recently weren't working, did he?

I know, I know. Before the use of the lowest tiers of Graham's Hierarchy of Disagreement are spewed forth onto the screen by the cognitively fixated, I am not opposed to AGW being a possibility. And it is obvious that man is having substantial affect on Earths systems.

That said I state and have stated before that software models of chaotic systems should viewed with far more skepticism than they are frequently given. I've built simulation software and have done analysis of correctness using the very limited set of rigorous techniques for doing so. The result was always the same, humans are just really crappy at writing software.
cantdrive85
1.4 / 5 (18) Jul 10, 2013
CantDriveTooStupid doesn't like science. He remembers in public school that it made his hands smell bad and when he set his notebook on fire he was frightened, and soiled his underpants.

These days, he wears depends. Just to be sure that science doesn't do it to him again.


Science is great, even without eyebrows. However, this ain't science. It's Oscar fodder, it's value is equivalent to the paper it's printed on, about $0.13. As I said, GIGO. Unfortunately, it probably cost taxpayers thousands in wasted resources.
alfie_null
4.6 / 5 (13) Jul 10, 2013
Science is great, even without eyebrows. However, this ain't science. It's Oscar fodder, it's value is equivalent to the paper it's printed on, about $0.13. As I said, GIGO. Unfortunately, it probably cost taxpayers thousands in wasted resources.

You have specific aspects of this research you are dissatisfied with? Or maybe you'd prefer not to go into that. Trying to defend your view not appealing?

BTW, I paid my ISP something like $0.000001 to receive your nugget of wisdom (I didn't print it). Its value is somewhat less.
Egleton
2.8 / 5 (10) Jul 10, 2013
"I love science, but don't spend any money on it. We need it to bomb women and kids in faraway lands."
So tell me, How is the war going in Vietnam or Afganistan or even teeny tiny Eritrea? Mind you you did a fine number Grenada- I must give you that.
I don't know how you can face the shaving mirror.
Torbjorn_Larsson_OM
5 / 5 (7) Jul 10, 2013
I'm pleased, because that is what earlier revisions of atmospheric models implies, carbon dioxide on its own can solve the early Earth warming.

But of course, meanwhile paleonthology has moved on and on one hand Isua BIFs at 3.8 billion years ago seems deposited by life while on the other Lane & Martin has found a homology between methanogenes metabolism and alkaline hydrothermal vent chemistry.

So Kasting is correct anyway, early Earth was likely comfortable because of life.

As for the crackpots, of course mentioning or hinting at "GIGO" means the individual is both ignorant of science (among them an EU crackpot, 'nuff said) and antiscience (did I mention the crackpotism?).

@Sanescience: AGW isn't "a possibility", it is the only remaining possibility due to its dominating likelihood, and it is the accepted climate science. [ https://en.wikipe...matology , http://en.wikiped...e_change ]
VendicarE
5 / 5 (5) Jul 10, 2013
"As I said, GIGO." - CantDriveTooStupid

it is funny that you evaluate your child like comprehension of how the world works at anywhere the level that could distinguish between Garbage and Measurement.

Pathetic.
deatopmg
1 / 5 (8) Jul 11, 2013
The authors did not take into consideration that Earth's atmospheric pressure at the time was on the order of 100 bar so this work is totally meaningless!

Who paid for the ~6000 hrs of computer time? What a waste.
cantdrive85
1 / 5 (11) Jul 11, 2013
The authors did not take into consideration that Earth's atmospheric pressure at the time was on the order of 100 bar so this work is totally meaningless!

This along with countless other factors that are unknown or assumed, not to mention the complete failure of current models ability to predict reality in the present. What "measurements" do you have from this epoch? Every measurement is implied, there is no direct measurement. Therefore, not science, it's closer to metaphysics or philosophy, there is no empirical data.
Sanescience
2 / 5 (5) Jul 15, 2013
As for the crackpots, of course mentioning or hinting at "GIGO" means the individual is both ignorant of science (among them an EU crackpot, 'nuff said) and antiscience (did I mention the crackpotism?).
@Sanescience: AGW isn't "a possibility", it is the only remaining possibility due to its dominating likelihood, and it is the accepted climate science.

Mankind's history is dominated by the unquestioning fervent and political application of science. Which is ironic because true adherents to science do not accept as truth anything except the most rigorous applications under the most isolated and controlled environments.

This is interpreted by those not practiced in science as some kind of weakness or flaw and a leverage to be exploited by those with agendas.

Sadly most people need a very high degree of certainty before taking action. So convincing one's self that the answer desired is the correct answer often leads to attacking dissent. The path to hell is paved with good

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