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[LINK] Two links from The Dragon’s Gaze about dying Venus and Mars

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The Dragon’s Gaze recently-ish had two interesting links examining Venus and Mars, two worlds in our solar system’s youth which could have been rather more Earth-like than at present. The first link was to the paper “Exploring the Inner Edge of the Habitable Zone with Fully Coupled Oceans”.

Rotation in planetary atmospheres plays an important role in regulating atmospheric and oceanic heat flow, cloud formation and precipitation. Using the Goddard Institute for Space Studies (GISS) three dimension General Circulation Model (3D-GCM) we investigate how the effects of varying rotation rate and increasing the incident stellar flux on a planet set bounds on a planet’s habitable zone with its parent star. From ensemble climate simulations we identify which factors are the primary controllers of uncertainty in setting these bounds. This is shown in particular for fully coupled ocean (FCO) runs — some of the first that have been utilized in this context. Results with a Slab Ocean (SO) of 100m mixed layer depth are compared with a similar study by Yang et al. 2014, which demonstrates consistency across models. However, there are clear differences for rotations rates of 1-16x present Earth sidereal day lengths between the 100m SO and FCO models, which points to the necessity of using FCOs whenever possible. The latter was recently demonstrated quite clearly by Hu & Yang 2014 in their aquaworld study with a FCO when compared with similar mixed layer ocean studies and by Cullum et al. 2014.

We also show how these results have implications for Venus in the early history of our Solar System since even at this time Venus received more solar flux than Earth does today while it may still have had a slow retrograde rotation. The Venus runs utilize a 2.9Gya solar spectrum generated with the code of Claire et al. 2012, a modern Venus topography with an ocean filling the lowlands (giving an equivalent depth of 310 meters if spread across the entire surface), atmosphere of 1 bar N2, CO2=0.4mb, CH4=0.001mb and present day orbital parameters, radius, & gravity. We demonstrate that ancient Venus could have had quite moderate surface temperatures given these assumptions.

The second link was to “The early geodynamic evolution of Mars-type planets”.

It is not clear whether Mars once possessed active tectonics, yet the question is critical for understanding the thermal evolution of Mars, and the origin and longevity of its early dynamo. To address these issues, we have coupled mantle flow simulations, together with parameterized core evolution models, to simulate the early evolution of Mars-like planets, and constrain the influence of early mobile-lid tectonics on core evolution. We have explored a wide parameter suite, encapsulating a range of uncertainties in initial conditions, rheological parameters, and surface strength. We present successful models that experience early mobile-lid behaviour, with a later transition into a stagnant-lid mode, which reproduce core dynamo histories similar to the magnetic history of early Mars.

Written by Randy McDonald

February 10, 2016 at 7:30 pm

[LINK] “New Type of Seafloor Vent Discovered, Dominated by Talc”

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At Discover‘s The Extremo Files, Jeffrey Marlow draws from the Nature Communications paper “Talc-dominated seafloor deposits reveal a new class of hydrothermal system” to describe a new kind of life-supporting seafloor vent.

In December, however, a team of researchers from the National Oceanography Centre and the University of Southampton in Southampton, England, published a remarkable new finding: a new type of hydrothermal vent.*

At the Von Damm Vent Field (VDVF) in the Caribbean Sea, diverging plates move apart at a mere 15 milimeters per year – much slower than most mid-ocean ridges. This didn’t seem to bode well for rigorous venting activity: “It was originally thought that ultra-slow spreading ridges would not be able to support hydorthermal activity,” notes Matthew Hodgkinson, a PhD student at the University of Southampton who led the study. “As the spreading rates get slower, you generally have a lower magma supply and less heat to power hydrothermal vent fields.”

Which is why the 1997 discovery of hydrothermal venting at the ultra-slow spreading Southwest Indian Ridge came as a surprise. VDVF follows in this tradition, and is even more surprising given its slightly off-axis position. Electron-rich 200-degree (C) water was supporting a rich ecosystem comprised of many endemic species. “We’d expect there to be no magma whatsoever,” Hodgkinson explains, “so what’s powering this kind of activity? And what are the chemical consequences?”

