Scientists predict greater longevity for planets with life
June 13, 2009
Roughly a billion years from now, the ever-increasing radiation from the sun will have heated Earth into inhabitability; the carbon dioxide in the atmosphere that serves as food for plant life will disappear, pulled out by the weathering of rocks; the oceans will evaporate; and all living things will disappear.
Or maybe not quite so soon, say researchers from the California Institute of Technology (Caltech), who have come up with a mechanism that doubles the future lifespan of the biosphere—while also increasing the chance that advanced life will be found elsewhere in the universe.
A paper describing their hypothesis was published June 1 in the early online edition of the Proceedings of the National Academy of Sciences (PNAS).
Earth maintains its surface temperatures through the greenhouse effect. Although the planet's greenhouse gases—chiefly water vapor, carbon dioxide, and methane—have become the villain in global warming scenarios, they're crucial for a habitable world, because they act as an insulating blanket in the atmosphere that absorbs and radiates thermal radiation, keeping the surface comfortably warm.
As the sun has matured over the past 4.5 billion years, it has become both brighter and hotter, increasing the amount of solar radiation received by Earth, along with surface temperatures. Earth has coped by reducing the amount of carbon dioxide in the atmosphere, thus reducing the warming effect. (Despite current concerns about rising carbon dioxide levels triggering detrimental climate change, the pressure of carbon dioxide in the atmosphere has dropped some 2,000-fold over the past 3.5 billion years; modern, man-made increases in atmospheric carbon dioxide offset a fraction of this overall decrease.)
The problem, says Joseph L. Kirschvink, the Nico and Marilyn Van Wingen Professor of Geobiology at Caltech and a coauthor of the PNAS paper, is that "we're nearing the point where there's not enough carbon dioxide left to regulate temperatures following the same procedures."
Kirschvink and his collaborators Yuk L. Yung, a Caltech professor of planetary science, and graduate students King-Fai Li and Kaveh Pahlevan, say that the solution is to reduce substantially the total pressure of the atmosphere itself, by removing massive amounts of molecular nitrogen, the largely nonreactive gas that makes up about 78 percent of the atmosphere. This would regulate the surface temperatures and allow carbon dioxide to remain in the atmosphere, to support life, and could tack an additional 1.3 billion years onto Earth's expected lifespan.
In the "blanket" analogy for greenhouse gases, carbon dioxide would be represented by the cotton fibers making up the blanket. "The cotton weave may have holes, which allow heat to leak out," explains Li, the lead author of the paper.
"The size of the holes is controlled by pressure," Yung says. "Squeeze the blanket," by increasing the atmospheric pressure, "and the holes become smaller, so less heat can escape. With less pressure, the holes become larger, and more heat can escape," he says, helping the planet to shed the extra heat generated by a more luminous sun.
Strikingly, no external influence would be necessary to take nitrogen out of the air, the scientists say. Instead, the biosphere itself would accomplish this, because nitrogen is incorporated into the cells of organisms as they grow, and is buried with them when they die.
In fact, "This reduction of nitrogen is something that may already be happening," says Pahlevan, and that has occurred over the course of Earth's history. This suggests that Earth's atmospheric pressure may be lower now than it was earlier in the planet's history.
Proof of this hypothesis may come from other research groups that are examining the gas bubbles formed in ancient lavas to determine past atmospheric pressure: the maximum size of a forming bubble is constrained by the amount of atmospheric pressure, with higher pressures producing smaller bubbles, and vice versa.
If true, the mechanism also would potentially occur on any extrasolar planet with an atmosphere and a biosphere.
"Hopefully, in the future we will not only detect Earth-like planets around other stars but learn something about their atmospheres and the ambient pressures," Pahlevan says. "And if it turns out that older planets tend to have thinner atmospheres, it would be an indication that this process has some universality."
Adds Yung: "We can't wait for the experiment to occur on Earth. It would take too long. But if we study exoplanets, maybe we will see it. Maybe the experiment has already been done."
