|Iron meteorites. By Waifer X (originally posted to Flickr as 090423-1080887) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons|
Tuesday, 23 February 2016
New research suggests there could be a layer of iron-rich meteorites hidden just under the Antarctic ice.
The churning of glaciers spews many space rocks out on to the surface in Antarctica, but compared to elsewhere on Earth, few of them are made of iron.
Based on modelling and lab experiments, scientists say the missing metallic rocks might be burying themselves, by melting the ice as sunlight heats them.
To prove their idea, the team now wants to look for the rocks themselves.
"The study is proposing a hypothesis - these samples should be there. We just have to go and locate them," said Dr Katherine Joy from the University of Manchester, a co-author of the paper published in Nature Communications.
Antarctica is known by meteorite specialists as a fruitful hunting ground, because the rocks are collected from their landing sites by glacial flows and transported to concentrated dumping-grounds.
"The great thing about Antarctica is they fall on the ice, and then the ice progressively moves away from the plateau. And where it hits these barriers, along the Transantarctic Mountains, the ice gets moved up," Dr Joy told the BBC.
"So this continuous conveyor belt has delivered meteorites from the interior fall sites to the 'meteorite stranding zones' for the past couple of million years or so."
Among this Antarctic haul, however, researchers have noticed that iron-rich meteorites - whether partly or wholly made of the metal - are surprisingly scarce, compared to the percentage collected in other places around the world.
Dr Joy and her colleagues think they may have discovered why.
They froze two small meteorites of similar size and shape, one made of iron and the other rocky and non-metallic, inside blocks of ice. A special lamp was trained on the ice from above, to mimic the rays of the Sun.
Both meteorites, on repeated trials, melted their way downward through the ice block. But because the metal conducts heat more efficiently, the iron meteorite sank further, faster.
The researchers then expanded that observation using a mathematical simulation. Their model showed that this Sun-driven burrowing would be enough to cause iron-rich rocks to sink so much during the long summer days that, over the course of the year, it would account fairly precisely for the lack of iron space rocks welling their way to the surface of the Antarctic "stranding zones".
"The idea is, they never make it to the surface. They're forever trapped, 50-100cm or so below the ice," Dr Joy explained.
That means, if the team's findings are to be believed, that the hunt is on.
As Dr Joy's Manchester colleague Geoffrey Evatt put it: "The challenge is now set - to be the first team to locate this reserve of meteorites and retrieve samples from it."
Of all the meteorites gathered from Antarctica, only a handful - so far - have been pulled out from beneath the ice. This is mostly for practical reasons, Dr Joy said.
"When it's very cold... picking up the sample in a controlled way is difficult enough with things sitting on the surface. To access ones that are subsurface - nobody's really tried to do that so far."
So it will not be easy, but the team hopes that radar and metal detectors might help target the search. And the potential rewards are high.
"Every meteorite we find tells us something new about the Solar System," Dr Joy said.
Some are carbon-rich or rocky remnants from long before any planet clumped together; others - like iron and rocky-iron meteorites - offer clues from a more intermediate stage, when baby planets with cores, mantles and crusts were trying to form.
"The iron group represents meteorites that were once the cores and the internal structures of different planetesimals.
"We think there were probably hundreds of these early planets, that formed in the solar system but never really got big enough and were broken up in collision events."
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Monday, 15 February 2016
At the rate humans are emitting carbon into the atmosphere, Earth may suffer irreparable damage that could last tens of thousands of years, according to a new analysis published this week.
|Rising sea levels will threaten residents of many countries, say researchers.|
"Much of the carbon we are putting in the air from burning fossil fuels will stay there for thousands of years - and some of it will be there for more than 100,000 years," said Peter Clark, an Oregon State University paleoclimatologist and lead author on the article. "People need to understand that the effects of climate change on the planet won't go away, at least not for thousands of generations."
The researchers' analysis is being published this week in the journal Nature Climate Change.
Thomas Stocker of the University of Bern in Switzerland, who is past-co-chair of the IPCC's Working Group I, said the focus on climate change at the end of the 21st century needs to be shifted toward a much longer-term perspective.
"Our greenhouse gas emissions today produce climate-change commitments for many centuries to millennia," said Stocker, a climate modeler and co-author on the Nature Climate Change article. "It is high time that this essential irreversibility is placed into the focus of policy-makers.
"The long-term view sends the chilling message (about) what the real risks and consequences are of the fossil fuel era," Stocker added. "It will commit us to massive adaptation efforts so that for many, dislocation and migration becomes the only option."
