Today it is widely accepted that the extinction of the non-avian dinosaurs was caused by the giant meteorite impact at Chicxulub, Mexico; this has not always been the received wisdom, however. Fifty years ago it was thought that the enormous amount of volcanic activity of the Deccan Traps was what wiped them out. The reality could be that it was actually a combination of the two, a one-two killer blow, that actually did for them.
The Deccan Traps are a vast basaltic flood in what is now India. Over the course of about 10 million years or so they spewed out enormous, climate changing quantities of basalt lava and toxic gases.
No matter what new information follows the lava out of the ground at the Traps, the impact at Chicxulub is not going anywhere. It has been well characterised and was certainly a major driver behind the mass extinction at the K-T boundary. It was a truly global event as evidenced by the layer of iridium found all over the globe at exactly the right point in all strata studied.
The Deccan Traps, though, had already been erupting for a million years before the impact occurred and, perhaps, this could account for recent evidence that many species started to go extinct before that point. What would be very interesting to know is whether or not the meteorite made the eruptions worse. One theory suggests that the sheer shock of the impact started the earth ringing like a bell and these vibrations could have worsened or otherwise prolonged the eruptions.
The exact balance of responsibility for the mass extinction of 66 million years ago is still a matter of scientific debate. Two generations ago it was 100% Deccan Traps; one generation ago it was 100% Chicxulub. Now, it seems more likely that it was a mix of the two, maybe 80:20 in favour of the impact. Like most things worth knowing, everything gets a little more complicated the more you look into it.