Science & Environment  Dinosaur-killing space rock 'was a comet'
Chicxulub impact Image caption The impact 65 million years ago
killed off 70% of species on Earth - including the dinosaurs
The space rock that hit Earth 65m years ago and is widely
implicated in the end of the dinosaurs was probably a speeding
comet, US scientists say.  Researchers in New Hampshire suggest
the 180km-wide Chicxulub crater in Mexico was carved out by a
smaller object than previously thought.  Many scientists
consider a large and relatively slow moving asteroid to have
been the likely culprit.  Details were outlined at the 44th
Lunar and Planetary Science Conference.  But other researchers
were more cautious about the results.  "The overall aim of our
project is to better characterise the impactor that produced the
crater in the Yucatan peninsula [in Mexico]," Jason Moore, from
Dartmouth College in New Hampshire, told BBC News.  The space
rock gave rise to a global layer of sediments enriched in the
chemical element iridium, in