Study Details Why Super-Earths Have Long-Lasting Oceans

This artist’s depiction shows a gas giant planet rising over the horizon of an alien waterworld.

A newly published study from the Harvard-Smithsonian Center for Astrophysics reveals why oceans on super-Earths, once established, can last for billions of years.
Cambridge, Massachusetts – For life as we know it to develop on other planets, those planets would need liquid water, or oceans. Geologic evidence suggests that Earth’s oceans have existed for nearly the entire history of our world. But would that be true of other planets, particularly super-Earths? New research suggests the answer is yes and that oceans on super-Earths, once established, can last for billions of years.
“When people consider whether a planet is in the habitable zone, they think about its distance from the star and its temperature. However, they should also think about oceans, and look at super-Earths to find a good sailing or surfing destination,” says lead author Laura Schaefer of the Harvard-Smithsonian Center for Astrophysics (CfA).
Schaefer presented her findings today in a press conference at a meeting of the American Astronomical Society.
Even though water covers 70 percent of Earth’s surface, it makes up a very small fraction of the planet’s overall bulk. Earth is mostly rock and iron; only about a tenth of a percent is water.
“Earth’s oceans are a very thin film, like fog on a bathroom mirror,” explains study co-author Dimitar Sasselov (CfA).
However, Earth’s water isn’t just on the surface. Studies have shown that Earth’s mantle holds several oceans’ worth of water that was dragged underground by plate tectonics and subduction of the ocean seafloor. Earth’s oceans would disappear due to this process, if it weren’t for water returning to the surface via volcanism (mainly at mid-ocean ridges). Earth maintains its oceans through this planet-wide recycling.
Schaefer used computer simulations to see if this recycling process would take place on super-Earths, which are planets up to five times the mass, or 1.5 times the size, of Earth. She also examined the question of how long it would take oceans to form after the planet cooled enough for its crust to solidify.
She found that planets two to four times the mass of Earth are even better at establishing and maintaining oceans than our Earth. The oceans of super-Earths would persist for at least 10 billion years (unless boiled away by an evolving red giant star).
Interestingly, the largest planet that was studied, five times the mass of Earth, took a while to get going. Its oceans didn’t develop for about a billion years, due to a thicker crust and lithosphere that delayed the start of volcanic outgassing.
“This suggests that if you want to look for life, you should look at older super-Earths,” Schaefer says.
Sasselov agrees. “It takes time to develop the chemical processes for life on a global scale, and time for life to change a planet’s atmosphere. So, it takes time for life to become detectable.”
This also suggests that, assuming evolution takes place at a similar rate to Earth’s, you want to search for complex life on planets that are about five and a half billion years old, a billion years older than Earth.
Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.
Publication: Accepted for publication at the Astrophysical Journal
PDF Copy of the Study: The persistence of oceans on Earth-like planets: insights from the deep-water cycle
Source: Harvard-Smithsonian Center for Astrophysics

Lack of oxygen delayed the rise of animals on Earth | scitamil.blogspot.com

Christopher Reinhard and Noah Planavsky conduct research for the study in China. | sci-english.blogspot.com

Geologists are letting the air out of a nagging mystery about the development of animal life on Earth.

Scientists have long speculated as to why animal species didn't flourish sooner, once sufficient oxygen covered Earth's surface. Animals began to prosper at the end of the Proterozoic period, about 800 million years ago -- but what about the billion-year stretch before that, when most researchers think there also was plenty of oxygen?
Well, it seems the air wasn't so great then, after all.
In a study published Oct. 30 in Science, Yale researcher Noah Planavsky and his colleagues found that oxygen levels during the "boring billion" period were only 0.1% of what they are today. In other words, Earth's atmosphere couldn't have supported a diversity of creatures, no matter what genetic advancements were poised to occur.
"There is no question that genetic and ecological innovation must ultimately be behind the rise of animals, but it is equally unavoidable that animals need a certain level of oxygen," said Planavsky, co-lead author of the research along with Christopher Reinhard of the Georgia Institute of Technology. "We're providing the first evidence that oxygen levels were low enough during this period to potentially prevent the rise of animals."
The scientists found their evidence by analyzing chromium (Cr) isotopes in ancient sediments from China, Australia, Canada, and the United States. Chromium is found in Earth's continental crust, and chromium oxidation is directly linked to the presence of free oxygen in the atmosphere.
Specifically, the team studied samples deposited in shallow, iron-rich ocean areas, near the shore. They compared their data with other samples taken from younger locales known to have higher levels of oxygen.
Oxygen's role in controlling the first appearance of animals has long vexed scientists. "We were missing the right approach until now," Planavsky said. "Chromium gave us the proxy." Previous estimates put the oxygen level at 40% of today's conditions during pre-animal times, leaving open the possibility that oxygen was already plentiful enough to support animal life.
In the new study, the researchers acknowledged that oxygen levels were "highly dynamic" in the early atmosphere, with the potential for occasional spikes. However, they said, "It seems clear that there is a first-order difference in the nature of Earth surface Cr cycling" before and after the rise of animals.
"If we are right, our results will really change how people view the origins of animals and other complex life, and their relationships to the co-evolving environment," said co-author Tim Lyons of the University of California-Riverside. "This could be a game changer."
"There's a lot of interest right now in a broader discussion surrounding the role that environmental stability played in the evolution of complex life, and we think our results are a significant contribution to that," Reinhard said.
Funding sources for the research included the NASA Exobiology Program and the National Science Foundation's Earth-Life Transitions program, awarded to Planavsky, Reinhard, and Lyons.
The other members of the research team included Xiangli Wang, a postdoctoral fellow at Yale; Thomas Johnson, of the University of Illinois; Danielle Thomson, of Carleton University; Peter McGoldrick, of the University of Tasmania; and Woodward Fischer, of the California Institute of Technology.

