Tagged: COSMOS Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 12:39 pm on June 23, 2018 Permalink | Reply
    Tags: "Stop looking for ET: modelling suggests we’re alone in the universe", COSMOS, , , Future of Humanity Institute,   

    From Future of Humanity Institute at University of Oxford via COSMOS: “Stop looking for ET: modelling suggests we’re alone in the universe” 

    U Oxford bloc

    From University of Oxford

    1

    Future of Humanity Institute

    COSMOS

    20 June 2018
    Andrew Masterson

    2
    Contact, Jodi Foster. No image credit found

    Despite the small matter of lack of evidence, most astrophysicists and cosmologists today are persuaded that extra-terrestrial intelligent life must exist.

    The logic behind the assumption seems compelling. There are billions of galaxies in the universe, each containing billions of stars, around a proportion of which orbit billions of planets. Given the vastness of those numbers, it would be statistically perverse to suggest that intelligent life evolved only once in the entire system.

    But what, however, if the startlingly improbable is nevertheless the truth? What if Homo sapiens is, in fact, the only species ever in the entire history of the universe to invent radio, build an X-ray observatory, and send a ship into space?

    What if – the existence of exoplanets coated in blue-green slime notwithstanding – we are utterly on our own?

    That’s the contention of physicists Anders Sandberg, Eric Drexler and Toby Ord, all of the Future of Humanity Institute at Oxford University in the UK. In a paper lodged on the pre-print server Arxiv, and thus still awaiting peer review, the trio model what happens when two touchstones of astrobiology – the Fermi Paradox and the Drake Equation – are combined and subjected to mathematical rigour.

    2
    The Fermi Paradox, named for Dr. Enrico Fermi, describes the apparent contradiction between the lack of evidence of extraterrestrial civilizations and the high probability that such alien life exists. AP

    Frank Drake, SET Institute. No image credit

    Drake Equation, Frank Drake, Seti Institute

    The results, it must be said, aren’t good, at least for people hopeful that somewhere, out there, at least one alien civilisation is bubbling along.

    Existing calculations for the probability of extra-terrestrial intelligent life, they report, rest on uncertainties and assumptions that lead to outcomes containing margins for error spanning “multiple orders of magnitude”.

    Constraining these, as much as possible, by factoring in models of plausible chemical and genetic mechanisms, results, they conclude, in the finding “that there is a substantial probability that we are alone”.

    The Fermi Paradox is named after physicist Enrico Fermi, who noted in 1950 that there are so many stars, just in the Milky Way, that given the age of the universe even a small probability that intelligent life has evolved would mean that their existence should be plain to humanity by now.

    Yet, he continued, in terms of evidence, we have squat, which, given the probability of intelligent life emerging, is odd. Hence the paradox. “Where are they?” he asked.

    The Drake Equation, formulated by American astronomer Frank Drake in 1961, attempts to place an analytical framework around Fermi’s contention, by estimating the number of intelligent civilisations that exist in the universe, regardless of the fact that we can’t see them.

    In the equation, N represents the number of civilisations within the Milky Way capable of emitting detectable electromagnetic signals. The number is determined by the other factors in the model, which express the rate of suitable star formation, the fraction of those stars with exoplanets, the number of those planets suitable for life and the number on which life actually appears.

    That total is then further reduced by adding in other refinements – the number of life-bearing planets on which intelligence emerges, the number of those that produce technology capable of emitting signals into space, and the number of those that actually go ahead and do so.

    It’s all very impressive, but “sciencey” rather than scientific. Sandberg, Drexler and Ord gleefully quote US astronomer Jill Tarter, who described the Drake Equation as “a wonderful way to organise our ignorance”.

    The problem with the way the equation is usually wielded, the researchers argue, is that the parameters assigned to most of the various elements represent simply best guesses – and those guesses, furthermore, are heavily influenced by whether the person making them is optimistic or pessimistic about the chances of intelligent life existing. The result, they note, often involves well-estimated astronomical numbers multiplied by ad hoc figures.

    They quote another US astronomer, Steven J. Dick: “Perhaps never in the history of science has an equation been devised yielding values differing by eight orders of magnitude … each scientist seems to bring his own prejudices and assumptions to the problem.”

    Dick, they note, was being nice. Many outcomes from Drake Equation calculations yield probabilities that range over hundreds of orders of magnitude.

    In a not altogether unrelated sidebar, the researchers acknowledge a recent calculation by Swedish-American cosmologist Max Tegmark, estimating the chances of intelligent civilisations arising in the universe.

    Tegmark assumes there is no reason two intelligent civilisations should be any particular distance from each other, and then argues that – given the Milky Way is a minuscule fraction of the observable universe, which is itself only a tiny part of the universe beyond what we can see – it is unlikely that two intelligent civilisations would arise in the same observable universe. Thus, to all intents and purposes, we are very probably alone.

    Sandberg, Drexler and Ord use a different approach in their modelling, incorporating current scientific uncertainties that produce values for different parts of the equation ranging over tens and hundreds of orders of magnitude. Some of these concern critical questions regarding the emergence of life from non-living material – a process known as abiogenesis – and the subsequent likelihoods of early RNA-like life evolving into more adaptive DNA-like life.

    Then there is the essential matter of that primitive DNA-like life undergoing the sort of evolutionary symbiotic development that occurred on Earth, when a relationship between two different types of simple organisms resulted in the complex “eukaryotic” cells that constitute every species on the planet more complicated than bacteria.

    The results are depressing enough to send a thousand science-fiction writers into catatonic shock. The Fermi Paradox, they find, dissolves.

    “When we take account of realistic uncertainty, replacing point estimates by probability distributions that reflect current scientific understanding, we find no reason to be highly confident that the galaxy (or observable universe) contains other civilizations,” they conclude.

    “When we update this prior in light of the Fermi observation, we find a substantial probability that we are alone in our galaxy, and perhaps even in our observable universe.

    “‘Where are they?’ — probably extremely far away, and quite possibly beyond the cosmological horizon and forever unreachable.”

    See the full article here.


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Oxford campus

    Oxford is a collegiate university, consisting of the central University and colleges. The central University is composed of academic departments and research centres, administrative departments, libraries and museums. The 38 colleges are self-governing and financially independent institutions, which are related to the central University in a federal system. There are also six permanent private halls, which were founded by different Christian denominations and which still retain their Christian character.

    The different roles of the colleges and the University have evolved over time.

    Advertisements
     
  • richardmitnick 9:26 am on April 18, 2018 Permalink | Reply
    Tags: 'Nuclear geyser' may be origin of life, , , COSMOS, , ,   

    From Tokyo Institute of Technology via COSMOS: “‘Nuclear geyser’ may be origin of life” 

    tokyo-tech-bloc

    Tokyo Institute of Technology

    COSMOS

    18 April 2018
    Richard A. Lovett

    1
    A natural geyser hearing by nuclear fission in a uranium deposit may have provided the ideal conditions for biomolecules to form. SOPA Images / Getty.

    Life may not have originated in the primordial soup of an ancient pond, according to scientists, but rather in a “nuclear geyser” powered by an ancient uranium deposit.

