̽��ֱ�� of Cambridge - asteroid

Did dinosaur-killing asteroid trigger largest lava flows on Earth?

jeh98 — Tue, 12 May 2015 10:15:26 +0000

̽��ֱ��team of researchers, which included Dr Sally Gibson from Cambridge ̽��ֱ��’s Department of Earth Sciences, argue that the impact may have triggered most of the immense eruptions of lava in India known as the Deccan Traps. In a paper published in ̽��ֱ��Geological Society of America Bulletin they claim this would explain the “uncomfortably close” coincidence between the Deccan Traps eruptions and the impact, which has always cast doubt on the theory that the asteroid was the sole cause of the end-Cretaceous mass extinction.

̽��ֱ��Deccan Traps are a vast accumulation of igneous rock, and one of the largest volcanic features on Earth, located on the Deccan Plateau in India. Formed by huge lava flows, they cover an area of approximately 500,000km² and stretch across the Indian subcontinent from Mumbai to Kolkata.

“If you try to explain why the largest impact we know of in the last billion years happened within 100,000 years of these massive lava flows at Deccan … the chances of that occurring at random are minuscule,” said team leader Mark Richards, Professor of Earth and Planetary Science at the ̽��ֱ�� of California, Berkeley. “It’s not a very credible coincidence.”

While the Deccan lava flows, which started before the impact but erupted for several hundred thousand years after, probably spewed immense amounts of carbon dioxide and other noxious, climate-modifying gases into the atmosphere, it’s still unclear if this contributed to the demise of most of life on Earth at the end of the Age of Dinosaurs. “This connection between the impact and the Deccan lava flows is a great story and might even be true, but it doesn’t yet take us closer to understanding what actually killed the dinosaurs,” Richards added.

̽��ֱ��disappearance of the landscape-dominating dinosaurs is widely credited with ushering in the age of mammals, eventually including humans.

“Paul Renne’s group at Berkeley showed years ago that the Central Atlantic Magmatic Province is associated with the mass extinction at the Triassic/Jurassic boundary 200 million years ago, and the Siberian Traps are associated with the end-Permian extinction 250 million years ago, and now we also know that a big volcanic eruption in China called the Emeishan Traps is associated with the end-Guadalupian extinction 260 million years ago,” Richards said.

“Then you have the Deccan eruptions – including the largest mapped lava flows on Earth – occurring 66 million years ago coincident with the mass extinction of the dinosaurs. So what really happened?”

Richards teamed up with a multi-disciplinary group of experts to try to discover faults with his idea that the impact off the coast of Mexico triggered the Deccan eruptions, but instead came up with supporting evidence. Paul Renne, a Professor in Residence in the ̽��ֱ�� of California, Berkeley’s Department of Earth and Planetary Science and Director of the Berkeley Geochronology Center, re-dated the asteroid impact and mass extinction two years ago and found them essentially simultaneous. He also found they were within approximately 100,000 years of the largest Deccan eruptions, referred to as the Wai subgroup flows, which produced about 70 percent of the lavas that now stretch across the Indian subcontinent.

Richards and his team found pronounced weathering surfaces marking the onset of the huge Wai subgroup flows, which may indicate a period of inactivity in Deccan volcanism prior to the asteroid impact. Since the team’s manuscript was accepted for publication, new radioisotopic ages published by scientists at Princeton ̽��ֱ�� and preliminary ages from the Berkeley group have confirmed that the Wai lava flows closely postdate the asteroid impact.

“This was an existing massive volcanic system that had been there probably several million years, and the impact gave this thing a shake and it mobilised a huge amount of magma over a short amount of time,” Richards said.

“Based on the distances between erupting volcanoes and the epicentres of earthquakes, a large asteroid impact in Mexico could generate a huge earthquake (equivalent to magnitude 9 or greater) that would have enough seismic energy to shake magma chambers deep in the Earth below the Deccan and cause a sudden massive outpouring of lava, 100,000 years or so after the impact event itself,” explains Gibson.

“Our findings have broad implications for studies of past climate change, evolutionary biology, and how earthquakes might trigger volcanic eruptions.”

Inset image: Cross-sectional diagram to schematically illustrate the Deccan plume melting in the mantle beneath the Indian subcontinent 60 million years ago (from Richards et al., 2015)

Article originally published by the ̽��ֱ�� of California, Berkeley

̽��ֱ��asteroid that slammed into the ocean off Mexico 66 million years ago and killed off the dinosaurs probably rang the Earth like a bell, triggering volcanic eruptions around the globe, according to a multi-disciplinary team of scientists.

