On February 15th, assuming you're reading this, an asteroid came close to the Earth without hitting it. In the past several years astronomers have been keeping track of asteroids that come close to the Earth. And 2012 DA14 will come closer to the Earth than any of the others they have tracked before. Just a little over 17,000 miles. That means it will be coming within the orbit of geosynchronous communication satellites.
Now this particular asteroid is fairly small, a mere 148 feet long, so only about half the length of a football field. So even if NASA had the orbit calculated wrong and it happened to hit the Earth, most of it would burn up in the atmosphere, leaving only a small bit to actually strike the Earth. Which might be bad for anyone directly under the place where it hit, but otherwise not doing too much damage.
Now bigger asteroids do generate reasonable concerns. If we were to have a two kilometer long asteroid hit the Earth, (two kilometers would be about eleven football fields), that would be enough to generate an extra harsh winter. But even that wouldn't have much of a lasting impact. Though there might be crop loss on a global scale leading to significant shortages of food.
But the asteroid that is believed to have caused the extinction of the dinosaurs was only 10-15 km in diameter. And that impact is pretty well documented. There is a significant iridium content to the layer of sediment generated at that time. And the only reasonable source for that much iridium is an impact event.
Though there are still some who don't believe the impact caused the extinction. And the fact that dinosaur diversity had been decreasing for some time before the impact, does give those having different theories as to the cause for dinosaur extinction some room to work in.
But just recently a new study has shown that the window of difference is fairly small. The new study has shown that the two events, if they are separate events, are no more than 33,000 years apart. But there are still a lot of events that could fit into that 33,000 year window, like volcanoes and epidemics. So maybe the extinction is due to more than just one thing. I'm sure that the scientists will keep working on improving our understanding of the event.
Of course the dinosaur extinction, wasn't complete. We still have some “dinosaurs” around. And those are the birds. Though the lineage of dinosaurs that birds are descended from split off long ago. With recent evidence of birdlike dinosaurs going back over 200 million years ago. A recently described fossil from China with both birdlike and dinosaur-like features has been in the news lately. Since it has features of both groups that means it is a transitional form between the two.
So if you're reading this, then both you and the birds are still around. And the scientists out there will be looking both back into the past at previous impact events, and into the future looking for the next one. But until then keep an eye on the huge numbers of dinosaur descendants that we see every day.