    Shigenori Maruyama of Tokyo Institute of Technology says the idea came from what chemists know about crucial compounds in our own bodies.

    Many of these compounds – including DNA and proteins – are polymers formed from chains of smaller building blocks.

    Each of these molecules serves a different purpose in the body, but something they all have in common, says Nicholas Hud, a chemist from Georgia Institute of Technology, Atlanta, is that a molecule of water is released when each new building block is added.

    “There is a theme here,” he said last week at a NASA-sponsored symposium on the early solar system and the origins of life. To a chemist, this suggests that these biopolymers must have originated under relatively dry conditions.

    Otherwise, Hud says, the presence of water would have forced the reactions to run backwards, breaking chains apart. But, there’s a problem: most scientists assume life started in water.

    The solution to this paradox, according to Hud, comes from realizing that water comes and goes. The major chemicals of life, and presumably life itself, may have formed in an environment that was alternately wet and dry. “It could be seasonal,” he says. “It could be tides. It could be aerosols that go up [into the air] and come back down.”

    Some prebiotic chemical reactions occur easily at moderate temperatures, but others, says Robert Pascal, a physical organic chemist from the University of Montpellier, France, require a more concentrated source of energy. This energy may have come from the sun, which in the early solar system was considerably more active than today. But another source is radiation.

    Which brings us back to nuclear geysers.

    Based on analyses similar to Hud’s and Pascal’s, Maruyama has identified nine requirements for the birthplace of life. One place where all can occur at once, Maruyama says, is in the plumbing of a nuclear geyser [Geoscience Frontiers].

    This would not only produce heat to power the geyser, but produce radiation strong enough to break the recalcitrant molecular bonds of water, nitrogen, and carbon dioxide, all of which must be cleaved in order to produce critical prebiotic compounds. Periodic eruptions of the geyser would also produce alternating wet and dry cycles, and water draining from the surface would bring back dissolved gases from the atmosphere. The rocks lining the geyser’s subterranean channels would provide a source of minerals such as potassium and calcium.

    “This is the place I recommend [for the origin of life],” Maruyama says.

    Once life originated, he says, it would have been spewed onto the surface and from there into the oceans. From there, it spread to every known habitable niche on the modern Earth.

    Extraterrestrial life (or at least life as we know it), he says, would need similar conditions in which to originate.

    That, he thinks, means the best place to look for it in our solar system is Mars. However habitable the subsurface oceans of outer moons such as Ganymede, Europa, and Titan may be for bacteria, they likely lack the conditions needed for the origin of life as we know it, he says.

    As for exoplanets? Similar conditions are also needed there, he says, including not only an energy source to power pre-biotic reactions, but a “triple junction” between rock, air, and water, where all the needed materials can come together simultaneously.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    tokyo-tech-campus

    Tokyo Tech is the top national university for science and technology in Japan with a history spanning more than 130 years. Of the approximately 10,000 students at the Ookayama, Suzukakedai, and Tamachi Campuses, half are in their bachelor’s degree program while the other half are in master’s and doctoral degree programs. International students number 1,200. There are 1,200 faculty and 600 administrative and technical staff members.

    In the 21st century, the role of science and technology universities has become increasingly important. Tokyo Tech continues to develop global leaders in the fields of science and technology, and contributes to the betterment of society through its research, focusing on solutions to global issues. The Institute’s long-term goal is to become the world’s leading science and technology university.

     
  • richardmitnick 5:29 am on March 14, 2018 Permalink | Reply
    Tags: , , , , COSMOS, The Harvard "Computers"   

    From COSMOS: Women in STEM-“Forgotten women in science: The Harvard Computers” 

    Cosmos Magazine bloc

    COSMOS Magazine

    14 March 2018
    Zing Tsjeng

    Part 1 of 3

    1
    The Harvard Computers. Sara Netherway.

    The era of human computers didn’t begin with the West Computers or the Bletchleyettes. Toward the end of the 19th century, Harvard College Observatory drafted in dozens of women to take on one of the most unique mathematical computing jobs in its 178-year history: to unravel the mysteries of the heavens by calculating the positions of the stars.

    The work was less glamorous than it sounded. Thanks to new photographic technology, astronomers were able to capture images of the night sky onto glass plates. The problem, however, was that there was far too much data and too few people to analyse it.

    Observatory director Edward Charles Pickering (1846–1919) had an unusual solution: he employed a team of women to do it.

    2
    Edward Charles Pickering (1846–1919), Wikipedia.

    At the time, bright and talented graduates were emerging from America’s newly founded women’s colleges – such as Vassar College in upstate New York – and on the hunt for employment prospects that offered a little more excitement than working as a schoolteacher or running a household. Being a computer was as good as it got, even if they were paid far less than their male colleagues at 25 to 30 cents an hour. But it wasn’t just middle-class educated women who were offered a chance at classifying the stars; there were also uneducated women like Williamina Fleming (1857–1911), a Dundee-born single mother and housemaid whose aptitude for computing led Pickering to promote her from cleaning his rooms to computing his plates.

    3
    Williamina Fleming (1857–1911), Wikipedia.

    The Harvard Computers (1881–1919) – or, as they more rudely began to be known at the time, Pickering’s Harem – worked in the library next to the observatory.

    4
    The Harvard Computers (1881–1919) [ Pickering’s Harem], Wikipedia.

    The process of measuring the brightness of the stars and their positions in the sky required painstaking attention to detail and utmost concentration. Though the work was considered boring and tedious – hence why women were landed with it – it was also a lot less straightforward than it seemed.

    Most plates simply revealed dark splodges of dots against the glass. With the careful application of mathematical formulae, the women could work out the coordinates of the stars and their brightness. The northern and southern skies had never been mapped in their entirety before. The Harvard College Observatory, with its immense collection of plates, stood the best chance of doing it, and it couldn’t have made any progress without its computers.

    4
    The Harvard College Observatory, Wikipedia.

    Then came another challenge: how should they categorise these celestial bodies? Wellesley College graduate Annie Jump Cannon (1863–1941) created the Harvard Classification Scheme, which sorts the stars based on qualities such as their colour and temperature.

    5
    Annie Jump Cannon (1863–1941), YouTube.

    As Cannon put it: “It was almost as if the distant stars had really acquired speech, and were able to tell of their constitution and physical condition.”

    Her system is still used by astronomers today.

    Cannon and another computer, Henrietta Swan Leavitt (1868–1921), were both deaf; in Cannon’s case, this proved advantageous when she wanted to concentrate at work, as she would simply remove her hearing aid to block out the noises of the outside world.

    6
    Henrietta Swan Leavitt (1868–1921), Wikepedia.

    Even though none of them – barring Cannon – were ever allowed to use the mighty Harvard telescope known as the Great Refractor, the computers were on the cutting edge of astronomical discovery.

    8
    The Harvard Great Refractor, https://www.pinterest.co.uk/pin/480266747745788652/

    Fleming, for instance, catalogued more than 10,000 stars and from earth. However, initial publications of the finding missed out her name completely. (Subsequent catalogues, thankfully, rectified the mistake.) In 1899 she became the Curator of astronomical photographs and was one of the few computers to be appointed to a professional position at Harvard.

