понедельник, 27 мая 2019 г.

Chemistry of stars sheds new light on the Gaia Sausage

Chemical traces in the atmospheres of stars are being used to uncover new information about a galaxy, known as the Gaia Sausage, which was involved in a major collision with the Milky Way billions of years ago.

Chemistry of stars sheds new light on the Gaia Sausage
Credit: University of Birmingham

Astrophysicists at the University of Birmingham in collaboration with colleagues at European institutions in Aarhus, Bologna and Trieste, have been studying evidence of the chemical composition of stars in this area of the Milky Way to try to pinpoint more accurately the age of the smaller galaxy.

The Gaia Sausage was identified last year by an international team using information from the European Space Agency’s Gaia satellite. Its merger with the Milky Way, estimated to have occurred about 10 billion years ago, is thought to have contributed to the shape of the Milky Way that we recognise today.

Using only the information about the chemical traces of Gaia Sausage stars coming from the international APOGEE astronomical survey, the Birmingham researchers have pinpointed more precisely the age of the galaxy. By developing detailed models of the production, or nucleosynthesis of chemical elements by all kinds of stars and supernovae in the cosmos, they estimate the Sausage was formed around 12.5bn years ago — 2.5bn years older than suggested by previous estimates.

«Elements interact with light in different ways and so by studying the properties of light from the stars, we can infer the chemical make-up of those stars,» explains Fiorenzo Vincenzo, in the School of Physics and Astronomy at the University of Birmingham.

«All chemical elements heavier than helium are produced by stars via thermonuclear burning deep in the heart of the star. Different chemical elements are typically synthesised by different kinds of stars in the cosmos. The oxygen atoms that are so important for life processes, for example, were deposited in the interstellar medium by many successive generations of massive stars until they were incorporated by our planet about 4.5 billion years ago. We can measure the relative proportion of different chemical traces in the atmosphere of stars and use this measurement as a clock to determine their age.»

Calculating the ages of stars accurately is a complex process and the technique used by the Birmingham team provides one piece of the puzzle. The next step will be to cross reference the chemical data with evidence from other techniques, such as studying the relative speeds at which stars move — a project also underway at the University of Birmingham.

The merger between the two galaxies seems to have produced another effect, too. The team spotted a gap in the age distribution of stars in the Milky Way, that occurred at the same time as the merger, suggesting that the collision caused an interruption in star formation within the Milky Way.

«We speculate that the turbulence and heating caused by the merger of the Gaia Sausage with the Milky Way could have prevented the formation of stars at this time,» says Dr Vincenzo. «However to confirm this we would need even more precise measurements of the ages of the stars in the Milky Way and in the smaller galaxy.»

The study is published in Monthly Notices of the Royal Astronomical Society and is part of the Asterochronometry project, funded by the European Research Council and led by the University of Birmingham. The main aim of the project is to pinpoint precise and accurate stellar ages — a keystone for understanding the assembly history of our galaxy.

In this study, the team focused on the chemical traces left by three elements — iron, silicon and magnesium. The next step will be to incorporate measurements from other elements to build an increasingly accurate picture.

Source: University of Birmingham [May 23, 2019]



Climate change may make the arctic tundra a drier landscape

With climate change, the Arctic tundra is likely to become drier. Lakes may shrink in size and smaller lakes may even disappear according to a new Dartmouth study. In western Greenland, Kangerlussuaq experienced a 28 percent decrease in the number of smaller lakes (those less than 10,000 square meters) and a 20 percent decrease in total area from 1969 to 2017. Many of the lakes that had disappeared in 1969 have since become vegetated. The findings are published in the Journal of Geophysical Research: Biogeosciences.

Climate change may make the arctic tundra a drier landscape
Imagery time series example demonstrating large lake (top row) and small lake (bottom row) area change at different
locations across the study region of Kangerlussuaq, Greenland, from 1969 to 2017. Blue contours indicate
delineated water body margins. Image is Figure 3 from the study [Credit: Figure prepared
by Rebecca Finger Higgens. Imagery courtesy of Planet Labs, Inc.]

«Lake drying may be one of the most significant consequences of Arctic climate change given that the majority of the world’s lakes are in high latitudes,» explained lead author Rebecca Finger Higgens, a graduate student in the ecology, evolution, ecosystems and society program at Dartmouth. «Much of the drying of lakes in Kangerlussuaq has been occurring from 1985 until now, a period during which we’ve also seen a 2.5 Celsius increase in the mean annual temperature. Our results demonstrate that warmer temperatures in western Greenland over the past 30 years have accelerated lake decline,» she added.

Finger Higgens first noticed that the Arctic landscape seemed to be getting drier in 2015 while doing fieldwork outside of Kangerlussuaq, Greenland. From 2015 to 2017, she served as a Joint Science Education Program (JSEP) graduate fellow during which she spent over six months conducting research in Kangerlussuaq. She started compiling collections of satellite and aerial imagery of lakes in Greenland gathered in the 1960s and 1980s and weather data to track changes over time.

Images of lakes in Kangerlussuaq were sourced from: declassified satellite CORONA imagery from the Cold War, which is available through the U.S. Geological Survey; an aerial survey by the Danish Government in Greenland, which is available through the National Oceanic and Atmospheric Administration; and satellite imagery from summer 2017 by Planet Labs, Inc. Temperature and precipitation data for Kangerlussuaq obtained by the Danish Meteorological Institute during 1971 to 2017 was also used.

In analyzing the imagery, the team wanted to determine why some lakes visible in 1969 weren’t visible in 2017. For a lake to be classified as disappeared, it had to have dried (be vegetated or non-vegetated) and be smaller than 100 square meters. The team found three possible reasons as to why some lakes weren’t visible in 2017: vegetation had come in and recolonized the area; the lake water was still present but too small to be detected by their threshold; or the lake remained but was just dry and not vegetated. Most of the lakes in the study which had disappeared were dry and vegetated.

While smaller lakes in Kangerlussuaq appeared to be especially susceptible to lake decline, larger lakes also saw a decline with a 21 percent decrease in lake count and a 2 percent decrease in surface area. The rapid thawing of permafrost may contribute to the draining of some larger lakes in the future. Warmer winters and drier summers are likely to accelerate losses in lakes, as the researchers found that evapotranspiration rates were higher during June, July and August. The study explains that these rates may be «exacerbated by longer snow- and ice-free periods during the summer.»

«As smaller lakes and wetlands disappear in the Arctic, the habitat of aquatic organisms and other animals is likely to be jeopardized,» said Finger Higgens. «The Arctic is home to many bird species that migrate north to breed, especially waterfowl. With declines in wetlands, we may see some declines in goose populations in this area.»