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Story Source:
The above story is based on materials provided by Yale University. The original article was written by Jim Shelton. Note: Materials may be edited for content and length.

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Journal Reference:

1. N. J. Planavsky, C. T. Reinhard, X. Wang, D. Thomson, P. McGoldrick, R. H. Rainbird, T. Johnson, W. W. Fischer, T. W. Lyons. Low Mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals. Science, 2014; 346 (6209): 635 DOI: 10.1126/science.1258410

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3-D map of the adolescent universe | sci-english.blogspot.com

3D map of the cosmic web at a distance of 10.8 billion years from Earth | sci-english.blogspot.com

 

Using extremely faint light from galaxies 10.8-billion light years away, scientists have created one of the most complete, three-dimensional maps of a slice of the adolescent universe. The map shows a web of hydrogen gas that varies from low to high density at a time when the universe was made of a fraction of the dark matter we see today.

The new study, led by Khee-Gan Lee and his team at the Max Planck Institute for
Astronomy in conjunction with researchers at Berkeley Lab and UC Berkeley, will be
published in an upcoming issue of Astrophysical Journal Letters.
In addition to providing a new map of part of the universe at a young age, says David Schlegel of Berkeley Lab, the work demonstrates a novel technique for high-resolution universe maps. The new technique, which uses distant galaxies to backlight hydrogen gas, might inform future mapping projects, he says. One such project could be the proposed Dark Energy Spectroscopic Instrument (DESI). Managed by Berkeley Lab, DESI has the goal of producing the most complete map of the universe yet.
"DESI was designed without the possibility of extracting such information from the most distant, faint galaxies," says Schlegel, "Now that we know this is possible, DESI promises to be even more powerful."
The first big 3D map of the universe was created using data from the Sloan Digital Sky Survey (SDSS), which began in 1998. Over the years, the survey has provided data to make a high-resolution map of the nearby universe, within about 1-billion light years. Recent telescope upgrades have stretched our ability to map the universe to about 6-billion light years, but, according to Schlegel, it's a fairly crude map with incomplete data in some areas. The next generation of maps will come from the DESI project, scheduled to begin operation in 2018 pending funding. DESI will allow scientists to visualize 10 times the volume of SDSS and will extend about 10-billion light years away.
Artist's impression illustrating the technique of Lyman-alpha tomography: as light from distant background galaxies (yellow arrows) travel through the Universe towards Earth, they are imprinted by the absorption signatures from hydrogen gas tracing in the foreground cosmic web. By observing a number of background galaxies in a small patch of the sky, astronomers were able to create a 3D map of the cosmic web using a technique similar to medical computer tomography (CT) scans. Credit: Khee-Gan Lee (MPIA) and Casey Stark (UC Berkeley)
Beyond 10-billion light years, says Schlegel, the expectation was that the map would become sparse. The reason: astronomers planned to use a familiar technique that uses the bright light of quasars, which are, unfortunately, scattered and few. The technique uses a phenomenon called Lyman-alpha forest absorption, which relies on the fact that vast clouds of hydrogen exist between Earth and distant quasars and galaxies. At a certain distance, as measured by the red shift of the light, astronomers can determine the density of hydrogen, based on the absorption of quasar light. The problem is that this only provides information about the presence of hydrogen along the line of sight, not over a larger volume of space.
"It's a pretty weird map because it's not really 3D," explains Schlegel. "It's all these skewers; we don't have a picture of what's between the quasars, just what's along the skewers."
The researchers believe their new technique, which uses the faint light of numerous distant galaxies instead of that of sparse quasars, can fill in the gaps between these skewers.
Before this study, no one knew if galaxies further than 10-billion light years away could provide enough light to be useful, Schlegel says. But earlier this year, the team collected four hours of data on the Keck-1 telescope during a brief break in cloudy skies. "It turned out to be enough time to prove we could do this," Schlegel says.
Of course, the galaxies' light was indeed exceedingly faint. In order to use it for a map, the researchers needed to develop algorithms to subtract light from the sky that would otherwise drown out the galactic signals. Schlegel developed the algorithm to do this, while Casey Stark and Martin White of UC Berkeley modified an existing algorithm, called a Wiener filter, to create the 3D map within a minute on a standard laptop computer.
Because the project was a proof-of-concept, the researchers are planning future Keck-1 telescope time to extend the volume of space they map. "This technique is pretty efficient and it wouldn't take a long time to obtain enough data to cover volumes hundreds of millions of light years on a side," says Khee-Gan Lee.
This research was supported by the U.S. Department of Energy's Office of Science and used the facilities of the National Energy Research Scientific Computing Center (NERSC) located at Berkeley Lab.
- See more at: http://newscenter.lbl.gov/2014/10/16/a-3d-map-of-the-adolescent-universe/#sthash.nCKqf8Tn.dpuf

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Story Source:
The above story is based on materials provided by Berkeley Laboratory. The original article was written by Kate Greene. Note: Materials may be edited for content and length.

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