    Leavitt, on the other hand, realised that some stars pulsate with consistent brightness, making these so-called Cepheid variables solid benchmarks for calculating distances across space: a method that Edwin Hubble relied on to prove that the universe goes beyond our own paltry galaxy. In this way, the findings made by the Harvard Computers were truly revolutionary.

    Edwin Hubble at Caltech Palomar Samuel Oschin 48 inch Telescope,(credit: Emilio Segre Visual Archives/AIP/SPL)

    Harvard continued to use photographic plates until the 1990s, when digital cameras supplanted the old way of doing things. But the 500,000 glass plates that the computers once pored over still reside at the university, along with 118 boxes of notes and logbooks recently unearthed by the curator of the Harvard-Smithsonian Centre for Astrophysics.

    Together, they constitute a perfect record of what the night sky looked like a century ago, and of the women who sat in the small room next to Harvard’s telescope, deciphering the secrets of the universe. In 2005 the Centre began cleaning and digitising each glass plate for its archive. At the time of writing, more than 207,000 images have been preserved.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 9:36 am on March 12, 2018 Permalink | Reply
    Tags: , , , , , Carbon-based molecules are a by-product of red giants, Circumstellar envelopes, , COSMOS, , Red Giant Stars, U Hawaii Manoa   

    From University of Hawaii Manoa via COSMOS: “Complex organic compounds from dying stars could be life precursors” 

    U Hawaii

    University of Hawaii Manoa

    COSMOS

    12 March 2018
    Richard A. Lovett

    Lab experiments reveal carbon-based molecules are a by-product of red giants.

    1
    A red giant star – the font, perhaps, of life… QAI Publishing/UIG via Getty Images

    Laboratory experiments designed to recreate conditions around carbon-rich red giant stars have revealed that startlingly complex organic compounds can form in the “circumstellar envelopes” created by stellar winds blowing off from them.

    The carbon is present because nuclear reactions in these dying stars have progressed to the point that much of their initial complement of hydrogen and helium has been converted into heavier elements such as carbon.

    “There is a lot of carbon in these circumstellar envelopes,” says Ralf Kaiser, a physical chemist at the University of Hawaii at Manoa, US.

    In research published in the journal Nature Astronomy, a team led by Kaiser used a high-temperature chemical reactor to simulate conditions inside these circumstellar envelopes.

    The goal, he says, is to demonstrate how complex compounds can be assembled a couple of carbon atoms at a time at temperatures of up to about 1200 degrees Celsius. Previous research found that a host of organic chemicals can indeed be formed, but the new study pushed the process farther, demonstrating that it is possible to create chemicals at least as complex as pyrene, a 16-carbon compound with a structure like four fused benzene rings.

    So far, pyrene is the most complex molecule constructed in this manner, but Kaiser thinks that it might be just the beginning. “We hope when we do further experiments that this can be extended,” he says.

    What this means, he explains, is that circumstellar envelopes might be able to create molecules with 60 or 70 carbons, or even nanoparticle-sized sheets of graphene, a material composed of a larger array of fused rings.

    Such materials, he says, can act as building blocks on which other molecules, such as water, methane, methanol, carbon monoxide, and ammonia can condense as they move away from the star and cool to temperatures as low as minu-263 degrees Celsius. When the resulting chemical stew is exposed to ionising radiation either from nearby sources or galactic cosmic rays, Kaiser says, they can form sugars, amino acids, and dipeptides.

    “These are molecules relevant to the origins of life,” he adds.

    Billions of years ago, such organic-rich particles may have found their way into asteroids that then rained down onto the primordial Earth, endowing us with the precursors for life.

    Pyrene is a member of a family of compounds called polycyclic aromatic hydrocarbons (PAHs), the simplest of which is naphthalene, the primary ingredient of mothballs. Simple PAHs have already been detected in space, but the holy grail, Kaiser says, will be if more complex ones, such as pyrene, are found by NASA’s OSIRIS-REx mission, now en route to asteroid 101955 Bennu, from which it is expected to send back a sample in 2023.

    NASA OSIRIS-REx Spacecraft

    “We do not know what this mission will find,” Kaiser says. But, “if they find carbonaceous materials such as PAHs, then our experiments say how this organic matter can be formed.”

    Humberto Campins, a planetary scientist from Central Florida University, Orlando, Florida, and member of the OSIRIS REx science team, agrees. Studying the chemical makeup of asteroids, he says, doesn’t just tell us about the composition of our own early solar system, but can also reveal information about “pre-solar” compounds.

    “One of the beauties of sample return missions is that the latest analytical techniques for chemical, mineralogical, and isotopic composition can be applied to very small components of the sample, such as pre-solar grains or molecules,” he says.

    “We know that the dust from these kinds of stars gets incorporated into meteorites, so they are absolutely contributing to the compounds that would be present within Bennu,” adds Chris Bennett, also of the University of Central Florida (and a former student of Kaiser’s, although he was not part of the present study team).

    Chris McKay, an astrobiologist at NASA Ames Research Centre in Moffett Field, California, adds that the paper supports the notion that that the universe contains a large amount of carbon in the form of organic molecules. “[That’s] not a new result,” he says, “but [it is] further support for this key idea in astrobiology.”

    Kaiser adds that the finding demonstrates the value of interdisciplinary studies.

    “Most of the scientists dealing with PAHs [in space] are astronomers,” he says. “They are excellent spectroscopists, but by nature, astronomy sometimes lacks fundamental knowledge about chemistry.”

    Laboratory studies are necessary to turn theories for how complex chemicals can form in space from “hand-waving” into something more definitive, he says.

    But the interdisciplinary impact goes beyond astronomy. Pyrene and other PAHs are common pollutants that can be incorporated into dangerous soot particles created by internal combustion engines and other industrial processes.

    Lessons from astrochemistry about how they can be formed, he says, says Kaiser, can therefore have the very practical side effect of helping us develop less-polluting automobile engines.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    System Overview

    The University of Hawai‘i System includes 10 campuses and dozens of educational, training and research centers across the Hawaiian Islands. As the public system of higher education in Hawai‘i, UH offers opportunities as unique and diverse as our Island home.

    The 10 UH campuses and educational centers on six Hawaiian Islands provide unique opportunities for both learning and recreation.

    UH is the State’s leading engine for economic growth and diversification, stimulating the local economy with jobs, research and skilled workers.

     
  • richardmitnick 9:16 am on January 15, 2018 Permalink | Reply
    Tags: , , , Citizen Science Exoplanet Explorers, , COSMOS, K2-138, Music of the spheres: chain of planets rotates at “perfect fifth” intervals, Zooniverse   

    From COSMOS Magazine: “Music of the spheres: chain of planets rotates at “perfect fifth” intervals” 

    Cosmos Magazine bloc

    COSMOS Magazine

    15 January 2018
    Richard A Lovett

    1
    In 1619 Johannes Kepler calculated the “divine” musical scales of the planets in the solar system. Now citizen science has found a strong musical equivalence in a chain of newly discovered exoplanets. Photo 12/UIG via Getty Images.