In addition, a drier Arctic may also increase the vulnerability to soil erosion, insect outbreaks, tundra fires and other phenomenon associated with drought-like conditions.

Source: Dartmouth College [May 23, 2019]



Widespread permafrost degradation seen in high Arctic terrain

Rapid changes in terrain are taking place in Canada’s high Arctic polar deserts due to increases in summer air temperatures.

Widespread permafrost degradation seen in high Arctic terrain
Due to record summer temperatures in recent years, high Arctic polar terrain is changing
[Credit: Melissa Ward Jones]

A McGill-led study published recently in Environmental Research Letters presents close to 30 years of aerial surveys and extensive ground mapping of the Eureka Sound Lowlands area of Ellesmere and Axel Heiberg Islands located at approximately 80 °N.

The research focuses on a particular landform (known as a retrogressive thaw slump) that develops as the ice within the permafrost melts and the land slips down in a horseshoe-shaped feature. The presence of these landforms is well documented in the low Arctic.

But due to the extremely cold climate in high Arctic polar deserts (where average annual ground and air temperatures are -16.5 °C/2.3 °F, and -19.7 °C /-3.46 °F, respectively), and the fact that the permafrost is over 500 metres (or about 1/3 of a mile) thick, it had been assumed this landscape was stable. But the McGill-led research team found that this has not been the case.

«Our study suggests that the warming climate in the high Arctic, and more specifically the increases in summer air temperatures that we have seen in recent years, are initiating widespread changes in the landscape,» says Melissa Ward Jones, the study’s lead author and a PhD candidate in McGill’s Department of Geography.

Widespread permafrost degradation seen in high Arctic terrain
Scientists from McGill University have been mapping the high Arctic polar deserts for almost thirty years. In the past
few years, as the permafrost melts, they have seen an increase and spread of landslide-like features in an area
where they had believed extremely cold temperatures would ensure the stability of the land
[Credit: Melissa Ward Jones]

The research team noted that:

— There has been a widespread development of retrogressive thaw slumps in high Arctic polar deserts over a short period, particularly during the unusually warm summers of 2011, 2012 and 2015;

— That the absence of vegetation and layers of organic soil in these polar deserts make permafrost in the area particularly vulnerable to increases in summer air temperatures;

— Despite its relatively short duration, the thaw season (which lasts for just 3-6 weeks a year) initially drives the development of slumps and their later expansion in size, as their headwall retreats; and

— Over a period of a few years after the initiation of slumps, study results suggest various factors related to terrain (e.g. slope) become more important than air temperature in maintaining active slumps.

In recent years, high summer temperatures have started melting the ice in the permafrost. 

As a result, land forms are changing unexpectedly [Credit: McGill University]

«Despite the cold polar desert conditions that characterize much of the high Arctic, this research clearly demonstrates the complex nature of ice-rich permafrost systems and climate-permafrost interaction,» adds Wayne Pollard, a professor in McGill’s Department of Geography and co-author on the study. «Furthermore, it raises concerns about the over simplification of some studies that generalize about the links between global warming and permafrost degradation.»

Author: Katherine Gombay | Source: McGill University [May 23, 2019]



New studies increase confidence in NASA’s measure of Earth’s temperature

A new assessment of NASA’s record of global temperatures revealed that the agency’s estimate of Earth’s long-term temperature rise in recent decades is accurate to within less than a tenth of a degree Fahrenheit, providing confidence that past and future research is correctly capturing rising surface temperatures.

New studies increase confidence in NASA's measure of Earth's temperature
2014-2018, averaged on this map, were the warmest years in the modern record compared to GISTEMP’s
1951-1980 baseline. The areas in red experienced warmer than normal temperatures, while
the areas in blue were cooler than normal during this period [Credit: NASA]

The most complete assessment ever of statistical uncertainty within the GISS Surface Temperature Analysis (GISTEMP) data product shows that the annual values are likely accurate to within 0.09 degrees Fahrenheit (0.05 degrees Celsius) in recent decades, and 0.27 degrees Fahrenheit (0.15 degrees C) at the beginning of the nearly 140-year record.

This data record, maintained by NASA’s Goddard Institute for Space Studies (GISS) in New York City, is one of a handful kept by major science institutions around the world that track Earth’s temperature and how it has risen in recent decades. This global temperature record has provided one of the most direct benchmarks of how our home planet’s climate has changed as greenhouse gas concentrations rise.

The study also confirms what researchers have been saying for some time now: that Earth’s global temperature increase since 1880 — about 2 degrees Fahrenheit, or a little more than 1 degree Celsius — cannot be explained by any uncertainty or error in the data. Going forward, this assessment will give scientists the tools to explain their results with greater confidence.

GISTEMP is a widely used index of global mean surface temperature anomaly — it shows how much warmer or cooler than normal Earth’s surface is in a given year. «Normal» is defined as the average during a baseline period of 1951-80.

NASA uses GISTEMP in its annual global temperature update, in partnership with the National Oceanic and Atmospheric Administration. (In 2019, NASA and NOAA found that 2018 was the fourth-warmest year on record, with 2016 holding the top spot.) The index includes land and sea surface temperature data back to 1880, and today incorporates measurements from 6,300 weather stations, research stations, ships and buoys around the world.

Previously, GISTEMP provided an estimate of uncertainty accounting for the spatial gaps between weather stations. Like other surface temperature records, GISTEMP estimates the temperatures between weather stations using data from the closest stations, a process called interpolation. Quantifying the statistical uncertainty present in those estimates helped researchers to be confident that the interpolation was accurate.

«Uncertainty is important to understand because we know that in the real world we don’t know everything perfectly,» said Gavin Schmidt, director of GISS and a co-author on the study. «All science is based on knowing the limitations of the numbers that you come up with, and those uncertainties can determine whether what you’re seeing is a shift or a change that is actually important.»

The study found that individual and systematic changes in measuring temperature over time were the most significant source of uncertainty. Also contributing was the degree of weather station coverage. Data interpolation between stations contributed some uncertainty, as did the process of standardizing data that was collected with different methods at different points in history.

After adding these components together, GISTEMP’s uncertainty value in recent years was still less than a tenth of a degree Fahrenheit, which is «very small,» Schmidt said.

The team used the updated model to reaffirm that 2016 was very probably the warmest year in the record, with an 86.2 percent likelihood. The next most likely candidate for warmest year on record was 2017, with a 12.5 percent probability.

«We’ve made the uncertainty quantification more rigorous, and the conclusion to come out of the study was that we can have confidence in the accuracy of our global temperature series,» said lead author Nathan Lenssen, a doctoral student at Columbia University. «We don’t have to restate any conclusions based on this analysis.»

