On the K/T-missile and its impact:

In one of the greatest titled books ever, T. rex and the Crater of Doom, Walter Alvarez told the story of how he and his nobel prize-winning physicist father Luis revolutionised our understanding of the end of the dinosaurs. [Walter] … discovered that the boundary layer in rocks found at Gubbio in Italy contained ten times the normal levels of the metal iridium. […] … Luis had the insight that such a high concentration of the metal in one layer of rock meant it must have arrived in one huge asteroid impact. The team then confirmed another iridium spike in a Cretaceous-Paleogene boundary rock section at Stevns Klint in Denmark. […] They reasoned that the spikes implied there had been an asteroid impact so big that it threw enough dust (including tiny particles of iridium) into the atmosphere to black out the sun around the globe. This would have prevented plants from photosynthesising and, as was later suggested, caused global freezing for a short time, leading to the mass extinction of many species. They worked out that such an asteroid would have weighed at least 34 billion tonnes and measured around 7km in diameter, producing a crater around 100–200km across. […] … However, it still took a while to locate the Chicxulub crater because it had been completely covered by sediments deposited in the previous 66m years. And while half of it lies under dense tropical rainforest, the other half is beneath the Caribbean seabed. Hildebrand used evidence from boreholes made by Mexican oil company Pemex in the 1960s to prove the crater’s existence. Subsequent geophysical surveys that can scan below the surface have established the exact size and shape of the structure, which is roughly circular with three concentric rings, as you would expect from a massive impact.