    With the help of citizen scientists, exoplanet hunters have made one of their most unusual discoveries yet: a system called K2-138 that contains five planets orbiting in near-perfect resonances so close to their star that all five orbits are less than 13 days.

    Orbital resonances occur when planetary orbits are spaced so that they circle their star in numerically related patterns. In the case of K2-138, this resonance is close to 3:2, which means that each planet makes three circuits of the star in the time it takes the next one out to make two. That is, the outer planet’s orbit is 50% longer than the inner one’s.

    1
    Artist’s concept of a top-down view of the K2-138 system discovered by citizen scientists, showing the orbits and relative sizes of the five known planets. Orbital periods of the five planets, shown to scale, fall close to a series of 3:2 mean motion resonances. This indicates that the planets orbiting K2-138, which likely formed much farther away from the star, migrated inward slowly and smoothly.
    Credit: NASA/JPL-Caltech/R. Hurt (IPAC)

    Such resonances are common in the planetary systems discovered by NASA’s Kepler space telescope (which seeks exoplanets by looking for dips in the brightness of distant stars that occur when planets cross in front of them, blocking part of their light). That’s because Kepler has discovered a great many compact planetary systems, in which planets would gravitationally interfere with each other if their orbits were not somehow synchronised.

    But K2-138 is the most dramatic example of this yet, with five planets — all between 1.6 and 3.3 times the size of the Earth — moving like clockwork in a succession of 3:2 resonances. Specifically, their orbits are 2.35, 3.56, 5.40, 8.26, and 12.76 days, forming an unbroken chain of close-to-3:2 resonances — the longest such chain ever discovered. Moreover, there are hints of a sixth planet, which, if it exists, would orbit in about 42 days.

    That’s particularly interesting, says Jessie Christiansen, an astronomer from California Institute of Technology, Pasadena, US, who presented her findings last week at a meeting of the American Astronomical Society in National Harbor, Maryland, because 42 days falls into the same resonance chain.

    That raises the possibility that there might be as-yet unobserved planets in the gaps between 12.76 days and 42. “If you continue the chain it would be 19, 27, and 42,” she says. “So it could be that the longest chain could get longer yet.”

    It’s an exciting discovery, says Steve Bryson, an exoplanet-hunting astronomer at NASA Ames Research Centre at Mountain View in California, who was not a member of Christiansen’s team. “It gives us a deeper understanding of how planetary systems form.”

    Christiansen agrees. The fact that the planets wound up in such a smooth arrangement, she says, suggests that they migrated inward to their present positions very sedately, rather than via chaotic gravitational interactions. “They had no fights,” she says.

    It’s also intriguing because the 3:2 interval between these planets’ orbits is what musicians call a perfect fifth. “You can find them everywhere in music,” Christiansen says, citing the first two notes of Twinkle, Twinkle, Little Star as an example.

    Even more interestingly, the orbits aren’t quite perfect fifths, but are just ever so slightly off, she says. That is, instead of having orbital resonances that are exactly in a 3:2 ratio (or 1.5 to 1), they are 1.513, 1.518, 1.528, and 1.544. That’s intriguing, she says, because musicians actually tune their instruments to be just slightly off from perfect-fifth intervals to avoid the irritating “beat” phenomena that happens when tuning is too perfect.

    Possibly, she says, K2-138’s planets may have wound up in orbits just slightly off from perfect in order to avoid being destabilised by a similar phenomena due to too-perfect synchronisation.

    But even more exciting than the science, says Bryson, is the way in which the find was made. It came via a project called Exoplanet Explorers carried out on a website called zooniverse.org.

    The goal of that project, says Christiansen, is to recruit volunteers to examine any data in which the computer found a blip that might be a planet.

    “They’re doing the vetting,” she says. “Looking through and saying, ‘This is junk; this is real.’

    “It’s really hard to tell the computer to find everything that looks like a blip, but not ‘that’ kind of blip or ‘that’ kind of blip or ‘that’ kind of blip. So we just tell the computer to find all the blips and we’ll check.”

    But with thousands of stars involved, and a desire to have at least 10 people look at everything that might be interesting, that involves a tremendous amount of person-power.

    “We just uploaded 55,000 new potential planetary signals,” Christiansen says. “We would never be able to get through all of the signals we have without our volunteers.”

    Meg Schwamb, an astronomer at the Gemini Observatory in Hilo, Hawaii, agrees.

    “In our Internet age, online citizen science is enabling scientists to enlist the help of the general public from around the globe to perform data sorting and analysis tasks that are impossible to automate, or would be insurmountable for a single person or small group to undertake,” she says.

    “With so many eyes looking at the data, these projects can find hidden gems that may have gone missed in today’s large datasets.”

    “One of the things I love about astronomy,” adds Bryson, “is that it’s the one science where everyone can relate to it. Everyone knows what it’s like to look up at the stars.”

    Caltech article is posted here:
    https://sciencesprings.wordpress.com/2018/01/12/from-caltech-citizen-scientists-discover-five-planet-system/

    Christiansen’s study is in the online edition of The Astronomical Journal.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 9:54 am on January 5, 2018 Permalink | Reply
    Tags: , Coral bleaching, COSMOS, , Widespread coral bleaching in Australia's Great Barrier Reef   

    From COSMOS Magazine: “Worldwide coral bleaching has sped up dramatically in 30 years” 

    Cosmos Magazine bloc

    COSMOS Magazine

    05 January 2018
    Tanya Loos

    International data predicts annual reef bleaching is a real possibility.

    1
    Bleaching events have sped up significantly since the 1980s. Reinhard Dirscherl/ullstein bild via Getty Images

    2
    Global Coral Bleaching. http://www.globalcoralbleaching.org .

    The time between coral bleaching events at multiple reef locations has decreased five-fold in the past four decades, new research has found.

    A study in the journal Science reports that time elapsed between bleaching events in the tropics has contracted from 25-to-30 years in the early 1980s to just six years by 2010.

    “Before the 1980s, mass bleaching of corals was unheard of, even during strong El Niño conditions, but now repeated bouts of regional-scale bleaching and mass mortality of corals have become the new normal around the world as temperatures continue to rise,” says lead author Terry Hughes of the ARC Centre of Excellence for Coral Reef Studies based at James Cook University in Queensland, Australia.

    Using data from 100 reef sites around the world, Hughes and colleagues from Australia, Saudi Arabia, Canada and the US demonstrate that tropical sea temperatures are warmer today during cooler-than-average La Niña conditions than they were 40 years ago during El Niño periods.

    They find that the frequency of the bleaching events is having dire consequences for the complex ecosystems of coral reefs, because six years is insufficient time for the mature assemblages of the reef to recover. Even the fastest growing coral communities take approximately 10 to 15 years to recover after a bleaching event.

    The researchers fear that annual bleaching could soon occur.

    “Reefs have entered a distinctive human-dominated era – the Anthropocene,” says co-author Mark Eakin of the US National Oceanic & Atmospheric Administration.

    “The climate has warmed rapidly in the past 50 years, first making El Niños dangerous for corals, and now we’re seeing the emergence of bleaching in every hot summer.”