Sea level rise is one of the most compelling impacts of global warming, yet its effects are just starting to be seen. The latest IPCC report, for example, calls for sea level rise of just one meter by the year 2100. In their analysis, however, the authors look at four difference sea level-rise scenarios based on different rates of warming, from a low end that could only be reached with massive efforts to eliminate fossil fuel use over the next few decades, to a higher rate based on the consumption of half the remaining fossil fuels over the next few centuries.
With just two degrees (Celsius) warming in the low-end scenario, sea levels are predicted to eventually rise by about 25 meters. With seven degrees warming at the high-end scenario, the rise is estimated at 50 meters, although over a period of several centuries to millennia.
"It takes sea level rise a very long time to react - on the order of centuries," Clark said. "It's like heating a pot of water on the stove; it doesn't boil for quite a while after the heat is turned on - but then it will continue to boil as long as the heat persists. Once carbon is in the atmosphere, it will stay there for tens or hundreds of thousands of years, and the warming, as well as the higher seas, will remain."
Clark said for the low-end scenario, an estimated 122 countries have at least 10 percent of their population in areas that will be directly affected by rising sea levels, and that some 1.3 billion - or 20 percent of the global population - live on lands that may be directly affected. The impacts become greater as the warming and sea level rise increases.
"We can't keep building seawalls that are 25 meters high," noted Clark, a professor in OSU's College of Earth, Ocean, and Atmospheric Sciences. "Entire populations of cities will eventually have to move."
Daniel Schrag, the Sturgis Hooper Professor of Geology at Harvard University, said there are moral questions about "what kind of environment we are passing along to future generations."
"Sea level rise may not seem like such a big deal today, but we are making choices that will affect our grandchildren's grandchildren - and beyond," said Schrag, a co-author on the analysis and director of Harvard's Center for the Environment. "We need to think carefully about the long time-scales of what we are unleashing."
The new paper makes the fundamental point that considering the long time scales of the carbon cycle and of climate change means that reducing emissions slightly or even significantly is not sufficient. "To spare future generations from the worst impacts of climate change, the target must be zero - or even negative carbon emissions - as soon as possible," Clark said.
"Taking the first steps is important, but it is essential to see these as the start of a path toward total decarbonization," Schrag pointed out. "This means continuing to invest in innovation that can someday replace fossil fuels altogether. Partial reductions are not going to do the job."
Stocker said that in the last 50 years alone, humans have changed the climate on a global scale, initiating the Anthropocene, a new geological era with fundamentally altered living conditions for the next many thousands of years.
"Because we do not know to what extent adaptation will be possible for humans and ecosystems, all our efforts must focus on a rapid and complete decarbonization -the only option to limit climate change," Stocker said.
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Tuesday, 9 February 2016
In 1996, only a little more than a year after they created element 111, a team of German scientists led by Peter Armbruster at the Gesellschaft für schwerionenforschung (GSI) facility at Darmstadt, Germany, claimed to have created an atom of the element 112. Its nucleus has 112 protons and 166 neutrons, giving it a mass number of 277. As a new element it was named ununbium, symbol Uub, according to an internationally adopted system for naming new elements. This was based on the presence of one atom of the element made by accelerating zinc atoms to high speed and bombarding them into lead. When an atom of each fused to make the new nucleus, it lasted a fraction of a thousandth of a second before decaying, emitting an alpha particle to become a nucleus of element 110.
What is an element?
A chemical element or element is a species of atoms having the same number of protons in their atomic nuclei (i.e. the same atomic number, Z). There are 118 elements that have been identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radioactive isotopes, which decay over time into other elements. Iron is the most abundant element (by mass) making up the Earth, while oxygen is the most common element in the crust of the earth.
|The Periodic Table, by Sandbh (Own work) via Wikimedia Commons|
Chemical elements constitute all of the ordinary matter of the universe. However astronomical observations suggest that ordinary observable matter is only approximately 15% of the matter in the universe: the remainder is dark matter, the composition of which is unknown, but it is not composed of chemical elements. The two lightest elements, hydrogen and helium were mostly formed in the Big Bang and are the most common elements in the universe. The next three elements (lithium, beryllium and boron) were formed mostly by cosmic ray spallation, and are thus more rare than those that follow. Formation of elements with from six to twenty six protons occurred and continues to occur in main sequence stars via stellar nucleosynthesis. The high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars. Elements with greater than twenty-six protons are formed by supernova nucleosynthesis in supernovae, which, when they explode, blast these elements far into space as planetary nebulae, where they may become incorporated into planets when they are formed.
The term "element" is used for a kind of atom with a given number of protons (regardless of whether they are or they are not ionized or chemically bonded, e.g. hydrogen in water) as well as for a pure chemical substance consisting of a single element (e.g. hydrogen gas).
