IT WAS once suggested, to illustrate the chaotic and unpredictable way in which natural systems behave, that the beat of a butterfly's wing in China could eventually trigger a hurricane in the Atlantic. A bit of an exaggeration, perhaps, but the point was that even in the theoretically deterministic world of Newtonian mechanics, only a small amount of complexity is needed to make practical prediction well nigh impossible.
Thus it is perhaps not as far-fetched as it sounds to suggest that the collision 160m years ago of two space rocks, albeit quite large ones, resulted in the stormy death almost 100m years later of the dinosaurs and many other species on Earth. For although the orbits of the planets look to astronomers like a model of regular, Newtonian clockwork, on a scale of millions of years, the solar system is every bit as chaotic as the Earth's weather.
Around 65 million years ago, one 10-kilometre-wide piece crunched into Earth, unleashing a firestorm and kicking up clouds of dust that filtered out sunlight. In this enduring winter, much vegetation was wiped out and the species that depended on them also became extinct. Only those animals that could cope with the new challenge.
The trace of the great event, called the Cretaceous/Tertiary (or K-T) extinction event, can be seen today in the shape of a 180-kilometre-diameter impact crater at modern-day Chicxulub, in Mexico's Yucatan peninsula.
The trio of researchers – William Bottke and David Nesvorny of Southwest Research Institute in Colorado, U.S. and David Vokrouhlicky of the Czech Republic's Charles University in Prague – took their theory a stage further and checked out sediment samples from the Chicxulub site. They found traces of a mineral called carbonaceous chondrite, which is only found in a tiny minority of meteorites, as the Earthly remains of plummeting asteroids are called. Most asteroids can be excluded from the Chicxulub event, but not Baptistina-era ones, they contend.
Putting simulation and chemical evidence together, the team rule out theories that a comet was to blame rather than an asteroid, and say there is a "more than 90 per cent" probability that the killer rock was a refugee from the Baptistina family.
The investigators also argue that there's a 70 per cent chance that a four-kilometre-wide Baptistina asteroid hit the Moon some around 108 million years ago, forming the 85-kilometre crater Tycho.
An important point raised by the study "is how severe the repercussions of cataclysmic collisions in the asteroid belt can be for the Earth–Moon system," commented geologists Philippe Claeys and Steven Goderis of Vrije University in Brussels, Belgium, in an accompanying commentary also in Nature.
"The terrestrial impact record needs to be scrutinized more closely to identify and understand these periods of more intense bombardment, and to link them to the huge and dangerous game of billiards continuously being played out between the orbits of Mars and Jupiter," they said.
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