    The timing and severity of mass bleaching events has varied across geographic regions. In the 1980s, the Western Atlantic and Pacific regions were at highest risk. More recently, bleaching risk has increased only slowly in the Western Atlantic, at an intermediate rate in the Pacific and very strongly in the Middle East and Australasian regions.

    The study highlights the Great Barrier Reef, which has bleached four times since 1998, including unprecedented back-to-back events in 2016 and 2017.

    3
    Widespread coral bleaching in Australia’s Great Barrier Reef. http://www.slate.com .

    The researchers conclude that the future conditions of reefs, and the ecosystem services they provide to people, will depend critically on the trajectory of global emissions.

    “We hope our stark results will help spur on the stronger action needed to reduce greenhouse gases in Australia, the United States and elsewhere,” says Hughes.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 9:29 am on January 5, 2018 Permalink | Reply
    Tags: , , , , , COSMOS, ,   

    From COSMOS: “Unlike Hollywood, the universe is full of big stars” 

    Cosmos Magazine bloc

    COSMOS Magazine

    05 January 2018
    Richard A Lovett

    Research finds massive star numbers have been underestimated – affecting calculations for black holes, neutron stars and gravitational waves.

    1
    This composite of 30 Doradus, aka the Tarantula Nebula, contains data from Chandra, Hubble, and Spitzer. Located in the Large Magellanic Cloud, the Tarantula Nebula is one of the largest star-forming regions close to the Milky Way. Universal History Archive / Contributor / Getty Images

    NASA/Chandra Telescope

    NASA/ESA Hubble Telescope

    NASA/Spitzer Infrared Telescope

    2
    Large Magellanic Cloud, NASA/ESA Hubble

    Giant stars hundreds of times more massive than the sun may have been much more common in the early universe than previously believed, astronomers say.

    The find, published in the journal Science, used the European Southern Observatory’s Very Large Telescope in Chile to examine about 800 stars in a “starburst” region called 30 Doradus (also known as the Tarantula Nebula) in the Large Magellanic Cloud, a galaxy about 160,000 light years away from the Milky Way.

    3
    30 Doradus, aka the Tarantula Nebula, ESO/VLT

    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    Using a spectrometer so sensitive it could pick out individual stars only 1.2 arcseconds apart (about 1/1500 the width of the full moon), the researchers counted substantially more high-mass stars – ranging from 30 to 200 times the mass of the sun – than predicted by long-standing models of star formation. Furthermore, the discrepancy was particularly large for the largest stars.

    Historically, astronomers have believed that the vast majority of stellar matter is in the form of myriad small stars, with only a fraction of it in giants of the type observed in 30 Doradus. (In fact, it was only recently that astronomers realized that the largest of these gigantic stars even existed.)

    But the new research appears to have stood the traditional notion on its head. “Our results suggest that a significant fraction [of the mass] is in high-mass stars,” says one of the authors, Chris Evans of the UK’s Astronomy Technology Centre, in Edinburgh, Scotland.

    That’s important, adds the study’s lead author, Fabian Schneider, an astrophysicist from the University of Oxford, because a star 100 times the mass of our sun isn’t equivalent to 100 suns.

    “These are extremely bright,” he says. “A 100 solar-mass star would be a million times brighter than our sun. You need only a handful of these to outshine all the others.”

    Such bright stars, he adds, are “cosmic engines” that blast out not only light but ionising radiation and strong stellar winds. They burn bright, but also die young in massive explosions that not only create black holes and neutron stars, but disperse the elements of planets — and life — into space: carbon, oxygen, silicon, iron, and many others.

    In the earliest universe, after it had cooled down from the initial fury of the Big Bang, there was nothing but hydrogen and helium, cold and dark, Schneider says. But about 150 million years later, astrophysicists believe that the infant universe’s “dark age” ended with the coalescing of these materials into the first stars and galaxies.

    The resulting burst of radiation not only brought light back to the universe, but produced a series of other important effects, including the production of ionising radiation, stellar winds, and supernovae. In combination, these shaped galaxies and slowed the rate of star formation enough to keep the first generation of stars from gobbling up all of the available matter.

    The result, Schneider says, was to “regulate” the star forming process “so that you [still] see stars forming today. Otherwise, it would have stopped early on.”

    In today’s universe, giant star-forming regions such as 30 Doradus are relatively rare. Ancient regions can still be studied by peering at distant galaxies, whose light has been traveling for billions of years, but these are far away and difficult to observe in detail.

    Having one nearby, where we can study it closely, is therefore a perfect opportunity, especially because 30 Doradus is so close and large that it is easily visible in a small telescope.

    And it is so bright that if it were in our own galaxy at the distance of the Orion Nebula’s star-forming cluster (easily visible to the naked eye) it would span an area 60 times larger than the full moon and cast visible shadows on cloudless nights, Schneider says.

    And while it doesn’t constitute a perfect laboratory – it has too many heavier elements, for example, to be a perfect analogy to star-forming regions in the earliest galaxies – the fact it contains so many super-massive stars has major ramifications for our understanding of our universe’s history.

    “There might [have been] 70% more supernovae, a tripling of the chemical yields and towards four times the ionising radiation from massive star populations,” says Schneider.

    “Also, the formation rate of black holes might be increased by 180%, directly translating into a corresponding increase of binary black hole mergers that have recently been detected via their gravitational wave signals.”

    Brad Tucker, an astrophysicist and cosmologist at Australian National University, calls the new study “a very good paper” with “wide-reaching impact.”

    Its authors, he adds comprise a “who’s who” of experts in the field.

    “[It] suggests we should expect more core-collapse supernovae, and thus more metals, in the early Universe,” he says. There should also be more black hole mergers to be detected in the future by the gravitational waves they produced.

    “Simply put,” he says, “more larger stars equals a more exciting universe.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 1:06 pm on January 2, 2018 Permalink | Reply
    Tags: , Artificial Intelligence (AI), BDI, Computers don’t have any common sense. They don’t know that a glass of water when dropped will fall- likely break- and surely wet the carpet, COSMOS, IBM's Watson which in 2011 beat human champions at the TV quiz Jeopardy can now diagnose pneumonia better than radiologists, Moravec’s paradox   

    From COSMOS: “Dark intentions: should we fear AI with purpose?” 

    Cosmos Magazine bloc

    COSMOS Magazine

    02 January 2018
    Toby Walsh

    1
    Will robots ever develop minds of their own? Only if we tell them to. GERARD JULIEN/AFP/Getty Images.

    It’s hard to ignore dystopian pronouncements about how Artificial Intelligence (AI) is going to take over our lives, especially when they come from luminaries in tech. Entrepreneur Elon Musk, for instance, says “If you’re not concerned about AI safety, you should be. Vastly more risk than North Korea.” And IT maven Erik Brnyojolfsson, at MIT, has quoted Vladimir Putin’s claim that “The one who be-comes leader in this sphere will be ruler of the world.”

    I understand the angst. AI is chalking up victories over human intelligence at an alarming rate. In 2016 AlphaGo, training itself on millions of human moves, beat the world Go champion, Lee Sedol. In 2017 the upgrade – AlphaGo Zero – trained itself to champion level in three days, without studying human moves.