If you try to explain why the largest impact we know of in the last billion years happened within 100,000 years of these massive lava flows at Deccan … the chances of that occurring at random are minuscule

Mark Richards, ̽��ֱ�� of California Berkeley

SA Gibson

̽��ֱ��Deccan Traps in western India

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Death of a dynamo – a hard drive from space

sc604 — Wed, 21 Jan 2015 18:00:01 +0000

̽��ֱ��dying moments of an asteroid’s magnetic field have been successfully captured by researchers, in a study that offers a tantalising glimpse of what may happen to the Earth’s magnetic core billions of years from now.

Using a detailed imaging technique, the research team were able to read the magnetic memory contained in ancient meteorites, formed in the early solar system over 4.5 billion years ago. ̽��ֱ��readings taken from these tiny ‘space magnets’ may give a sneak preview of the fate of the Earth’s magnetic core as it continues to freeze. ̽��ֱ��findings are published today (22 January) in the journal Nature.

Using an intense beam of x-rays to image the nanoscale magnetisation of the meteoritic metal, researchers led by the ̽��ֱ�� of Cambridge were able to capture the precise moment when the core of the meteorite’s parent asteroid froze, killing its magnetic field. These ‘nano-paleomagnetic’ measurements, the highest-resolution paleomagnetic measurements ever made, were performed at the BESSY II synchrotron in Berlin.

̽��ֱ��researchers found that the magnetic fields generated by asteroids were much longer-lived than previously thought, lasting for as long as several hundred million years after the asteroid formed, and were created by a similar mechanism to the one that generates the Earth’s own magnetic field. ̽��ֱ��results help to answer many of the questions surrounding the longevity and stability of magnetic activity on small bodies, such as asteroids and moons.

“Observing magnetic fields is one of the few ways we can peek inside a planet,” said Dr Richard Harrison of Cambridge’s Department of Earth Sciences, who led the research. “It’s long been assumed that metal-rich meteorites have poor magnetic memories, since they are primarily composed of iron, which has a terrible memory – you wouldn’t ever make a hard drive out of iron, for instance. It was thought that the magnetic signals carried by metal-rich meteorites would have been written and rewritten many times during their lifetime, so no-one has ever bothered to study their magnetic properties in any detail.”

̽��ֱ��particular meteorites used for this study are known as pallasites, which are primarily composed of iron and nickel, studded with gem-quality silicate crystals. Contained within these unassuming chunks of iron however, are tiny particles just 100 nanometres across – about one thousandth the width of a human hair – of a unique magnetic mineral called tetrataenite, which is magnetically much more stable than the rest of the meteorite, and holds within it a magnetic memory going back billions of years.

“We’re taking ancient magnetic field measurements in nanoscale materials to the highest ever resolution in order to piece together the magnetic history of asteroids – it’s like a cosmic archaeological mission,” said PhD student James Bryson, the paper’s lead author.

̽��ֱ��researchers’ magnetic measurements, supported by computer simulations, demonstrate that the magnetic fields of these asteroids were created by compositional, rather than thermal, convection – meaning that the field was long-lasting, intense and widespread. ̽��ֱ��results change our perspective on the way magnetic fields were generated during the early life of the solar system.

These meteorites came from asteroids formed in the first few million years after the formation of the Solar System. At that time, planetary bodies were heated by radioactive decay to temperatures hot enough to cause them to melt and segregate into a liquid metal core surrounded by a rocky mantle. As their cores cooled and began to freeze, the swirling motions of liquid metal, driven by the expulsion of sulphur from the growing inner core, generated a magnetic field, just as the Earth does today.

“It’s funny that we study other bodies in order to learn more about the Earth,” said Bryson. “Since asteroids are much smaller than the Earth, they cooled much more quickly, so these processes occur on shorter timescales, enabling us to study the whole process of core solidification.”

Scientists now think that the Earth’s core only began to freeze relatively recently in geological terms, maybe less than a billion years ago. How this freezing has affected the Earth’s magnetic field is not known. “In our meteorites we’ve been able to capture both the beginning and the end of core freezing, which will help us understand how these processes affected the Earth in the past and provide a possible glimpse of what might happen in the future,” said Harrison.

However, the Earth’s core is freezing rather slowly. ̽��ֱ��solid inner core is getting bigger, and eventually the liquid outer core will disappear, killing the Earth’s magnetic field, which protects us from the Sun’s radiation. “There’s no need to panic just yet, however,” said Harrison. “ ̽��ֱ��core won’t completely freeze for billions of years, and chances are, the Sun will get us first.”

̽��ֱ��research was funded by the European Research Council (ERC) and the Natural Environment Research Council (NERC).

Hidden magnetic messages contained within ancient meteorites are providing a unique window into the processes that shaped our solar system, and may give a sneak preview of the fate of the Earth’s core as it continues to freeze.

