http://www.dailymail.co.uk/sciencetech/article-2297594/Were-dinosaurs-killed-comet-New-analysis-suggests-smaller-faster-space-rock-sparked-mass-extinction.html?ito=feeds-newsxml
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Study claims there's not enough debris to account for
massive asteroid
For a smaller rock to cause such a huge crater it would have
to be faster
Long-period comets hurtling in from outer space fit the
bill, it is claimed
The extraterrestrial object that slammed into the Earth
65million years ago and sparked the extinction of the dinosaurs was most likely
a speeding comet, new analysis claims. New research has suggested that the 110
mile-wide Chicxulub crater in Yucatan, Mexico, was caused by the impact of a
smaller object than previously thought. But for a smaller object to have caused
such a cataclysmic impact it must have been moving at speeds usually only
reached by comets hurtling through our solar system from outer space.
It has hitherto been claimed that the the culprit was a
large, relatively slow-moving asteroid, the disintegration of which left a
global layer of sediments enriched in iridium. But at the 44th Lunar and
Planetary Science Conference in Woodlands, Texas, researchers from New
Hampshire's Dartmouth College suggested that the amount of debris left by the
collision indicates the object was much smaller. Their research suggests frequently cited
figures overstate the amount of iridium left behind by the impact, BBC News
reports.
Comparison with quantities of osmium left behind by the
impact led them to deduce that the collision left less debris on Earth than has
previously been supposed - suggesting a much smaller body was involved. But for
a smaller space rock to have produced a crater the size of Chicxulub, it must
have been travelling at speeds more consistent with a comet careering through
our solar system from outer space. Dr Jason Moore, from Dartmouth College, told
BBC News: 'You'd need an asteroid of about 5km diameter to contribute that much
iridium and osmium. But an asteroid that size would not make a 200km-diameter
crater.'
'So we said: how do we get something that has enough energy
to generate that size of crater, but has much less rocky material? That brings
us to comets.' Professor Mukul Sharma, also of Dartmouth College, added: 'You
would need some special pleading for an asteroid moving very rapidly - although
it is possible. 'But of the comets and
asteroids we have looked at in the skies, the comets are the ones that are
moving very rapidly.'
THE EFFECT OF THE
IMPACT
Whatever struck the Yucatan peninsula 65million years ago,
the impact would have caused some of the largest megatsunamis in Earth's
history. As the impactor ploughed into
our planet's crust a cloud of super-heated dust, ash and steam would have
spewed from the impact site. Excavated material, along with pieces of the
impactor, ejected out of the atmosphere by the blast, would have been heated to
incandescence upon re-entry, broiling the Earth's surface and igniting
wildfires.
Colossal shock waves would have triggered earthquakes and
volcanic eruptions across the entire world. Dust and particles could have
covered the entire surface of the Earth for several years, possibly a decade,
making the environment harsh and inhospitable.
The shock production of carbon dioxide caused by the destruction of
carbonate rocks would have led to a sudden greenhouse effect.
Over a longer period, sunlight would have been blocked from
reaching the Earth's surface by the dust particles in the atmosphere, cooling
the surface dramatically. Photosynthesis
by plants would also have been interrupted, affecting the entire food chain.
Thought to originate in the Oort cloud, a hypothesised spherical cloud of icy
bodies in the outer Solar System, long period comets follow highly eccentric
orbits around the Sun.
It is thought that gravitational perturbations caused by
either the massive outer planets or passing stars periodically send them
plunging towards inner Solar System at tremendous speeds. The mass-extinction
event 65million years ago that killed off 70 per cent of the world's species -
most notably the dinosaurs - is now widely believed to have been caused by the
impact at Chicxulub. The impact would have caused some of the largest
megatsunamis in Earth's history, as well as sending a cloud of super-heated ash
and dust into the atmosphere.
Colossal shock waves would have triggered earthquakes and
volcanic eruptions right the way across the planet. Other researchers were
cautious about the claims of the Dartmouth duo. Dr Gareth Collins, who
researches impact cratering at Imperial College London, expressed doubts as to
whether geochemistry could be used to accurately determine the mass of the
object which struck Chicxulub. He suggested that some of the mass of the object
could have landed close to the crater, or even been ejected from the Earth back
out into space, skewing the results. 'The authors suggest that 75 per cent of
the impactor mass is distributed globally, and hence arrive at quite a
small-sized impactor, but in reality this fraction could be lower than 20 per
cent,' he told BBC News.
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