    Watson, which in 2011 beat human champions at the TV quiz Jeopardy, can now diagnose pneumonia better than radiologists. And Kalashnikov are training neural networks to fire machine guns. What’s not to fear?

    3

    4

    The real danger would be AIs with bad intentions and the competence to act upon them outside their normally closed and narrow worlds. AI is a long way from having either.

    AlphaGo Zero isn’t going to wake up tomorrow, decide humans are no good at playing board games — not compared to AlphaZero, at least — and make some money beating us at online poker.

    And it’s certainly not going to wake up and decide to take over the world. That’s not in its code. It will never do anything but play the games we train it for. Indeed, it doesn’t even know it is playing board games. It will only ever do one thing: maxim-ise its estimate of the probability that it will win the current game. Other than that, it has no intentions of its own.

    However, some machines already exist that do have broader intentions. But don’t panic. Those intentions are very modest and still are played out in a closed world. For instance, punch a destination into the screen of an autonomous car and its in-tent is to get you from A to B. How it does that is up to the car.

    Deep Space 1, the first fully autonomous spacecraft, also has limited human-given goals. These include things like adjusting the trajectory to get a better look at a passing asteroid. The spacecraft works out precisely how to achieve such goals for itself.

    There’s even a now rather old branch of robot programming based on beliefs, desires & intentions that goes by the acronym BDI.

    In BDI, the robot has “beliefs” about the state of the world, some of which are programmed and others derived from its sensors. The robot might be given the “desire” of returning a book to the library. The robot’s “intentions” are the plan to execute this desire. So, based on its beliefs that the book is on my desk and my desk is in my office, the robot goes to my office, picks up the book, and drives it down the corridor to the library. We’ve been building robots that can achieve such simple goals now for decades.

    So, some machines already do have simple intentions. But there’s no reason to go sending out alarmed tweets. These intentions are always human-given and of rather limited extent.

    Am I being too complacent? Suppose for a moment we foolishly gave some evil intents to a machine. Perhaps robots were given the goal of invading some country. The first flight of stairs or closed door would likely defeat their evil plans.

    One of the more frustrating aspects of working on AI is that what seems hard is often easy and what seems easy is often hard. Playing chess, for instance, is hard for humans, but we can get machines to do it easily. On the other hand, picking up the chess pieces is child’s play for us but machines struggle. No robot has anything close to the dexterity of a three-year-old.

    This is known as Moravec’s paradox, after Carnegie Mellon University roboticist Hans Moravec. Steven Pinker has said that he considers Moravec’s paradox to be the main lesson uncovered by AI research in 35 years.

    I don’t entirely agree. I would hope that my colleagues and I have done more than just uncover Moravec’s paradox. Ask Siri a question. Or jump in a Tesla and press AutoPilot. Or get Amazon to recommend a book. These are all impressive exam-ples of AI in action today.

    But Moravec’s paradox does certainly highlight that we have a long way to go in getting machines to match, let alone exceed, our capabilities.

    Computers don’t have any common sense. They don’t know that a glass of water when dropped will fall, likely break, and surely wet the carpet. Computers don’t understand language with any real depth. Google Translate will finding nothing strange with translating “he was pregnant”. Computers are brittle and lack our adaptability to work on new problems. Computers have limited social and emotion-al intelligence. And computers certainly have no consciousness or sentience.

    One day, I expect, we will build computers that match humans. And, sometime after, computers that exceed humans. They’ll have intents. Just like our children (for they will be our children), we won’t want to spell out in painful detail all that they should do. We have, I predict, a century or so to ensure we give them good intents.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 11:20 am on December 27, 2017 Permalink | Reply
    Tags: COSMOS, , If there’s any consensus among geologists it is that something changed about 2.7 billion years ago to kick tectonic plates in action,   

    From COSMOS: “Plate tectonics: the hidden key to life on Earth” 

    Cosmos Magazine bloc

    COSMOS Magazine

    27 December 2017
    Richard A. Lovett

    Earth’s constantly moving crust helps keep the climate habitable. If circumstances had been only a little different, we could have ended up a barren hothouse like Venus or a frozen snowball like Mars. How did we get so lucky?

    1
    Vitalij Cerepok / Getty Images

    “Look again at that dot. That’s here. That’s home. That’s us.” Carl Sagan was moved to lyricism by the pale blue dot that Voyager 1 photographed as it exited the solar system 27 years ago. The pale blue dot is precious, and lucky.

    2
    Earth from Voyager 1

    NASA/Voyager 1

    Not only does Earth lie in the ‘Goldilocks zone’ that allows water to exist in the liquid form that life requires. It is also the only rocky planet we know of that constantly renovates its surface as its tectonic plates dive into the mantle in some places and re-emerge as molten lava in others.

    3
    The Earth’s rigid tectonic plates float on a playdoh-like mantle in slow, constant motion. Without this movement, the planet might well have ended up with a ‘stagnant lid’ no more conducive to sustaining life than Mars or Venus

    Many astrobiologists now think this constant renewal is just as important as liquid water for the flourishing of life as we know it.

    2
    A slice through the earth. The crust and upper mantle form the brittle lithosphere which cracks into tectonic plates. No image credit.

    The theory, explains planetary scientist Adrian Lenardic of Rice University in Houston, Texas, is that the Earth’s climate has been buffered by the recycling of carbon dioxide (CO2) from the atmosphere into the planet’s interior via mineral sequestration and then out again via volcanoes. This has kept the climate temperate even as the Sun’s heat has increased in intensity by about a third since the planet’s birth. Without this buffering, Earth might have heated so much that all the water in its oceans boiled away and huge quantities of CO2 accumulated in the atmosphere, much like Venus which has an average temperature of 462°C. Or it might never have recovered from being a snowball, remaining permanently frozen.

    Among the rocky worlds we know, Earth’s tectonics are unique. Venus and Mercury have no similar geological activity. Mars might have once, but not for billions of years. So why are we so lucky?

    According to geophysicist David Bercovici, of Yale University, models show the Earth sits right on the cusp between being a world with plate tectonics and one with a ‘stagnant lid’, like modern-day Mars or Venus. Something must have kicked it in the direction that produced a geologically active world that eventually gave birth to us. Bizarrely, even as astronomers probe planets hundreds of light-years distant, geologists still can’t precisely explain what triggered the events taking place beneath our feet.

    Tectonics derives from the Greek word ‘tektonikos’, meaning to build. It points to what we do understand about the way Earth’s surface is constantly remodelled. Our planet has a rigid shell called the lithosphere that comprises the crust and a hardened upper slice of an otherwise playdoh-like mantle (see diagram). That shell is cracked into seven large plates and a number of smaller ones that float on the mantle in slow, constant motion.

    The first inkling that continents moved dates back to the 1500s, when Flemish mapmaker Abraham Ortelius noted that the eastern and western coastlines of the Atlantic Ocean looked as if they might have once fitted together like pieces from a jigsaw puzzle.