Increasing the lifespan of our biosphere—from roughly 1 billion to 2.3 billion years—has intriguing implications for the search for life elsewhere in the universe. The length of the existence of advanced life is a variable in the Drake equation, astronomer Frank Drake's famous formula for estimating the number of intelligent extraterrestrial civilizations in the galaxy. Doubling the duration of Earth's biosphere effectively doubles the odds that intelligent life will be found elsewhere in the galaxy.
"It didn't take very long to produce life on the planet, but it takes a very long time to develop advanced life," says Yung. On Earth, this process took four billion years. "Adding an additional billion years gives us more time to develop, and more time to encounter advanced civilizations, whose own existence might be prolonged by this mechanism. It gives us a chance to meet."
Source: California Institute of Technology (news : web)
Dec 20, 2007 |
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In the middle of the heated debate over global warming, it is intriguing that The Proceedings of the National Academy of Sciences (PNAS) would publish a paper described by statements like these:
"Although the planet's greenhouse gases . . . have become the villain in global warming scenarios, they're crucial for a habitable world."
"As the sun has matured over the past 4.5 billion years, it has become both brighter and hotter, . . . "
. . . "we're nearing the point where there's not enough carbon dioxide left to regulate temperatures . . ."
There is more to this paper than meets the eye.
This may be a signal that the National Academy of Sciences (NAS) is backing away from past statements of certainty that
a.) Earth's climate is immune to changes in the Sun, and
b.) Carbon dioxide is the villain that caused global warming?
With kind regards,
Oliver K. Manuel
http://myprofile....anuelo09
1) I don't think anyone said that the climate is immune to changes in the sun. The current view is that the changes in the sun are not the dominating factor TODAY. This article talks about BILLIONS of years.
2) The NAS isn't backing away from anything. That is your imagination.
3) CO2 is the probable cause for the warming that we are seeing now. Taking all other factors into account the Earth is warming and rising CO2 is the critical factor according to both theoretical (models) and experimental evidence. Looking at the CO2 sources and sinks CO2 due to burning by man is the contribution that tracks the evidence.
If you don't believe this I wish you well because it doesn't really matter to me what your belief is as long as the consensus leads to a solution.
No, nitrogen is not very reactive on its own, which is why minerals in general lack the substance.
However, various forms of life can process nitrogen into other compounds and these compounds can be sequestered and buried. So long as the nitrogen is not released by other processes, this method would probably work over a long period of time.
Unfortunately, we lack the technology to do this relatively soon on such a large scale as would be necessary to remove such large amounts of nitrogen at present.
I think it would be better just to increase CO2 level to a level which would do the same thing. We would get a better buffer for the future in the interim.
Besides,scientist's are studying a planet bigger then the size of the sun, that they say is going to crush the Earth by 2012.The planet is going to change the orbiting state of the earth, distroy most the biosphere, and change the position of the sunrise to the west(this study is still not proved). So, in my point of view, i think it is better for scientist's to start of with priorities, and not something that's going to out run the biosphere a billion years from now.
And Timefighter, I suspect that the "scientists" who think that are only considered to be scientists by themselves. (A.) It's not really possible for a planet to be larger than a star without becoming a star, (B.) if a star were going to hit our world in three years it would be the brightest star in the night sky, and would probably also be visible during the day, and (C.) if such a collision were imminent, there would not be the slightest thing we could do to survive or to save our world.
That's why historical evidence shows warming preceding CO2 increases? Or why the last 8 years have been cooling even with CO2 increases?
What consensus? The 30 to 50 biased scientists that wrote the IPCC report? The thousands that believed that the Earth is the center of the universe? Those that believed the world is flat? Those that believed in phlostigen?
Actually, you are pretty close to correct. When photosynthetic life held sway the CO2 levels in earth's atmosphere were not a whole lot above 7000 ppm.
The problem with the Nitrogen Cycle is that is just that. It is part of the cycle in plants but becomes part of the rest of the food chain. It is recycled rather than buried in the rocks. It is there but not in the amounts we see of CO2.
Most of the nitrogen ends up in soil rather than in rock. However, given that the atmosphere is ~78% nitrogen it is highly unlikely that it ever would be used up by natural means. The scientists who wrote the paper actually want to modify how life deals with nitrogen and bury it directly rather than let life take its course.
In my opinion, adding the CO2 to the atmosphere is the better and much easier solution.