Another recent study evaluated GISTEMP in a different way that also added confidence to its estimate of long-term warming. A paper published in March 2019, led by Joel Susskind of NASA’s Goddard Space Flight Center, compared GISTEMP data with that of the Atmospheric Infrared Sounder (AIRS), onboard NASA’s Aqua satellite.

GISTEMP uses air temperature recorded with thermometers slightly above the ground or sea, while AIRS uses infrared sensing to measure the temperature right at the Earth’s surface (or «skin temperature») from space. The AIRS record of temperature change since 2003 (which begins when Aqua launched) closely matched the GISTEMP record.

Comparing two measurements that were similar but recorded in very different ways ensured that they were independent of each other, Schmidt said. One difference was that AIRS showed more warming in the northernmost latitudes.

«The Arctic is one of the places we already detected was warming the most. The AIRS data suggests that it’s warming even faster than we thought,» said Schmidt, who was also a co-author on the Susskind paper.

Taken together, Schmidt said, the two studies help establish GISTEMP as a reliable index for current and future climate research.

«Each of those is a way in which you can try and provide evidence that what you’re doing is real,» Schmidt said. «We’re testing the robustness of the method itself, the robustness of the assumptions, and of the final result against a totally independent data set.»

In all cases, he said, the resulting trends are more robust than what can be accounted for by any uncertainty in the data or methods.

Author: Jessica Merzdorf | Source: NASA’s Goddard Space Flight Center [May 23, 2019]



Climate change affects the genetic diversity of a species

What effects does climate change have on the genetic diversity of living organisms? In a study led by Charité — Universitätsmedizin Berlin, an international team of researchers studied the genome of the alpine marmot, an ice-age remnant that now lives in large numbers in the high altitude Alpine meadow. Results were unexpected: the species was found to be the least genetically diverse of any wild mammal studied to date. An explanation was found in the marmots genetic past. The alpine marmot has lost its genetic diversity during ice-age related climate events and been unable to recover its diversity since. Results from this study have been published in the journal Current Biology.

Climate change affects the genetic diversity of a species
Credit: Carole & Denis Favre-Bonvin

A large rodent from the squirrel family, the alpine marmot lives in the high-altitude mountainous terrain found beyond the tree line. An international team of researchers has now successfully deciphered the animal’s genome and found the individual animals tested to be genetically very similar. In fact, the animal’s genetic diversity is lower than that of any other wild mammal whose genome has been genetically sequenced.
«We were very surprised by this finding. Low genetic diversity is primarily found among highly endangered species such as, for instance, the mountain gorilla. Population numbers for the alpine marmot, however, are in the hundreds of thousands, which is why the species is not considered to be at risk,» explains Prof. Dr. Markus Ralser, the Director of Charité’s Institute of Biochemistry and the investigator with overall responsibility for the study, which was co-led by the Francis Crick Institute.

As the alpine marmot’s low genetic diversity could not be explained by the animal’s current living and breeding habits, the researchers used computer-based analysis to reconstruct the marmot’s genetic past. After combining the results of comprehensive genetic analyses with data from fossil records, the researchers came to the conclusion that the alpine marmot lost its genetic diversity as a result of multiple climate-related adaptations during the last ice age.

Climate change affects the genetic diversity of a species
Credit: Carole & Denis Favre-Bonvin

One of these adaptations occurred during the animal’s colonization of the Pleistocene steppe at the beginning of the last ice age (between 110,000 and 115,000 years ago). A second occurred when the Pleistocene steppe disappeared again towards the end of the ice age (between 10,000 and 15,000 years ago). Since then, marmots have inhabited the high-altitude grasslands of the Alps, where temperatures are similar to those of the Pleistocene steppe habitat.
The researchers found evidence to suggest that the marmot’s adaptation to the colder temperatures of the Pleistocene steppe resulted in longer generation time and a decrease in the rate of genetic mutations. These developments meant that the animals were unable to effectively regenerate their genetic diversity. Overall results suggest that the rate of genome evolution is exceptionally low in alpine marmots.

Commenting on the significance of their results, Prof. Ralser says: «Our study shows that climate change can have extremely long-term effects on the genetic diversity of a species. This had not previously been shown in such clear detail. When a species displays very little genetic diversity, this can be due to climate events which occurred many thousands of years ago,» He adds: «It is remarkable that the alpine marmot managed to survive for thousands of years despite its low genetic diversity.» After all, a lack of genetic variation can mean a reduced ability to adapt to change, rendering the affected species more susceptible to both diseases and altered environmental conditions — including changes in the local climate.»

Climate change affects the genetic diversity of a species
Credit: Carole & Denis Favre-Bonvin

Summarizing the study’s findings, Prof. Ralser explains: «We should take the results of the study seriously, as we can see similar warnings from the past. In the 19th century, the passenger pigeon was one of the most abundant species of land birds in the Northern Hemisphere, yet, it was completely wiped out within just a few years. It is possible that low genetic diversity played a role in this.» Outlining his plans for further research, he adds: «An important next step would be to study other animals more closely which, like the alpine marmot, managed to survive the ice age. These animals might be trapped in a similar state of low genetic diversity. Currently, estimates of a particular species’ extinction risk are primarily based on the number of animals capable of breeding. We ought to reconsider whether this should be the only criterion we use.»

Source: Charité – Universitätsmedizin Berlin [May 23, 2019]



Scientists create new standard genome for heavily studied worm

A new Cornell University-led study finds that the genome for a widely researched worm, on which countless studies are based, was flawed. Now, a fresh genome sequence will set the record straight and improve the accuracy of future research.

Scientists create new standard genome for heavily studied worm
The nematode worm Caenorhabditis elegans. Three life stages of C. elegans are shown: an adult hermaphrodite,
a smaller larva, and eleven newly laid eggs (with embryos developing inside them). These are all on a lawn
of Escherichia coli bacteria (being eaten by the worms as food). The fully grown adult is roughly
1 millimetre long [Credit: Marie-Anne Felix, Ecole Normale Superieure]

When scientists study the genetics of an organism, they start with a standard genome sequenced from a single strain that serves as a baseline. It’s like a chess board in a chess game: every board is fundamentally the same.

One model organism that scientists use in research is a worm called Caenorhabditis elegans. The worm — the first multicellular eukaryote (animal, plant or fungus) to have its genome sequenced — is easy to grow and has simple biology with no bones, heart or circulatory system. At the same time, it shares many genes and molecular pathways with humans, making it a go-to model for studying gene function, drug treatments, aging and human diseases such as cancer and diabetes.

Genetic studies of C. elegans were based on a single strain, called N2, which researchers have ordered for decades from the C. elegans stock center at the University of Minnesota. Though people tried to uphold a common standard, individual labs grew N2 strains on their own, which led to morphing.