    In 1912 German geophysicist Alfred Wegener coined the term ‘continental drift’ to describe how the lands on each side of the Atlantic had become so strangely sundered, but it wasn’t until 1963 that British marine geologists Fred Vine and Drummond Matthews provided the explanation (see Cosmos 54, p48). They realised the interior of the Earth is in motion. The rock of the mantle is slightly plastic – enough so that it can rise and fall in slow, roiling motions called convection currents: hot rock rises from the depths, cools, become denser and then descends. The best analogy is a lava lamp, which uses heat from a light bulb to induce the circulation of coloured wax in liquid. While the lava lamp’s convection currents are fast enough to produce mesmerising changes of colour, the rock of the mantle moves “about as fast as your fingernails grow”, says Bercovici – at a speed of less than 10 cm a year.

    When rising currents hit the underside of the solid lithosphere, they deflect sideways, exerting drag. If that drag is strong enough, it can rip the lithosphere apart, creating new plates and making old ones move, upwelling magma filling in the gaps. When this happens at the bottom of the ocean, the result is ‘sea floor spreading’ – which is what Vine and Matthews observed. This is occurring today in places such as the Mid-Atlantic Ridge and the Red Sea Rift between Africa and Arabia.

    As the spreading crust cools, it grows denser. Eventually the leading edge furthest from the magma flow starts sinking back into the mantle, pulling the rest of the slab behind it – a process called subduction – and so completing the convection cycle. Like the wax in the lava lamp, the cycle of rising, spreading, falling and rising again is the engine that moves the plates, and with them the continents, which ride atop like rafts.

    Though these motions occur at a rate of only a few centimetres per year, that is rapid enough to make even the oldest seafloor in the world startlingly young – less than 200 million years old. Continental crust, the buoyant crud that froths to the surface as ocean crust subducts, is much older.

    The plates do not move in the same direction or at the same speed. This causes some plates to crash into each other, driving up mountain ranges, such as the Himalayas at the collision of the Indian and Eurasian plates. They can also grind past one another, as along California’s famed San Andreas Fault. Or one can dive beneath another, as occurs at the Pacific ‘Ring of Fire’ that circles the Pacific Ocean in a belt of earthquake-prone regions and volcanic activity.

    In this process, continents tend to remain on the surface. They are too buoyant to be easily subducted into the depths. But they still play an important role via a process known as ‘weathering’, which provides a vital thermostat that has helped keep the Earth temperate for billions of years.
    Tectonic thermostat: continental weathering removes 300 million tonnes from the atmosphere each year. It’s a vital part of the carbon cycle that has kept the Earth temperate.

    4
    Tectonic thermostat: continental weathering removes 300 million tonnes from the atmosphere each year. It’s a vital part of the carbon cycle that has kept the Earth temperate.

    It begins when CO2 from the atmosphere dissolves in rainwater to form carbonic acid. This breaks down minerals in continental rocks, producing calcium and bicarbonate ions that wash into the sea. Marine organisms take them up to form calcium carbonate, the building block for their shells and skeletons, which ultimately settle to the seafloor and become limestone.

    Each year the process removes about 300 million tonnes of CO2 from the atmosphere. But the carbon isn’t sequestered forever, because some of that limestone is subducted along with the seabed. It heats, melts and is incorporated into magma for carbon dioxide-spewing volcanoes to release. This also produces fresh rock for the next weathering cycle.

    What makes this process function like a thermostat is that the more CO2 there is in the atmosphere, the more carbonic acid there is in rain (and the more rapidly weathering occurs). This removes CO2 from the atmosphere more swiftly, keeping the Earth from transforming into a Venusian runaway greenhouse. Conversely, if atmospheric CO2 levels fall,weathering slows, allowing volcanic CO2 to slowly build back up. It’s a slow, self-correcting process that for billions of years has kept the Earth’s temperature within a zone that is hospitable to life.

    So what got Earth’s plate tectonics going, rather than the planet ending up with a largely inert ‘stagnant lid’ like Mars and Venus?

    The earliest Earth was all magma ocean with no solid surface to form plates, let alone plates that drift around and collide with one another. At a minimum, plate tectonics couldn’t have begun until after the Earth’s surface solidified, somewhere about 4.5 to 4 billion years ago. Just when the plate tectonics kicked in, though, still has geologists squabbling.

    If you’re seeking the earliest traces of plate tectonics, a good place to look is the Jack Hills in Western Australia.

    5
    Low and smoothed by erosion, the Jack Hills aren’t too impressive as a mountain range. But mineral crystals have weathered out of the Jack Hills and washed into streams, and these crystals tell a fascinating story about how far back in Earth’s past the oceans might have formed. (NASA image by Robert Simmon, based on Landsat data provided by the Global Land Cover Facility)
    Source http://earthobservatory.nasa.gov/Study/Zircon/
    Author Robert Simmon, NASA

    6
    At the Jack Hills. U Mass Lowell.

    To the casual traveller this range of low mountains about 800 km north of Perth is not hugely impressive. But to geologists the hills are of towering significance, containing time capsules of the world’s oldest rocks in tiny crystals of zirconium silicate (ZrSiO4).

    Zircons formed in cooling magma. Three things make them geological gems. First, they carry a date stamp of formation, based on the decay of traces of uranium trapped within them. Second, they are extremely durable; the ancient volcanic rocks that gave birth to them eroded long ago and were reconstituted into sedimentary rocks in the Jack Hills’ outcrops. Third, they bear trace elements like titanium and aluminium, which reveal the conditions of their birth.

    7
    Time capsule: Jack Hills zircon. Born 4 billion years ago, it shows earth was already churning. John Valley, University Wisconsin.

    So far these zircon time capsules have telegraphed an extraordinary message: 4.2 billion years ago they were born kilometres below, crystallising as they rose to Earth’s surface. This tells us the mantle was starting to churn at that time.

    But were these upwellings the same as those that drive modern plate tectonics? Craig O’Neill thinks not. He’s a cheery geodynamicist at Sydney’s Macquarie University who has been studying Jack Hills zircons for many years. In his view, the zircons could have been formed by localised upwellings similar to those occurring today in places like Hawaii and Yellowstone. In other words, not an Earth-wide tectonic churning but a local percolation.

    Vicki Hansen, a planetary geologist at the University of Minnesota, Duluth, has come to the same conclusion based on “greenstone terranes” found in Greenland, South Africa, Canada and Scandinavia.

    These rock assemblages, which measure a few hundred kilometres across, date back to the Archaean Eon, 4 to 2.5 billion years ago. They are interesting because the greenish granites that give them their name are mixed up higgledy-piggledy with seabed sediments in ways we never see in more recent volcanic provinces. If modern-day rocks are like the vegetables displayed at the supermarket, the greenstone rocks are like stir-fry. This, Hansen says, indicates that whatever was going on in the Achaean involved processes “fundamentally different” to those today.

    More evidence that modern plate tectonics had not geared into action until relatively recently comes from the study of the history of continental drift.