During two different expeditions in 2010 and 2013 to the vents, the Southampton researchers tried to get answers, retrieving rock samples and developing high-resolution bathymetric maps of VDVF. When the remotely operated vehicle Isis returned to the ship after a day of sampling with a basket full of rocks, “the scientists would swarm around to get their samples,” Hodgkinson recalls, “bring them inside, take a photo, and do a quick description.” The more detailed analysis of mineralogy and rock precipitation history would be done back in the lab over the coming months and years.

Ultimately, the team found something remarkable: the dominant mineral was talc, a magnesium-rich silicate mineral perhaps best known for its softness and starring role in cosmetics products. It’s an unusual mineral to see at the seafloor, likely attributable the high pH values at VDVF (6) compared to those found at canonical black smokers (2-4). With a higher pH, the concentration of dissolved metals remains low, allowing silica to serve as a more prominent mineralogical player.

Written by Randy McDonald

February 10, 2016 at 5:08 pm

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[LINK] “Earth from afar would look only 82% right for life”

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Universe Today’s Evan Gough writes about an amusing analysis of Earth’s suitability for life.

You might think, because, well, here we are, that the Earth would look 100% habitable from a distant location. But that’s not the case. According to a paper from Rory Barnes and his colleagues at the University of Washington-based Virtual Planetary Laboratory, from a distant point in the galaxy, the probability of Earth being habitable might be only 82%.

Barnes and his team came up with the 82% number when they worked to create a “habitability index for transiting planets,” that seeks to rank the habitability of planets based on factors like the distance from its star, the size of the planet, the nature of the star, and the behaviour of other planets in the system.

The search for habitable exo-planets is dominated by the idea of the circumstellar habitable zone—or Goldilocks Zone—a region of space where an orbiting planet is not too close to its star to boil away all the water, and not so far away that the water is all frozen. This isn’t a fixed distance; it depends on the type and size of the star. With an enormous, hot star, the Goldilocks Zone would be much further away than Earth is from the Sun, and vice-versa for a smaller, cooler star. “That was a great first step, but it doesn’t make any distinctions within the habitable zone,” says Barnes.

To rank candidates for further study, Barnes focused on not just the distance between the planet and the host star, but on the overall energy equilibrium. That takes into account not just the energy received by the planet, but the planet’s albedo—how much energy it reflects back into space. In terms of being warm enough for life, a high-albedo planet can tolerate being closer to its star, whereas a low-albedo planet can tolerate a greater distance. This equilibrium is affected in turn by the eccentricity of the planet’s orbit.

The habitability index created by Barnes—and his colleagues Victoria Meadows and Nicole Evans—is a way to enter data, including a planet’s albedo and its distance from its host star, and get a number representing the planet’s probability of being habitable. “Basically, we’ve devised a way to take all the observational data that are available and develop a prioritization scheme,” said Barnes, “so that as we move into a time when there are hundreds of targets available, we might be able to say, ‘OK, that’s the one we want to start with.’”

So where does the Earth fit into all this? If alien astronomers are creating their own probability index, at 82%, Earth is a good candidate. Maybe they’re already studying us more closely.

The University of Washington press release is here, and the paper is at arXiv, “Comparative Habitability of Transiting Exoplanets”.

Written by Randy McDonald

February 8, 2016 at 8:37 pm

[LINK] “Tracing Slaves to Their African Homelands”

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National Geographic‘s Andrew Lawler reports on technological advances, including DNA, which are allowing researchers to discover the origins of slave populations throughout the Atlantic world.

“This will change our understanding of population and migration histories,” says Hannes Schroeder, a biological anthropologist at the University of Copenhagen. “What was just potential is now being fulfilled.”

One example comes from a 17th century cemetery on the Dutch side of the Caribbean island of St. Martin. When archaeologists excavated the site in 2010, they noticed filed teeth in the skulls of two men and a woman. The three individuals were between 25 and 40 years old when they died in the late 1600s.

Since teeth filing was a common practice in sub-Saharan Africa, it was a good bet that the individuals were enslaved Africans brought to the colony in the days of sugar plantations.

Just five years ago, that would have been the end of the story. An attempt to extract DNA from the skeletons to learn more about their identity would have been quixotic, since hot and humid weather degrades genetic material.