«Over the last decade, with more advanced genetic experiments using high levels of DNA sequencing, scientists were alarmed to discover that there is no longer a single laboratory strain that everyone was using,» said Erich Schwarz, assistant research professor in the Department of Molecular Biology and Genetics. «Over 40 years there have arisen many different N2 strains; we can’t rely on any one of them to do experiments.»

Schwarz is a senior author of a new study published in Genome Research that describes a single genetically clean strain, called VC2010, where each individual is truly identical. Schwarz and colleagues from the University of Tokyo, Stanford University, the University of British Columbia and the University of Minnesota used cutting-edge techniques to sequence VC2010’s genome and create a new standard.

As part of the study, the researchers compared VC2010 to the original N2 genome. They expected a near-perfect match, but got a surprise. «Along with the 100 million nucleotides we expected to see, we discovered an extra 2 million nucleotides, an extra two percent of the genome,» that was hidden in the original, likely due to limitations of old technology, Schwarz said.

Schwarz added that similar issues are likely occurring in the standard genomes of other organisms, including humans. «It shows us that having the true complete DNA of an animal is not as easy as we thought it was,» he said.

Other labs have begun using modern sequencing tools to reassess other genomes, which has implications for synthetic biology, where scientists are creating life — such as bacteria — from scratch. «Having a really good DNA sequence is an important baseline,» Schwarz said.

Author: Krishna Ramanujan | Source: Cornell University [May 23, 2019]



Exploring secret places at ‘Brimham Rocks’ Ice Age Rock Features, Yorkshire,...

Exploring secret places at ‘Brimham Rocks’ Ice Age Rock Features, Yorkshire, 27.5.19.

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Oldest meteorite collection on Earth found in one of the driest places

Earth is bombarded every year by rocky debris, but the rate of incoming meteorites can change over time. Finding enough meteorites scattered on the planet’s surface can be challenging, especially if you are interested in reconstructing how frequently they land. Now, researchers have uncovered a wealth of well-preserved meteorites that allowed them to reconstruct the rate of falling meteorites over the past two million years.

Oldest meteorite collection on Earth found in one of the driest places
The L6 ordinary chondrite El Medano 128, a 556 g meteorite recovered in the Atacama Desert
[Credit: CCJ-CNRS, P. Groscaux]

«Our purpose in this work was to see how the meteorite flux to Earth changed over large timescales — millions of years, consistent with astronomical phenomena,» says Alexis Drouard, Aix-Marseille Université, lead author of the new paper in Geology.
To recover a meteorite record for millions of years, the researchers headed to the Atacama Desert. Drouard says they needed a study site that would preserve a wide range of terrestrial ages where the meteorites could persist over long time scales.

Oldest meteorite collection on Earth found in one of the driest places
Large meteorite found in the Atacama Desert
[Credit: Jerome Gattacceca (CEREGE)]

While Antarctica and hot deserts both host a large percentage of meteorites on Earth (about 64% and 30%, respectively), Drouard says, «Meteorites found in hot deserts or Antarctica are rarely older than half a million years.» He adds that meteorites naturally disappear because of weathering processes (e.g., erosion by wind), but because these locations themselves are young, the meteorites found on the surface are also young.
«The Atacama Desert in Chile, is very old ([over] 10 million years),» says Drouard. «It also hosts the densest collection of meteorites in the world.»

Oldest meteorite collection on Earth found in one of the driest places
Meteorite with thin, dark, fusion crust in the Atacama Desert
[Credit: Jerome Gattacceca (CEREGE)]

The team collected 388 meteorites and focused on 54 stony samples from the El Médano area in the Atacama Desert. Using cosmogenic age dating, they found that the mean age was 710,000 years old. In addition, 30% of the samples were older than one million years, and two samples were older than two million. All 54 meteorites were ordinary chondrites, or stony meteorites that contain grainy minerals, but spanned three different types.
«We were expecting more ‘young’ meteorites than ‘old’ ones (as the old ones are lost to weathering),» says Drouard. «But it turned out that the age distribution is perfectly explained by a constant accumulation of meteorites for millions years.» The authors note that this is the oldest meteorite collection on Earth’s surface.

Oldest meteorite collection on Earth found in one of the driest places
Meteorite recovery campaign in the Atacama Desert, Nov. 2017
[Credit: Katherine Joy (University of Manchester)]

Drouard says this terrestrial crop of meteorites in the Atacama can foster more research on studying meteorite fluxes over large time scales. «We found that the meteorite flux seems to have remained constant over this [two-million-year] period in numbers (222 meteorites larger than 10 g per squared kilometer per million year), but not in composition,» he says. Drouard adds that the team plans to expand their work, measuring more samples and narrowing in on how much time the meteorites spent in space. «This will tell us about the journey of these meteorites from their parent body to Earth’s surface.»

Source: Geological Society of America [May 23, 2019]



Using computer simulations to discover where Neanderthals lived

Archaeologist Fulco Sherjon has used computer simulations to identify where and how Neanderthals lived in West Europe. What stood out was that they probably had lots of children and lived in smaller groups than was previously thought. Ph.D. defense on 28 May.

Using computer simulations to discover where Neanderthals lived
Credit: Leiden University

The Neanderthals lived in Europe and Asia some 400,000 to 40,000 years ago. Many questions remain about this extinct human species, which lived at the same time as early modern humans. In which areas did they live, for instance? And how did they live?
HomininSpace, the computer program that archaeologist Fulco Sherjon developed, gives some pointers. He got the program to look at whether the Neanderthals lived in England. «We know they were there in some periods, but not whether they were there in others. The conclusion was that it is unlikely that they were not in England in those periods,» he explains. In other words: it is highly likely that they were there in those periods too.

Simulation of 3.3 billion Neanderthal years

Scherjon entered the data from 83 Neanderthal sites in West Europe into Homininspace, together with 470 exact datings of a Neanderthal presence. The simulation area was mainly in France because this is where most of the finds have been made. The system compared this information with the simulation results.

The program carried out about 40,000 simulations, simulating almost 3.3 billion Neanderthal years. There are other Neanderthal simulation programs, but what makes HomininSpace unique is that it looks for the model that produces the best matches, Scherjon explains. «The program uses this to produce the most probable answer. Rather than say: «this is what the Neanderthals were like» it says: «it’s probable that the Neanderthals were here at that time or lived like this.»‘

Neanderthals had high birth rate

What the simulation results also suggest is that in the span of their relatively short lives, the Neanderthals probably had plenty of offspring. «According to my model, a birth rate of 40 percent is probable. That means 40 percent of the women have a baby in one year. That is quite high. To investigate this in more detail, you could look at whether this figure is consistent with other archaeological data. Certain lines on the teeth show moments of stress, for instance. If a woman has had six children, and thus experienced labor pain six times, you may be able to see this on her teeth.»