    _____________________________________________________________
    If there’s any consensus among geologists, it is that something changed about 2.7 billion years ago to kick tectonic plates in action.
    _____________________________________________________________

    Supercontinents are formed when the plate-tectonic engine drives the Earth’s land masses to merge into one gigantic block. The closest we now have to a supercontinent is Eurasia. But some remarkable detective work – using the age of rocks and magnetic signatures that mark the latitudes where they first formed – reveals at least four granddaddy supercontinents that make Eurasia look tiny.

    The most recent is Pangaea, which formed about 335 million years ago and lasted through much of the age of the dinosaurs.

    It was preceded by Rodinia (1 billion to 750 million years ago), then by Nuna (2 to 1.8 billion years ago). The earliest detectable supercontinent is Kenorland (2.7 to 2.4 billion years ago), relics of which are scattered across Western Australia, North America, Greenland, Scandinavia and the Kalahari Desert.

    8
    http://www.the-dialogue.com/en/en33-earths-supercontinents/

    The fact we can’t find a supercontinent older than Kenorland may simply mean the surviving bits are too scattered for geologists to piece back together. It’s like trying to figure out the history of a vase that has been broken and reassembled several times.

    But with supercontinent formation and break-up requiring modern-style plate tectonics, the fact we haven’t found one before Kenorland might instead be telling us that for the Earth’s first 1.8 billion years the lava lamp was not strong enough to produce anything other than localised percolations, not the continent-driving process we have today.

    9
    Iceland’s lava fields: evidence of the rift between the North American and Eurasian tectonic plates. Picture Press / Getty Images

    If there’s any consensus amongst geologists, it is that something changed about 2.7 billion years ago to kick tectonic plates into action. “There appears to have been a major event,” says Kent Condie, a geochronologist at the New Mexico Institute of Mining and Technology in Socorro.

    But what could that have been? Theories range from the mundane to the dramatic, but all require the Earth to have overcome the same basic hurdles. Either the power of the lava lamp that makes mantle currents rise and swirl must have increased or the Earth’s crust must have weakened, allowing it to break into plates; or perhaps both occurred simultaneously.

    One view, favoured by Matt Welller of Rice University, is that feedback loops in magma currents gradually built up to a level strong enough to produce self-sustaining plate tectonics via what engineers call a ‘hysteresis loop’. A hysteresis loop occurs when there is a lag between cause and effect. It is analogous to an out-of-tune automobile engine. When you press down on the accelerator, at first the engine barely reacts, then it lurches forward.

    Suppose the deep convection currents driving the Earth’s plate tectonics were to suddenly shut down. That would reduce the amount of heat that can escape, causing mantle rocks to heat up and become more plastic. Softer rocks can support more vigorous convection, so the lava-lamp effect intensifies, carrying heat more rapidly from the interior –until enough has escaped, the mantle cools and its currents slow again.

    “You can shift back and forth as you heat up and cool down, heat up and cool down,” says Julian Lowman, a geodynamicist from the University of Toronto. According to this view, the juvenile Earth experienced these on-and-off episodes on a small scale, producing the localised tectonics suggested by the Jack Hills zircons and the greenstone terrains. Then, about 2.7 billion years ago, these shifts became locked into a self-sustaining Earth-wide convection cycle.

    Hansen, on the other hand, opts for a more dramatic scenario. The event that kicked off the tectonic plates might literally have been a kick – in the form of an asteroid or comet strike. Not as big as the one that formed the Moon, but far larger than the one that killed the dinosaurs.

    She first described her theory in 2007 in the journal Geology, arguing such an object would have punched right through the crust, heating the mantle and setting currents in motion, dragging the plates along with them and starting tectonic movements. Once plates began colliding and sinking, the process expanded until it spread across the planet. “Subduction is like a virus,” the paper states. “Once begun it can easily spread.”

    Alternatively, the dramatic event might have come from below. In a 2015 paper in Nature, a team led by Teras Gerya, of the Swiss Federal Institute of Technology in Zurich, argued that hot spots on the Earth’s core could have caused plumes of hot mantle to rise beneath a continent. Under the right circumstances, they calculated, this could break up the continent and cause pieces to sink, creating a self-sustaining cycle that became plate tectonics.

    __________________________________________________
    Even the strongest mantle currents wouldn’t have triggered tectonic activity if the Earth’s crust was too strong to break into plates.
    __________________________________________________

    Yet another possibility is that something changed the distribution of heat deep within the Earth. That heat comes from two sources: the long-lived radioactive decay of atoms such as uranium and thorium trapped in the mantle; and from the core, which contains a vast reservoir of heat remaining from the formation of the Earth. Both are slowly declining as the Earth ages.

    One might think a cooling Earth would have weaker tectonics. But it’s not that simple. “There are lines of research,” Lowman says, “suggesting that plate tectonics has a better chance of manifesting itself as a planet cools.” That’s because the lava-lamp engine that drives plate tectonics depends less on how hot the Earth’s interior is as on how rapidly it can transfer heat to the surface. The faster heat is transferred, the stronger the engine, and the stronger the mantle currents that drive tectonics.

    It has been known since the 1930s that the Earth’s core has two layers: an outer one composed of molten metal, and an inner one made of solid metal. As the Earth cools, the inner core grows. In the process it releases heat energy – equal to the amount it took to melt all that material in the first place. That energy rises through the core, increasing the rate at which it heats the mantle and, ultimately, rises to the surface.

    Supporting the theory that the cooling core may power the tectonic engine, a 2015 study by Condie and colleagues in the journal Precambrian Research traced the motions of continents over the past 2 billion years. They concluded that plate tectonics have been slowly speeding up, with average plate speed nearly doubling over that time.

    But even the strongest mantle currents would not have triggered tectonic activity if the Earth’s crust was too strong to break into plates. As it was, apparently, on Mars. For Berkovici, the key factor for the emergence of plate tectonics was therefore the weakening of Earth’s crust. It might have started gradually, beginning with the type of plume tectonics reflected in ancient greenstone terranes. Each of these magma breakthroughs would have created fault lines along which rocks slipped against each other, just as they do in today’s earthquakes. These motions would have produced weak spots that might have become focal points for later breakthroughs. Bercovici compares it to repeatedly bending a paper clip. “It gets softer,” he says. “Eventually you can bend it easily.”

    Gradually these weak zones would have spread until they merged into plate boundaries similar to today’s, and the process went from local and intermittent to global and continuous. “A meteor might have gotten it started,” Bercovici says in a nod to Hansen, “but it needs these feedbacks to keep going.”

    It is easy to try to fold all of this into a nice, coherent story. It would begin with a magma ocean, followed by weak, intermittent plume-style tectonics. These would eventually reach some tipping point that shifted the process to its present state, either due to changes in the core, an asteroid impact, the accumulation of Bercovici’s weak spots, or some combination of all three. But the plethora of options suggests caution.

    We may not yet have all the pieces to the puzzle. Lindy Elkins-Tanton, director of the School of Earth and Space Exploration at Arizona State University in Tempe, remembers being a graduate student at a conference, wondering what made scientists who disagreed with her own presentation so sure of themselves.

    “I sat there thinking perhaps I just didn’t know enough yet,” she recalls. “But now, 15 years later, I see that none of us know enough. We can only make small incremental progress in this very complicated problem.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: