We are, it is claimed, living in the aftermath of the breakup of a giant comet in the inner Solar System. This event may have been associated with the most recent Ice Age, which began about 100,000 years ago. It produced a stream of Sun-orbiting material linked with the Taurid meteor stream, which peaks around 30 June in daylight hours but is visible as 'shooting stars' in the night skies of November. The Earth passes throught the thickest part of this belt of debris every 3,000 years, and there is evidence that this happened most recently in AD 500 and before that in 2,500 BC On both occasions, Tunguska-like events would have been common, with one impact in each region the size of England over a period of a hundred years or so.
Gribbin and Gribbin:1996:xii

Some geologists fought a rearguard action against the impact hypotheses, arguing that the kind of evidence being turned up by the renewed global interest in the K-T boundary in the 1980s could all be explained in terms of volcanic activity. They pointed out that there had been a massive episode of volcanic activity in what is now India, producing huge sheets of volcanic material known as the Deccan Traps, at about the right geological time. This may well have had a widespread environmental impact. But although some volcanoes do emit traces of iridium, most do not; and no volcano produces shocked material like the quartz grains and stishovite found in the boundary layer, or tektites.
The clinching blow to the volcano hypotheses came when the supporters of the impact theory quickly realised that a very good way to trigger a massive burst of volcanic activity would be to hit the Earth with a large meteorite. The shock waves from such a blow might well have triggered activity at weak spots in the Earth's crust. This explains the 'coincidence' of the volcanic activity with the meteorite impact, and added to the difficulty of life at the end of the Cretaceous.
One thing you certainly don't get out of volcanic eruptions is the kind of complex chemical compounds known as amino acids. But there are even traces of amino acids at the K-T boundary layer-31 different amino acids in all, 18 of which have been found nowhere else on Earth, but all of which are known to be present in interplanetary material such as meteorites.
Gribbin and Gribbin:1996:21

But it (Chicxulub) wasn't alone. The Manson impact structure was formed at the same time, and geologists have also found another crater 65 Myr old: a multi-ringed impact side 100 km across at Popigai, in Siberia. Were the dinosaurs actually wiped out by a triple whammy? It looks very likely. Indeed, this may be a conservative assessment, since there are several other features of about the right age (but not yet dated accurately) in a line linking these sites. They include an impact structure 20 km across at Avak in Alaska, a pair of craters at Kara in western Siberia, and others. To eyes that have seen the photographs of the impact of the pieces of Shoemaker-Levy with Jupiter, this is highly intriguing.
But let's becautious, and concentrate on the three well-dated simultaneous impacts. If they were produced by fragments of a comet that broke up as it passed near the Sun, astronomers can even infer the time of day and the season in which the impacts occurred. For the three pieces of interplanetary debris, travelling nearly together throught space on their way out from the Sun, to strike simultaneously in Yucatan, Iowa and norther Siberia, it must have been summer in the northern hemisphere, with the north polar regions tilted towards the sun and offering an inviting target. And since the pieces of comet were coming directly from the direction of the Sun, striking the side of the Earth facing the Sun, the impact must have occurred about midday, probably out of a clear blue summer sky. There is even independent confirmation of the time of year when disaster struck, in the form of plants ina fossilised lily pond in Wyoming, which have been dated to the K-T boundary and which died at the stage of growth corresponding to early June. . . .
Gribbin 1996:32,33

Gribbin and Gribbin:1996:32,33

carbon fullerenes
Gribbin and Gribbin:1996:36

"The information we have about the surface topography of Venus comes mainly from the spaceprobe Magellan, which went into orbit around the planet at the beginning of the 1990s, and mapped almost the entire surface by radar. The radar maps show that Venus is a hightly active planet, covered by volcanoes and lava flows, with a cracked, tortured surface. Over all of the surface there is also a uniformly random pattern of impact craters. But there are far fewer craters than there would be if, like Mercury and the Moon, Venus had retained its ancient surface layer. From comparison with the number of craters on Mercury and the Moon, astronomers infer that the entire surface of Venus was wiped clean in some great cataclysm about 600 million years ago. Geologists describe this event as having 'resurfaced' the planet with lava from its interior, as great blocks of the surface cracked and subsided; in all probabliily such events have occurred several times in the 4 billion years or so since Venus formed."
Gribbin and Gribbin:1996:72,73