Small, vulnerable groups

It also looked likely that the Neanderthals moved around in relatively small groups. «The literature talks about groups of about 25 in size,» Scherjon explains, «but the simulations suggest that a figure of between 10 and 12 people is more likely. Such groups probably consisted of about two to three adult women, two to three adult men and a few children. This is surprising because such small groups are vulnerable.»

Other researchers

Scherjon now wants to make HomininSpace available to others. «The program is generic in design, so you can also use it to analyze hominids or top predators—animals at the top of the food chain. We are going to publish Homininspace open access, via the University and OpenABM, a website where you can share academic models. I definitely hope that other researchers will use it.»

Source: Leiden University [May 23, 2019]



Dolphin study reveals the genes essential for species’ survival

UNSW scientists have added to the growing body of research into genetic markers that are important for animal conservation.

Dolphin study reveals the genes essential for species' survival
Bottlenose dolphins of Shark Bay, Western Australia [Credit: Ewa Krzyszczyk,
Georgetown University]

Certain types of immune genes may be particularly important for the survival of dolphins, a new study by an international team of researchers that investigated genetic diversity of dolphin populations reveals.

Knowing which genes are essential for helping dolphin populations survive has important implication for conservation: it is often difficult to monitor changes in population sizes of wild animal populations, especially long-lived dolphins, who spend most of their time under water. This also makes it hard to detect whether these populations are threatened—so identifying genes that are essential for survival could offer an indicator for potential threats to the viability of populations.

«Genetic diversity is crucial for animals to adapt to a changing environment—for example, diverse genes can help populations defend against diseases and tolerate climate change—but not all genetic diversity is equally important,» says lead author Dr. Oliver Manlik, who is an Assistant Professor at the United Arab Emirates University and conjoint faculty member of UNSW Science.

Until recently, most studies that assessed genetic diversity in wild animals used «adaptively neutral» genetic markers that don’t offer any clues as to whether animals can adapt to a changing environment. Adaptively neutral genetic markers are gene variants that usually do not have any particular function, and are neither beneficial nor harmful to individuals or populations. Such genetic variants are, therefore, not so important for adaptation or survival.

«In order to identify genetic variants that are necessary for animals to adapt and to survive, it is important to focus on genes that are linked to ecologically important traits,» Dr. Manlik says.

«One such group of genes are the immune genes of the major histocompatibility complex (MHC), which play a critical role in recognizing pathogens and starting an immune defense.»

In their new study, published in the international journal Ecology and Evolution, the scientists compared «adaptively neutral» genetic diversity and genetic diversity of MHC genes in two bottlenose dolphin populations in Western Australia. One of the two dolphin populations, in Shark Bay, was previously assessed to be stable. In contrast, the other, much smaller population near Bunbury was forecast to decline, unless it is supported by immigrants from other populations nearby. This was shown in two previous studies, which were also led by Dr. Manlik.

«In the study published today, we found that the large, stable population in Shark Bay exhibited much greater MHC diversity than the smaller, less stable population,» Dr. Manlik says.

«On the other hand, there was almost no difference between the two populations with respect to neutral genetic diversity.»

Professor Michael Krützen at the University of Zurich and co-author of the study says the Shark Bay dolphins, which carry greater immunogenetic diversity than their counterparts off Bunbury, are likely more robust to natural or human-induced changes to the coastal ecosystem.

«In other words, having greater MHC diversity may offer extra protection to these dolphins, but certainly does not make them invincible to the many threats they face.»

The findings of the study also suggest that MHC diversity could be a useful indicator of population health of these dolphins and possibly other vertebrates who also have MHC genes.

Professor Bill Sherwin from UNSW, who supervised the study, says the results should be interpreted with caution, given the team only compared two populations.

«However, our results add to a growing number of studies that underscore the usefulness of MHC as a potentially suitable genetic marker for animal conservation.»

«If we want to identify genetic indicators for wildlife conservation, we should monitor adaptive genes, such as MHC genes, that are important for adaptation and survival of populations,» Dr. Manlik concludes.

Source: University of New South Wales [May 24, 2019]



How corn’s ancient ancestor swipes left on crossbreeding

Determining how one species becomes distinct from another has been a subject of fascination dating back to Charles Darwin. New research led by Carnegie’s Matthew Evans and published in Nature Communications elucidates the mechanism that keeps maize distinct from its ancient ancestor grass, teosinte.

How corn's ancient ancestor swipes left on crossbreeding
A teosinte plant growing in a corn field on the Stanford University campus
[Credit: Yongxian Lu]

Speciation requires isolation. Sometimes this isolation is facilitated by geography, such as mountains chains or islands that divide two populations and prevent them from interbreeding until they become different species. But in other instances, the barriers separating species are physiological factors that prevent them from successfully mating, or from producing viable offspring.

«In plants, this genetic isolation can be maintained by features that prevent the ‘male’ pollen of one species from successfully fertilizing the ‘female’ pistil of another species,» explained Evans.

About 9,000 years ago, maize, or corn, was domesticated from teosinte in the Balsas River Valley of Mexico. Some populations of the two grasses are compatible for breeding. But others grow in the same areas and flower at the same time, but rarely produce hybrids.

It was known that a cluster of genes called Tcb1-s is one of three that confers incompatibility between these rarely hybridizing maize and teosinte populations. Unlike the other two, it is found almost exclusively in wild teosinte. It contains both male and female genes that encode wild teosinte’s ability to reject maize pollen.

In sexually compatible plants, the pollen, which is basically a sperm delivery vehicle, lands on the pistil and forms a tube that elongates and burrows down into the ovary, where the egg is fertilized. But that’s not what happens when maize pollen lands on the pistil, or silk, of a wild teosinte plant.

Evans and his colleagues—Carnegie’s Yongxian Lu (the first author), Samuel Hokin, and Thomas Hartwig, along with Jerry Kermicle of the University of Wisconsin Madison—demonstrated that the Tcb1-female gene encodes a protein that is capable of modifying cell walls, likely making maize pollen tubes less elastic and thus preventing them from reaching the teosinte eggs. When these tubes can’t stretch all the way to the eggs, fertilization can’t occur, and hybrids won’t be possible.

What’s more, because teosinte pollen can fertilize itself, the researchers think that the Tcb1-male genes encode an ability that allows teosinte pollen to overcome this pollen tube barrier building.

«Most plants that depend on wind and water, not birds or insects, for pollination have low species diversity,» said Evans. «But not grasses, which makes their evolutionary history particularly interesting.»

