On the west coast of India , near the city of Mumbai , lie a excruciate landscape painting . Faults score the flat coat , earthquakes are rife , and boiling piss oozes up from below form countless red-hot spring . These are testaments to a traumatic history .
Further inland , stark stack of volcanic basalt provide compelling grounds that this intact region – an area of some 500,000 square kilometres bonk as theDeccan traps – underwent turn of volcanic action between 68 and 64 million years ago .
We do n’t bonk why . The Deccan traps lie far aside from any tectonic plate boundaries , those fracture in Earth ’s crust through which lava usually ram its way up from the planet ’s DoI . No volcanism on the scale implied by the Deccan yap occurs on Earth now . However , smaller , equally mystifying “ hot spot ” dot the globe away from plate boundaries – the smoke volcano of the Hawaiian islands , for example , or the bubbling geysers of Yellowstone National Park in Wyoming .
geologist have generally thought that the history of such feature film can be retrace through the slow churnings and contortions of rock under air pressure in Earth ’s mantle . But it seems there is more to it than that . Sometimes volcanic activity postulate – and catch – a helping mitt from above .
It was in the late 1960s that oil companies prospect off India ’s western coast found something unexpended in the rocks beneath the ocean story . Sediments laid down on an ocean bed over millions of year mostly mold rock’n’roll resembling a layer bar , with the layers get older the deeper you turn over . That was true in the boreholes drilled off the coast near Mumbai , to a point . But some 7 klick down , in a layer of rock deposited 65 million years ago , the corking progression short stopped . Beneath it was a layer of shattered rock , stick to by a stratum of solidify volcanic lava up to 1 km thick .
Something as dramatic lurked onshore in the layered lava flows of the Deccan traps . These flow are interrupted by average stratum of sedimentary sway , indicate that the volcanic activity that shake and remodelled the area from about 68 million years ago was not uninterrupted . It was also not catastrophic ; fossil encounter in the sedimentary level intimate that dinosaurs had coexist with this activity reasonably well .
But settle down in layers of lava dating from 65 million years ago – around the sentence dinosaur disappeared from Earth ’s dodo record – are stupendous spires of lava of a essentially dissimilar paper . These spires are up to 12 kilometres in high spirits and 25 km across at their base , so that their tips appear as control surface hills . The lava they are made of is extremely alkaline and copious in atomic number 77 , an element rare in the Earth ’s Earth’s crust but which commonly occurs in meteorites . The lava in the Deccan traps is rich in iridium , an element rare in the Earth ’s crust but which commonly occurs in meteorite
To palaeontologistSankar Chatterjeeof Texas Tech University in Lubbock , all of this was telling a news report . In 1992 , he recounted it to the world : the full washstand area off the coast of Mumbai , he exact , was a Brobdingnagian undersea impact volcanic crater , some 500 kilometres across , form when a meteorite 40 kilometres in diam slam into Earth 65 million years ago and convulsed its control surface . He name the crater Shiva , after the Hindu god of destruction and renewal , and touted it as the big brother ofChicxulub , a volcanic crater 180 km across under the Yucatán peninsula in Mexico , which date to the same sentence .
This claim was adhere to stir controversy . The aftermath ofthe Chicxulub impact supposedly did for the dinosaursand many other species that disappeared in a wave of extinctions around that metre . If Chatterjee was correct , Chicxulub was unlikely to be the whole level .
Most geologists were unconvinced . For a starting signal , the Shiva crater was simply too large . Whereas massive impacts were common in the rambunctious early Day of the inner solar organization , the absence seizure of recent large volcanic crater on Mercury , Venus and Mars powerfully suggests that those days are long gone . “ These airfoil show that objects larger than 30 kilometre have not produced impacts in the last three billion year , ” says wandering geologistPeter Schultzof Brown University in Providence , Rhode Island .
Chatterjee answer that there are still object of the veracious size of it out there , for example thenear - Earth object1036 Ganymed that NASA is monitoring tight , although it is happily not on a collision course with Earth . Moreover , he say that studies off the Indian sea-coast by oil companies in the nineties revealed gravitative anomalies that add weight to his argumentation .
The exact strength of the gravitative deplume an physical object feels at the Earth ’s surface differ from place to office . It is weaker in areas dominated by low - density granite rocks , for example , and stronger where high - density basalt rocks dominate . If you cross from one side of the posited Shiva volcanic crater to the other , the gravity sign weaken towards the eye before reversingand becoming much stronger again towards the proposed rim .
That , says Chatterjee , squares with the estimation that a meteorite run into what is now the Mumbai coast from the due south - east at an devious slant of 15 stage to the horizontal , obliterating the crust entirely and scraping away a portion of the upper mantle , too . The impact would have thrown up a granite peak 50 kilometres in high spirits that crumple back down through a pool of rock candy below that had been melted in the impact .
That would explain not only the anomalous area of lower gravity under the ocean , but also the odd geology of the Deccan traps . As the granite peak collapsed it too meld , causing the impact crater to run over and creating enormous melt ponds of alkaline , iridium - rich lava in the charred surroundings . Meanwhile , the seismic disturbance of the impingement caused the moderate Deccan volcanic eruption , already occurring nearby , to go into overdrive . “ A lava drip became a torrent , ” says Chatterjee . This soaker of normal lava enclosed the iridium - productive lava overspill from the impact , bring forth the sensational enclosed steeple computer architecture seen in the Deccan layers today .
That is at best half an answer : it does not explain where the Deccan volcanic activity came from in the first place . Many palaeoscientists , admit Chatterjee , think this was linked toa hotspot currently dynamic under the island of Réunion in the Indian Ocean . This hotspot may well have been beneath the surface area of the Deccan trap 68 million years ago , before continental purport impress them apart .
Even so , it is a contentious call : to suggest that impacts can amplify volcanic activeness is to give them a far greater influence on Earth ’s late geological history than has conventionally been allowed . The effect might not just be volcanic , either . According to Chatterjee ’s calculations , the military group of the impact could have been enough to open up a new breach in Earth ’s crust to the western United States of the crater , stimulate a tiny sliver of westerly India to transmigrate out into the sea as new oceanic crust forced its way up . The most obvious sign of such a detach paring today lies almost 2800 kilometer south of the Indian mainland – the island grouping of the Seychelles .
Comparison with other wallop sites register that if the Shiva volcanic crater exist and if it is as freehanded as proposed , the shock would indeed have released enough vigour to have such effects . “ The physics of the process is undeniable , ” say geophysicistAdrian Jonesof University College London . Even if the Shiva impact never happened , in a startling turn it seems an impact could well have caused the monolithic Deccan eruptions .
To understand how that might be expect an abrupt change of view , to the frozen permafrost of northern Siberia . This region hold in a huge surface area of volcanic rock just as rummy as the Deccan trap – and , at some 2 million straight kilometres , roughly four times the size . These Siberian traps contain slab of lava up to 3 klick buddy-buddy that were formed in a single result 251 million year ago .
For geochemistAsish Basuat the University of Rochester in New York , this was entrancing , not least because the lava ’s date tallies with the largest mass experimental extinction eff , thePermian - Triassic extinction , in which over half the subsist beast families died out .
Where did so much lava come up from over such a short period ? When Basu dissect the chemical opus of the rock to find out , it bemuse up a surprise . The lava show abnormally in high spirits engrossment of the isotope helium-3 , generally a signature of rocks from far down in Earth ’s interior . “ Something was causing the rich mantle to derive up , but we did not acknowledge what , ” says Basu .
A hole plug by an wallop , perhaps ? Basu was aware of Chatterjee ’s piece of work , and it was tantalizing to float a connection between two Brobdingnagian unexplained lava flows , each dating from the same clip as a deal quenching . So Basu travelled to India to do his helium analytic thinking on the rock there , too . He came up with the same anomalous result .
For Basu , that only deepen the enigma . For one thing , there was no noticeable encroachment site anywhere near the Siberian lava flows . For another , he was not convince that the Shiva site was actually an impact crater .
His brainwave was that it did n’t weigh . “ A big impact anywhere would have shake the planet and created pressure that might have amplified rich - mantle volcanic activity already in advance , ” he says . If that was so , whether Shiva was an impact crater or not was irrelevant . An encroachment anywhere in the world could have been the trigger for the Deccan volcanism ; arguably , it could even have been the well - document Yucatán impact . Shaken and stirred
Basic aperient say that is plausible . “ The idea of volcanic activeness being primed and increase by energy waves institutionalize through the drape by impacts elsewhere on the planet is a fairish one , ” say Jones . Pressure waves from temblor travel highly well through the interior layers of the Earth : seismographs in Europe and the USroutinely pick up tremors thousands of mile out in China , for case . A superpowerful pressure wave such as one create by a huge impact could well have done enough to rattle volcanic plugs and shift lava domes , activate otherwise balmy or dormant volcanism . A superpowerful pressure undulation create by a huge encroachment from space could rattle volcanic plugs and actuate dormant volcanism
To loan credence to the idea , what Basu needed was grounds of a meteorite impact 251 million geezerhood ago – not in Siberia , but anywhere . That had him stomp until 2003 , when he and his confrere were give a 251 - million - year - previous John Rock sample distribution from near the Beardmore glacier in Antarctica . Within the rock , they found inclusions with an odd chemical report that look for all the man like meteorite fragments . They published a paper detailing the exciting discovery and its possible implication : that the two with child volcanic consequence in the past billion years could have been because of meteor shock ( Science , vol 302 , p 1388 ) .
The title caused a considerable stir , and many geologists dismissed the Antarctic finding out of mitt . “ A passel of literary criticism came because folks figured it was n’t potential for meteorite fragments to last so long , ” saysEric Tohverof the University of Western Australia in Perth . Meteorites are mostly metallic and would usually be expected to rust away into nothingness over 100 million eld , even if bury . The fragment must be New , said the critics , and somehow have infiltrated the sediment .
Undeterred , Basu and his colleagues iron out on with their exploration . In March this year , at a conference of planetary scientist in Houston , Texas , they face what they consider to be a smoke gun : more meteorite fragments , this time enclosed in clay turn back fogy that see them to 251 million years ago . the Great Compromiser readily absorbs piddle , draw off moisture and forbid meteorite fragments from rusting away .
agnosticism remains . “ Small meteorites fall from the sky all the fourth dimension , ” say Schultz . “ Just because these meteorite fragments are the same age as the Siberian lava does not mean they and the Siberian lava flows are come to . ”
As deliberate as Chatterjee ’s and Basu ’s ideas are , the construct that extraterrestrial bodies might have verbatim geologic effects is now more wide accepted . “ The idea of impacts cause volcanism is absolutely plausible , ” saysVicki Hansen , a planetary geologist at the University of Minnesota , Duluth : modelling shows that impacts can readily fade a planet ’s airfoil layer where it is relatively thin .
The question is what sort of volcanic body process that might generate . Might impact aid to excuse the hot spot of Hawaii and Yellowstone , for example ? Hansen is open - minded , but sceptical . “ There can be little doubt that an impact could spawn a character of hot spot given the right conditions , ” she says . The impudence beneath Hawaii , though , seems relatively intact , and the hotspot looks to be the consequence of a bulge of superheated pall , or “ plume “ , forcing its way up for reasons unknown . We know less ofwhat underlie Yellowstone ; there is no evidence yet that an impact playact a pregnant part there .
With other hotspots it is a different story . TheOntong Java plateaulies beneath the westerly Pacific , north of the Solomon Islands , and it is a hotspot that was participating some 125 million years ago . The upper layer of the Mickey Charles Mantle are uplifted there , but not as much as under Hawaii . A likely account is that an impact fractured the freshness , allowing melt from below to get up and splatter out as an eruption . The escape of so much melt material would cut the denseness of what was leave behind , causing the mantle bulge seen today ( Earth and Planetary Science Letters , vol 218 , p 123 ) .
How long such impact - induced fireworks might have lasted is another area of debate . Tohver thinks not so long – a few hundred thousand years , perhaps a few million . “ It is a lot like dropping a spoonful into loggerheaded pea soup , ” he say : the initial large disruption would quickly die down . Schultz agrees , on the basis of studies of other solar system eubstance . “ Theoretical good example reason that impacts could not trigger free burning blast , ” he says .
Jones begs to differ , arguing that better modelling will show that free burning volcanic eruption can ensue from impacts . “ A major dispute between the Earth and our neighbouring major planet is that Earth is still very hot and geologically active , so may be much promiscuous to melt with impacts , ” he says .
The argumentation will rage on , but one thing seems sealed : accumulate grounds means the daytime of thinking about geology without considering influences from above are numbered . “ Geologists do n’t typically study encroachment hypotheses , perhaps for psychological reasons , ” articulate Hansen . “ We have been take to consider thing that come from within our planet . ” Being impel to consider the effects of random meteorite smasher adds another complexity to an already involved subject . But in the end , says Hansen , “ We are never going to get anywhere if we keep try out to sympathize our planet with our hands over our optic and ear . ”
Top mental image viaUniversity of Arizona .
This clause originally appearedon New Scientist .
Matt Kaplan is a writer base in California and the UK .
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