The idea of dinosaurs being wiped out by a killer asteroid is a very new one. It captured the public’s imagination and became so well known that we sometimes forget that it hasn’t yet had time to be fully tested and proven, no matter how much its proponents claim otherwise (Scientists are only human, after all!). Until recently, the leading alternative theory was super-volcanic eruptions, which would have similar effects (massive devastation, clouds of ash and dust blotting out the sun over the entire planet for several years, everything dying of starvation, and so on).
But recently a panel of 41 experts from around the globe analysed all the data collected so far to try and settle the issue once and for all. Their conclusion? It was an asteroid, some fifteen kilometers across, which struck the Earth at Chicxulub, Mexico, leaving a crater 100km across (so large that you need satellite imagery to see it!), with a force one billion times that of the atomic bomb used at Hiroshima. So now we can all rest easy knowing that such things have happened, and could happen again!