Crown Capital save the Earth Management: Were the dinosaurs killed by a comet?
Publisher: Rikko Lance Sebastian
Published: 2013
Place of publication: United States, Fullerton (California)
Format: Book Review
Number of pages: 1
Description: Were the dinosaurs killed by a comet? Researchers says smaller, faster space rock sparked mass extinction
•	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.