When different elements are chemically combined, with the atoms held together by chemical bonds, they form chemical compounds. Only a minority of elements are found uncombined as relatively pure minerals. Among the more common of such "native elements" are copper, silver, gold, carbon (as coal, graphite, or diamonds), and sulphur. All but a few of the most inert elements, such as noble gases and noble metals, are usually found on Earth in chemically combined form, as chemical compounds. While about 32 of the chemical elements occur on Earth in native uncombined forms, most of these occur as mixtures. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, and native solid elements occur in alloys, such as that of iron and nickel.
The history of the discovery and use of the elements began with primitive human societies that found native elements like carbon, sulphur, copper and gold. Later civilizations extracted elemental copper, tin, lead and iron from their ores by smelting, using charcoal. Alchemists and chemists subsequently identified many more, with almost all of the naturally-occurring elements becoming known by 1900.
The properties of the chemical elements are summarized on the periodic table, which organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. Save for unstable radioactive elements with short half-lives, all of the elements are available industrially, most of them in high degrees of purity.
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Wednesday, 3 February 2016
The moon was formed by a violent, head-on collision between the early Earth and a "planetary embryo" called Theia approximately 100 million years after the Earth formed, UCLA geochemists and colleagues report.
Scientists had already known about this high-speed crash, which occurred almost 4.5 billion years ago, but many thought the Earth collided with Theia (pronounced THAY-eh) at an angle of 45 degrees or more -- a powerful side-swipe (simulated in this 2012 YouTube video). New evidence reported Jan. 29 in the journal Science substantially strengthens the case for a head-on assault.
The researchers analyzed seven rocks brought to the Earth from the moon by the Apollo 12, 15 and 17 missions, as well as six volcanic rocks from the Earth's mantle - five from Hawaii and one from Arizona.
|By Gregory H. Revera (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons|
The key to reconstructing the giant impact was a chemical signature revealed in the rocks' oxygen atoms. (Oxygen makes up 90 percent of rocks' volume and 50 percent of their weight.) More than 99.9 percent of Earth's oxygen is O-16, so called because each atom contains eight protons and eight neutrons. But there also are small quantities of heavier oxygen isotopes: O-17, which have one extra neutron, and O-18, which have two extra neutrons. Earth, Mars and other planetary bodies in our solar system each has a unique ratio of O-17 to O-16 - each one a distinctive "fingerprint."
In 2014, a team of German scientists reported in Science that the moon also has its own unique ratio of oxygen isotopes, different from Earth's. The new research finds that is not the case.
"We don't see any difference between the Earth's and the moon's oxygen isotopes; they're indistinguishable," said Edward Young, lead author of the new study and a UCLA professor of geochemistry and cosmochemistry.
Young's research team used state-of-the-art technology and techniques to make extraordinarily precise and careful measurements, and verified them with UCLA's new mass spectrometer.
The fact that oxygen in rocks on the Earth and our moon share chemical signatures was very telling, Young said. Had Earth and Theia collided in a glancing side blow, the vast majority of the moon would have been made mainly of Theia, and the Earth and moon should have different oxygen isotopes. A head-on collision, however, likely would have resulted in similar chemical composition of both Earth and the moon.
"Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them," Young said. "This explains why we don't see a different signature of Theia in the moon versus the Earth."
Theia, which did not survive the collision (except that it now makes up large parts of Earth and the moon) was growing and probably would have become a planet if the crash had not occurred, Young said. Young and some other scientists believe the planet was approximately the same size as the Earth; others believe it was smaller, perhaps more similar in size to Mars.
Another interesting question is whether the collision with Theia removed any water that the early Earth may have contained. After the collision - perhaps tens of millions of year later - small asteroids likely hit the Earth, including ones that may have been rich in water, Young said. Collisions of growing bodies occurred very frequently back then, he said, although Mars avoided large collisions.
A head-on collision was initially proposed in 2012 by Matija, now a research scientist with the SETI Institute, and Sarah Stewart, now a professor at UC Davis; and, separately during the same year by Robin Canup of the Southwest Research Institute.
Co-authors of the Science paper are Issaku Kohl, a researcher in Young's laboratory; Paul Warren, a researcher in the UCLA department of Earth, planetary, and space sciences; David Rubie, a research professor at Germany's Bayerisches Geoinstitut, University of Bayreuth; and Seth Jacobson and Alessandro Morbidelli, planetary scientists at France's Laboratoire Lagrange, Université de Nice.
The research was funded by NASA, the Deep Carbon Observatory and a European Research Council advanced grant (ACCRETE).
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