“These were badly preserved,” said Schroeder. “They had been laying under a Caribbean beach for four hundred years.” By contrast, biologists in 2012 readily sequenced the entire genome from Otzi, the frozen “ice man” who died in the Alps five thousand years ago.

After months of careful work, however, Schroeder’s team was able to extract DNA from the St. Martin individuals using a new procedure called whole-genome capture. Devised at Stanford University in California, this technique concentrates the degraded genes, providing enough material to sequence.

By comparing the results with a database from modern-day Africans, the researchers determined that all three people came from different parts of that continent. One of the men likely came from what is today northern Cameroon, while the other man and the woman may have originated in Ghana or Nigeria to the south.

Written by Randy McDonald

February 8, 2016 at 8:30 pm

[LINK] On the possible detection of gravitational waves from colliding black holes by LIGO

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Adrian Cho’s ScienceMag article notes in detail about something potentially astounding, something scheduled for official release on Friday the 11th but literally causing waves right now.

It’s just a rumor, but if specificity is any measure of credibility, it might just be right. For weeks, gossip has spread around the Internet that researchers with the Laser Interferometer Gravitational-Wave Observatory (LIGO) have spotted gravitational waves—ripples in space itself set off by violent astrophysical events. In particular, rumor has it that LIGO physicists have seen two black holes spiraling into each other and merging. But now, an email message that ended up on Twitter adds some specific numbers to those rumors. The author says he got the details from people who have seen the manuscript of the LIGO paper that will describe the discovery.

“This is just from talking to people who said they’ve seen the paper, but I’ve not seen the paper itself,” says Clifford Burgess, a theoretical physicist at McMaster University in Hamilton, Canada, and the Perimeter Institute for Theoretical Physics in nearby Waterloo. “I’ve been around a long time, so I’ve seen rumors come and go. This one seems more credible.”

According to Burgess’s email, which found its way onto Twitter as an image attached to a tweet from one of his colleagues, LIGO researchers have seen two black holes, of 29 and 36 solar masses, swirling together and merging. The statistical significance of the signal is supposedly very high, exceeding the “five-sigma” standard that physicists use to distinguish evidence strong enough to claim discovery. LIGO consists of two gargantuan optical instruments called interferometers, with which physicists look for the nearly infinitesimal stretching of space caused by a passing gravitational wave. According to Burgess’s email, both detectors spotted the black hole merger with the right time delay between them.

LIGO’s prime target has been the death spiral and merger not of two black holes, but of two neutron stars. However, Marc Kamionkowski, a theoretical physicist at Johns Hopkins University in Baltimore, Maryland, says the signal from the merger of more-massive black holes should be stronger and detectable from a greater distance. Other, less specific rumors suggest that LIGO has seen more than one source.

A commenter at another blog notes that the detection of gravitational waves is hugely important, perhaps the biggest development since the development of eyes hundreds of millions of years ago. I agree. If this is true, I think I know who’ll be getting a Nobel Prize in Physics, if not this year than next.

More to the point, it is decidedly cool that we now can apparently detect gravitational waves. Most speculatively, I wonder what such a collision of black holes would look like. Apparently three solar masses were dispersed into gravity waves. Would there have been electromagnetic radiation expelled, too?

Written by Randy McDonald

February 8, 2016 at 8:15 pm

[LINK] On a possible replacement of Europe’s ancient population of homo sapiens

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The Dragon’s Tales linked to the Cell paper “Pleistocene Mitochondrial Genomes Suggest a Single Major Dispersal of Non-Africans and a Late Glacial Population Turnover in Europe”. The abstract is eye-catching.