It’s like a cosmic archaeological mission

James Bryson

̽��ֱ��Esquel pallasite from the Natural History Museum collections, consists of gem-quality crystals of the silicate mineral olivine embedded in a matrix of iron-nickel alloy.

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Low-mass planets make good neighbours for debris discs

tdk25 — Tue, 27 Nov 2012 14:00:24 +0000

Astronomers have detected massive debris discs around 61 Virginis and Gilese 581, two nearby stars that are known to host “super-Earth” planets - so-called because their mass is between that of Earth and Neptune. Debris discs are belts of comets and asteroids orbiting the star.

̽��ֱ��study, which was carried out using the European Space Agency’s Herschel Space Observatory, also reveals that debris discs are preferentially found in planetary systems with low-mass planets than in those hosting high-mass planets. This suggests that debris discs may survive more easily in the absence of planets with a very high mass, and highlights the importance of debris discs in the study of planet formation.

̽��ֱ��formation of planets, around a newly-born star, is a dynamic process than can last hundreds of millions of years. Debris discs are a by-product of the process. They consist of everything orbiting a star that is not a planet: asteroids, comets, planetesimals and the dust that derives from them. In our own Solar System, the debris disc is mainly concentrated in two belts - the asteroid belt (between the orbits of Mars and Jupiter) and the Kuiper Belt beyond the orbit of Neptune.

Debris discs were first detected in other systems during the 1980s. Several hundred are now known. Astronomers are currently using the Herschel Observatory to search for discs around a variety of stars in our Galaxy - the Milky Way - deeper and more thoroughly than was previously possible. By exploiting the telescope’s unprecedented sensitivity and resolution, it is possible to detect very faint discs and image them in great detail.

One survey using Herschel, known as DEBRIS (an abbreviation of Disc Emission via a Bias-free Reconaissance in the Infrared/Submillimetre) has now produced two studies which detected discs around a handful of nearby stars, known to host planets. These all appear to be systems with super-Earths - planets with a mass between that of our own and Neptune, which means that their mass is relatively low.

̽��ֱ��results hint that the presence of debris discs which are bright enough to be detected with current observatories could be related to whether their parent star has low-mass planets in orbit around it.

“One of the debris discs surrounds the star 61 Virginis, which is very similar to our Sun in terms of its mass, temperature and age,” Mark Wyatt, from the ̽��ֱ�� of Cambridge’s Institute of Astronomy and leader of the analysis of G-type stars in the DEBRIS survey, said. G-type stars are of the same spectral type as the Sun.

61 Virginis is also known to host at least two planets. These have masses equivalent to about five and 18 times the mass of Earth and orbit their parent star in positions much closer than Mercury is to the Sun.

“ ̽��ֱ��debris disc extends well beyond the orbits of the system’s known planets,” Wyatt said. “Since planets and debris discs occupy such different scales, one would not necessarily expect a correlation between their properties. However, material in the debris disc is also a fossil from the epoch of planet formation so it may carry information about the processes that contributed to build up the planetary system.”

Wyatt and his collaborators took a closer look at the 60 G-type stars that are nearest to the Sun. From this sample, they found 11 with planets. Five host high-mass planets, the remaining six host low-mass planets. Of the latter group, four showed debris discs, whereas this was true of none of the high-mass planet systems. This suggests that the presence of high-mass planets may hinder the survival of debris discs.

A similar result has also emerged from a second study based on M-type stars in the DEBRIS survey. These are stars with very low masses and temperatures and are the most abundant kind in the Milky Way. Until now, only one M-type star was known to possess a debris disc - the very young star AU Mic, which is about 12 million years old.

Given the lower surface temperature of these stars, astronomers expect them to retain debris discs more easily than hotter stars, where the radiation pressure may drive the debris away. However, M-type stars have a different internal structure from their higher-mass counterparts, which creates very intense magnetic fields and leads them to radiate plenty of X-rays. It is possible that both effects may disperse a debris disc.

̽��ֱ��study found a new debris disc around an M-type star, known as Gilese 581. ̽��ֱ��star is more than two billion years old, suggesting that debris discs can actually survive for a long time around M-type stars. Gilese 581 also hosts at least four planets - all with low masses at a “super-Earth” level.

Astronomers using the Herschel Space Observatory have detected massive debris discs around two nearby stars hosting low-mass planets. ̽��ֱ��discovery suggests that debris discs may survive more easily in planetary systems without high-mass planets.

Material in the debris disc is a fossil from the epoch of planet formation so it may carry information about the processes that contributed to build up the planetary system.

Mark Wyatt

ESA.

An image of the star Gilese 581 (bottom of image), with an illustration of the debris disc superimposed to show its position.

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