Source: Carnegie Institution for Science [May 24, 2019]



New research shows that mites and ticks are close relatives

Scientists from the University of Bristol and the Natural History Museum in London have reconstructed the evolutionary history of the chelicerates, the mega-diverse group of 110,000 arthropods that includes spiders, scorpions, mites and ticks.

New research shows that mites and ticks are close relatives
There is a phenomenal diversity of mites (as shown by these two examples),
and ticks are close relatives [Credit: David Walter]

They found, for the first time, genomic evidence that mites and ticks do not constitute two distantly related lineages, rather they are part of the same evolutionary line. This now makes them the most diverse group of chelicerates, changing our perspective on their biodiversity.

Arthropoda, or jointed-legged animals, make up the majority of animal biodiversity. They both pollinate (bees) and destroy our crops (locusts), are major food sources (shrimps and crabs), and are vectors of serious diseases like malaria and Lyme disease (mosquitoes and ticks).

Arthropods are ancient and fossils show that they have been around for more than 500 million years. The secret of their evolutionary success, which is reflected in their outstanding species diversity, is still unknown. To clarify what makes arthropod so successful we first need to understand how the different arthropod lineages relate to each other.

Co-author of the study, Professor Davide Pisani, from the University of Bristol’s School of Earth Sciences and Biological Sciences, said: «Finding that mites and ticks constitute a single evolutionary lineage is really important for our understanding of how biodiversity is distributed within Chelicerata.

«Spiders, with more than 48,000 described species, have long been considered the most biodiverse chelicerate lineage, but 42,000 mite and 12,000 tick species have been described. So, if mites and ticks are a single evolutionary entity rather than two distantly related ones, they are more diverse than the spiders.»

Dr Greg Edgecombe of the Natural History Museum London added: «Because of their anatomical similarities it has long been suspected that mites and ticks form a natural evolutionary group, which has been named Acari. However, not all anatomists agreed, and genomic data never found any support for this idea before.»

Lead author, Dr Jesus Lozano Fernandez, from Bristol’s School of Biological Sciences, said: «Spiders are iconic terrestrial animals that have always been part of the human imagination and folklore, representing mythological and cultural symbols, as well as often being objects of inner fears or admiration.

«Spiders have long been considered the most biodiverse chelicerate lineage, but our findings show that Acari is, in fact, bigger.»

In order to come up with their findings, the researchers used an almost even representation of mites and ticks (10 and 11 species, respectively), the most complete species-level sampling at the genomic level for these groups so far.

Dr Lozano-Fernandez added: «Regardless of the methods we used, our results converge on the same answer — mites and ticks really do form a natural group. Evolutionary trees like the one we’ve reconstructed provide us with the background information we need to interpret processes of genomic change.

«Our genealogical tree can now be used as the foundation for studies using comparative genomics to address problems of potential biomedical and agricultural relevance, like the identification of the genomic changes that underpinned the evolution of blood-feeding parasitic ticks from ancestors that weren’t blood-feeders.»

The findings are published in Nature Communications.

Source: University of Bristol [May 24, 2019]



Scientists discover ancient seawater preserved from the last Ice Age

Twenty thousand years ago, in the thick of an Ice Age, Earth looked very different. Because water was locked up in glaciers hundreds of feet thick, which stretched down over Chicago and New York City, the ocean was smaller—shorelines extended hundreds of miles farther out, and the remaining water was saltier and colder.

Scientists discover ancient seawater preserved from the last Ice Age
Assistant Professor Clara Blattler with a vial of seawater dating to the last Ice Age
— about 20,000 years ago [Credit: Jean Lachat]

A University of Chicago scientist led a study that recently announced the discovery of the first-ever direct remnants of that ocean: pockets of seawater dating to the Ice Age, tucked inside rock formations in the middle of the Indian Ocean.

«Previously, all we had to go on to reconstruct seawater from the last Ice Age were indirect clues, like fossil corals and chemical signatures from sediments on the seafloor,» said Clara Blättler, an assistant professor of geophysical sciences at the University of Chicago, who studies Earth history using isotope geochemistry. «But from all indications, it looks pretty clear we now have an actual piece of this 20,000-year-old ocean.»

Blättler and the team made the discovery on a months-long scientific mission exploring the limestone deposits that form the Maldives, a set of tiny islands in the middle of the Indian Ocean. The ship, the JOIDES Resolution, is specifically built for ocean science and is equipped with a drill that can extract cores of rock over a mile long from up to three miles beneath the seafloor. Then scientists either vacuum out the water or use a hydraulic press to squeeze the water out of the sediments.

The scientists were actually studying those rocks to determine how sediments are formed in the area, which is influenced by the yearly Asian monsoon cycle. But when they extracted the water, they noticed their preliminary tests were coming back salty—much saltier than normal seawater. «That was the first indication we had something unusual on our hands,» Blättler said.

Scientists discover ancient seawater preserved from the last Ice Age
Scientists carry a core of rock extracted by drill
[Credit: Clara Blattler]

The scientists took the vials of water back to their labs and ran a rigorous battery of tests on the chemical elements and isotopes that made up the seawater. All of their data pointed to the same thing: The water was not from today’s ocean, but the last remnants of a previous era that had migrated slowly through the rock.

Scientists are interested in reconstructing the last Ice Age because the patterns that drove its circulation, climate and weather were very different from today’s—and understanding these patterns could shed light on how the planet’s climate will react in the future. «Any model you build of the climate has to be able to accurately predict the past,» Blättler said.

For example, she said, ocean circulation is a primary player in climate, and scientists have a lot of questions about how that looked during an Ice Age. «Since so much fresh water was pulled into glaciers, the oceans would have been significantly saltier—which is what we saw,» Blättler said. «The properties of the seawater we found in the Maldives suggests that salinity in the Southern Ocean may have been more important in driving circulation than it is today.

«It’s kind of a nice connection,» she said, «since Cesare Emiliani, who is widely regarded as the father of paleoceanography—reconstructing the ancient ocean—actually wrote his seminal paper on the subject here at the University of Chicago in 1955.»

Their readings from the water align with predictions based on other evidence—a nice confirmation, Blättler said. The findings may also suggest places to search for other such pockets of ancient water.

The findings are published in Geochimica et Cosmochimica Acta.