How modern humans dispersed into Eurasia and Australasia, including the number of separate expansions and their timings, is highly debated. Two categories of models are proposed for the dispersal of non-Africans: (1) single dispersal, i.e., a single major diffusion of modern humans across Eurasia and Australasia; and (2) multiple dispersal, i.e., additional earlier population expansions that may have contributed to the genetic diversity of some present-day humans outside of Africa. Many variants of these models focus largely on Asia and Australasia, neglecting human dispersal into Europe, thus explaining only a subset of the entire colonization process outside of Africa. The genetic diversity of the first modern humans who spread into Europe during the Late Pleistocene and the impact of subsequent climatic events on their demography are largely unknown. Here we analyze 55 complete human mitochondrial genomes (mtDNAs) of hunter-gatherers spanning ∼35,000 years of European prehistory. We unexpectedly find mtDNA lineage M in individuals prior to the Last Glacial Maximum (LGM). This lineage is absent in contemporary Europeans, although it is found at high frequency in modern Asians, Australasians, and Native Americans. Dating the most recent common ancestor of each of the modern non-African mtDNA clades reveals their single, late, and rapid dispersal less than 55,000 years ago. Demographic modeling not only indicates an LGM genetic bottleneck, but also provides surprising evidence of a major population turnover in Europe around 14,500 years ago during the Late Glacial, a period of climatic instability at the end of the Pleistocene.

Written by Randy McDonald

February 8, 2016 at 8:08 pm

[LINK] “DNA from Neandertal relative may shake up human family tree”

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I came across very recently Ann Gibbons’ September 2015 Sciencemag article noting yet another remarkable turn in the history of the hominid family.

In a remarkable technical feat, researchers have sequenced DNA from fossils in Spain that are about 300,000 to 400,000 years old and have found an ancestor—or close relative—of Neandertals. The nuclear DNA, which is the oldest ever sequenced from a member of the human family, may push back the date for the origins of the distinct ancestors of Neandertals and modern humans, according to a presentation here yesterday at the fifth annual meeting of the European Society for the study of human evolution.

Ever since researchers first discovered thousands of bones and teeth from 28 individuals in the mid-1990s from Sima de los Huesos (“pit of bones”), a cave in the Atapuerca Mountains of Spain, they had noted that the fossils looked a lot like primitive Neandertals. The Sima people, who lived before Neandertals, were thought to have emerged in Europe. Yet their teeth, jaws, and large nasal cavities were among the traits that closely resembled those of Neandertals, according to a team led by paleontologist Juan-Luis Arsuaga of the Complutense University of Madrid. As a result, his team classified the fossils as members of Homo heidelbergensis, a species that lived about 600,000 to 250,000 years ago in Europe, Africa, and Asia. Many researchers have thought H. heidelbergensis gave rise to Neandertals and perhaps also to our species, H. sapiens, in the past 400,000 years or so.

But in 2013, the Sima fossils’ identity suddenly became complicated when a study of the maternally inherited mitochondrial DNA (mtDNA) from one of the bones revealed that it did not resemble that of a Neandertal. Instead, it more closely matched the mtDNA of a Denisovan, an elusive type of extinct human discovered when its DNA was sequenced from a finger bone from Denisova Cave in Siberia. That finding was puzzling, prompting researchers to speculate that perhaps the Sima fossils had interbred with very early Denisovans or that the “Denisovan” mtDNA was the signature of an even more ancient hominin lineage, such as H. erectus. At the time, researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who had obtained the mtDNA announced that they would try to sequence the nuclear DNA of the fossils to solve the mystery.

After 2 years of intense effort, paleogeneticist Matthias Meyer of the Max Planck Institute for Evolutionary Anthropology has finally sequenced enough nuclear DNA from fossils of a tooth and a leg bone from the pit to solve the mystery. The task was especially challenging because the ancient DNA was degraded to short fragments, made up of as few as 25 to 40 single nucleotides. (Nucleotides—also known as base pairs—are the building blocks of DNA.) Although he and his colleagues did not sequence the entire genomes of the fossils, Meyer reported at the meeting that they did get 1 million to 2 million base pairs of ancient nuclear DNA.

They scanned this DNA for unique markers found only in Neandertals or Denisovans or modern humans, and found that the two Sima fossils shared far more alleles—different nucleotides at the same address in the genome—with Neandertals than Denisovans or modern humans. “Indeed, the Sima de los Huesos specimens are early Neandertals or related to early Neandertals,” suggesting that the split of Denisovans and Neandertals should be moved back in time, Meyer reported at the meeting.

Researchers at the meeting were impressed by this new breakthrough in ancient DNA research. “This has been the next frontier with ancient DNA,” says evolutionary biologist Greger Larson of the University of Oxford in the United Kingdom.

Written by Randy McDonald

February 8, 2016 at 8:04 pm


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