Author: Louise Lerner | Source: University of Chicago [May 24, 2019]



2019 May 27 A Volcano of Fire under a Milky Way of Stars Image…

2019 May 27

A Volcano of Fire under a Milky Way of Stars
Image Credit & Copyright: Diego Rizzo

Explanation: Sometimes it’s hard to decide which is more impressive – the land or the sky. On the land of the featured image, for example, the Volcano of Fire (Volcán de Fuego) is seen erupting topped by red-hot, wind-blown ash and with streams of glowing lava running down its side. Lights from neighboring towns are seen through a thin haze below. In the sky, though, the central plane of our Milky Way Galaxy runs diagonally from the upper left, with a fleeting meteor just below, and the trail of a satellite to the upper right. The planet Jupiter also appears toward the upper left, with the bright star Antares just to its right. Much of the land and the sky were captured together in a single, well-timed, 25-second exposure taken in mid-April from the side of Fuego’s sister volcano Acatenango in Guatemala. The image of the meteor, though, was captured in a similar frame taken about 30 minutes earlier – when the volanic eruption was not as photogenic – and added later digitally.

∞ Source: apod.nasa.gov/apod/ap190527.html

Global temperature change attributable to external factors, confirms new study

Researchers at the University of Oxford have confirmed that human activity and other external factors are responsible for the rise in global temperature. While this has been the consensus of the scientific community for a long time, uncertainty remained around how natural ocean-cycles might be influencing global warming over the course of multiple decades. The answer we can now give is: very little to none.

Global temperature change attributable to external factors, confirms new study
Researchers have confirmed that human activity and other external factors are responsible
for the rise in global temperature [Credit: Shutterstock]

In a new study, published in the Journal of Climate, researchers at the Environmental Change Institute looked at observed ocean and land temperature data since 1850. Apart from human-induced factors such as greenhouse gas concentrations, other occurrences such as volcanic eruptions, solar activity and air pollution peaks were included in the analysis. The findings demonstrated that slow-acting ocean cycles do not explain the long-term changes in global temperature, which includes several decades of accelerated or slowed warming.

«We can now say with confidence that human factors like greenhouse gas emissions and particulate pollution, along with year-to-year changes brought on by natural phenomenon like volcanic eruptions or the El Niño, are sufficient to explain virtually all of the long-term changes in temperature,» says study lead author Dr Karsten Haustein. «The idea that oceans could have been driving the climate in a colder or warmer direction for multiple decades in the past, and therefore will do so in the future, is unlikely to be correct.»

The study showed that global warming that occurred during the ‘early warming’ period (1915 — 1945) was in fact caused by external factors as well. Formerly, it had been largely attributed to natural ocean temperature changes, which is why there has been uncertainty over how much of global warming is influenced by unpredictable natural factors.

«Our study showed that there are no hidden drivers of global mean temperature,» says co-author Dr Friederike Otto. «The temperature change we observe is due to the drivers we know. This sounds boring, but sometimes boring results are really important. In this case, it means we will not see any surprises when these drivers — such as gas emissions — change. In good news, this means when greenhouse gas concentrations go down, temperatures will do so as predicted; the bad news is there is nothing that saves us from temperatures going up as forecasted if we fail to drastically cut greenhouse gas emissions.»

Source: University of Oxford [May 22, 2019]



Researchers examine the age of groundwater in Egyptian aquifers

Most of the water used by people in Egypt comes from the Nile River, which originates from precipitation over mountainous areas in the Ethiopian highlands. In areas far from the Nile River Valley, however, where water is scarce and the population is growing, groundwater is the only available freshwater resource.

Researchers examine the age of groundwater in Egyptian aquifers
UD doctoral candidate Mahmoud Sherif takes groundwater samples from an aquifer in Egypt
[Credit: Mahmoud Sherif]

Knowing how much water is available in the groundwater aquifers and how fast it is being replenished is vital for providing the population with water for drinking and irrigation. Determining the age of water sources helps in those calculations.
A new study from the University of Delaware looked at chlorine isotopes as chemical tracers to determine the age and origin of groundwaters from the Eastern Desert of Egypt. The research was led by doctoral candidate Mahmoud Sherif and Neil Sturchio from UD and Mohamed Sultan from Western Michigan University. The work resulted in a paper recently published in the Earth and Planetary Science Letters journal.

While groundwater provides only seven percent of the water demand in Egypt, Egyptian water authorities have recently given renewed attention to increasing its exploitation, especially in eastern Egypt, to mitigate the growing water stress and to accommodate agriculture projects.

Researchers examine the age of groundwater in Egyptian aquifers
Neil Sturchio, professor and chair of the Department of Geological Sciences in UD’s College of Earth,
Ocean and Environment, said that the Egypt’s Eastern Desert is interesting because while it is
still dry and arid, it gets more rain than the Western Desert [Credit: Mahmoud Sherif]

To measure the age and origin of the groundwater, 29 samples were collected from different wells during several field expeditions in Egypt. The researchers used the long-lived radioactive isotope chlorine-36 to estimate the age of the groundwaters; this isotope forms in the atmosphere and travels to the earth and has a half-life of 300,000 years.
Sturchio, professor and chair of the Department of Geological Sciences in UD’s College of Earth, Ocean and Environment, said that the Eastern Desert is interesting because while it is still dry and arid, it gets more rain than the Western Desert of Egypt.

Because of this rain, the researchers were curious to see if the groundwater in the Eastern Desert might be generally younger than the water found in the Western Desert, but were surprised by their findings.

Researchers examine the age of groundwater in Egyptian aquifers
The Nile River provides most of the water used by Egyptians, but national authorities are looking
for ways increase the use of groundwater [Credit: Mahmoud Sherif]

«In the shallow aquifers you would expect young water, perhaps 50-100 years old, because it’s coming down as rain and flowing out towards the Nile Valley,» said Sturchio. «But in some of these aquifers, Mahmoud found water that’s apparently 200,000 years old.»
Sturchio said that while the water is probably not actually 200,000 years old, the fact that it appears that way shows that older water from the Nubian Aquifer comes up along faults in the rocks and mixes in with the shallow water, carrying some of the older chlorine with it.

The water coming up from the deeper aquifer likely ended up there when the climate was much wetter—as far back as a million years ago—with abundant rainfall that caused a lot of water to seep into the ground and collect in the very thick, porous sandstone.

Researchers examine the age of groundwater in Egyptian aquifers
Knowing how much water is available in the groundwater aquifers and how fast it is being replenished
is vital for providing the population with water for drinking and irrigation. Determining the age
of water sources helps in those calculations [Credit: Mahmoud Sherif]

Sherif said that finding this natural discharge from the deep aquifers through these faults to the shallower aquifers is important for the developmental plan for the area.
«When we quantify the amount of water in the shallow aquifer, we have to consider the water coming up from the deeper aquifer,» said Sherif. «It’s an additional source and instead of drilling very deep wells, which is very expensive, the [Egyptian government] won’t have to. They can reduce the cost.»

Sturchio said that while Egypt is lucky that it has a lot of water from the Nile, there is only so much water that can be taken out of the river according to an international agreement. That is why it is critical in areas like the Eastern Desert to identify and use these groundwater resources.

Researchers examine the age of groundwater in Egyptian aquifers
To measure the age and origin of the groundwater, 29 samples were collected from different wells during several field
expeditions in Egypt. The researchers used the long-lived radioactive isotope chlorine-36 to estimate the age of the
groundwaters; this isotope forms in the atmosphere and travels to the earth and has a half-life of 300,000 years
[Credit: Mahmoud Sherif]

«The young groundwater that comes down as rain and takes about 50 to 100 years to flow to the Nile is being used for irrigation in some places. But some of the water they’re pumping out comes from the much older groundwater in aquifer underneath,» said Sturchio. «You really want to know how much of that water you can pump out before you’re over-pumping it and using it up too fast. You don’t want to pump it out faster than it can replenish itself, ideally. Knowing the groundwater age is part of the basis for developing a good strategy for using it.»

Author: Adam Thomas | Source: University of Delaware [May 22, 2019]



Banded Fluorite Slab | #Geology #GeologyPage #Mineral Locality:…

Banded Fluorite Slab | #Geology #GeologyPage #Mineral

Locality: South Africa

Size : 17,7 x 12,2 x 1,5 cm

Photo Copyright © Le Comptoir Géologique

Geology Page



Aquamarine | #Geology #GeologyPage #Mineral Locality: Skardu…

Aquamarine | #Geology #GeologyPage #Mineral

Locality: Skardu District, Gilgit-Baltistan (Northern Areas), Pakistan

Size : 5,8 x 4,9 x 5,6 cm

Photo Copyright © Le Comptoir Géologique

Geology Page



Strange Martian mineral deposit likely sourced from volcanic explosions

Ashfall from ancient volcanic explosions is the likely source of a strange mineral deposit near the landing site for NASA’s next Mars rover, a new study finds. The research, published in the journal Geology, could help scientists assemble a timeline of volcanic activity and environmental conditions on early Mars.

Strange Martian mineral deposit likely sourced from volcanic explosions
New research shows that a strange Martian mineral deposit, imaged here from orbit,
was likely made by ashfall from ancient volcanic explosions
[Credit: NASA/Christopher Kremer/Brown University]

«This is one of the most tangible pieces of evidence yet for the idea that explosive volcanism was more common on early Mars,» said Christopher Kremer, a graduate student at Brown University who led the work. «Understanding how important explosive volcanism was on early Mars is ultimately important for understand the water budget in Martian magma, groundwater abundance and the thickness of the atmosphere.»

Volcanic explosions happen when gases like water vapor are dissolved in underground magma. When the pressure of that dissolved gas is more than the rock above can hold, it explodes, sending a fiery cloud of ash and lava into the air. Scientists think that these kinds of eruptions should have happened very early in Martian history, when there was more water available to get mixed with magma. As the planet dried out, the volcanic explosions would have died down and given way to more effusive volcanism — a gentler oozing of lava onto the surface. There’s plenty of evidence of an effusive phase to be found on the Martian surface, but evidence of the early explosive phase hasn’t been easy to spot with orbital instruments, Kremer says.

This new study looked at a deposit located in a region called Nili Fossae that’s long been of interest to scientists. The deposit is rich in the mineral olivine, which is common in planetary interiors. That suggests that the deposit is derived from deep underground, but it hasn’t been clear how the material got to the surface. Some researchers have suggested that it’s yet another example of an effusive lava flow. Others have suggested that the material was dredged up by a large asteroid impact — the impact that formed the giant Isidis Basin in which the deposit sits.

For this study, Kremer and colleagues from Brown used high-resolution images from NASA’s Mars Reconnaissance Orbiter to look at the geology of the deposit in fine detail. Kremer’s co-authors on the work are fellow Brown graduate student Mike Bramble, and Jack Mustard, a professor in Brown’s Department of Earth, Environmental and Planetary Sciences and Kremer’s advisor.

«This work departed methodologically from what other folks have done by looking at the physical shape of the terrains that are composed of this bedrock,» Kremer said. «What’s the geometry, the thickness and orientation of the layers that make it up. We found that the explosive volcanism and ashfall explanation ticks all the right boxes, while all of the alternative ideas for what this deposit might be disagree in several important respects with what we observe from orbit.»

Strange Martian mineral deposit likely sourced from volcanic explosions
The Mars 2020 rover is headed for Jezero crater. In addition to a stunning river delta, Jezero also has exposures
of the potential ashfall deposit that was the focus of this study. The rover could confirm these new findings,
which will be one of the rover’s «top 10 discoveries,» says Brown professor Jack Mustard
[Credit: NASA]

The work showed the deposit extends across the surface evenly in long continuous layers that drape evenly across hills, valleys, craters and other features. That even distribution, Kremer says, is much more consistent with ashfall than lava flow. A lava flow would be expected to pool in low-lying areas and leave thin or non-existent traces in highlands.

And the stratigraphic relationships in the area rule out an origin associated with the Isidis impact, the researchers say. They showed that the deposit sits on top of features that are known to have come after the Isidis event, suggesting that the deposit itself came after as well.

The ashfall explanation also helps to account for the deposit’s unusual mineral signatures, the researchers say. The olivine shows signs of widespread alteration through contact with water — far more alteration than other olivine deposits on Mars. That makes sense if this were ashfall, which is porous and therefore susceptible to alteration by small amounts of water, the researchers say.

All told, the researchers say, these orbital data strongly lean toward an ashfall origin. But the team won’t have to rely only on orbital data for long. NASA’s Mars2020 rover is scheduled to land in Jezero Crater, which sits within the olivine deposit. And there are exposures of the deposit within the crater. The olivine-rich unit will almost certainly be one of the rover’s exploration targets, and it might have the final say on what this deposit is.

«What’s exciting is that we’ll see very soon if I’m right or wrong,» Kremer said. «So that’s a little nerve wracking, but if it’s not an ashfall, it’s probably going to be something much stranger. That’s just as fun if not more so.»

If it does turn out to be ashfall, Kremer says, it validates the methodology used in this study as a means of looking at potential ashfall deposits elsewhere on Mars.

But whatever the rover finds will be important in understanding the evolution of the Red Planet.

«One of Mars 2020’s top 10 discoveries is going to be figuring out what this olivine-bearing unit is,» said Mustard, Kremer’s advisor. «That’s something people will be writing and talking about for a long time.»

Source: Brown University [May 22, 2019]




    Солнечное затмение 14 декабря 2020 года  — полное  солнечное затмение  142  сароса , которое лучше всего будет видно в юго-восточной час...