The impact hypothesis was controversial for many years, even after the Alvarezes published their findings in 1980 about iridium deposits that were almost impossible to explain any way other than an asteroid impact. Some scientists still favored existing hypotheses, including volcanism, sea level changes, and even chronic constipation. (See Keith M. Parsons' "The Great Dinosaur Controversy" published in 2003.)
Many scientists believed that major collisions between celestial bodies ceased long before the dinosaurs went extinct. It wasn't until 1994, when Shoemaker-Levy 9 crashed into Jupiter, that we witnessed such an event occuring. 100% undeniable proof that collisions still occured, which meant they definitely could have occured 65 million years ago.
There was also the problem of the impact crater. The original 1980 paper was based on iridium deposits around the world, but there was no known impact crater of sufficient size that could be dated to the right time. The Chixulub crater was discovered in the 1970s, but it wasn't identified as an impact crater until 1990. (Previously, it was thought it may have been a volcanic caldera.)
All this is to say, evidence has trickled in to support the impact hypothesis, and while the pieces were there in the 90s, it has taken some time to put them all together.
And the discussion isn't over either! While many experts got together and concluded in 2010 that an asteroid impact was the main cause of the K-Pg (formerly K-T) extinction event, there is still significant evidence that volcanism at least played some part. The dinosaurs may well have been on the decline for a long time, and the impact simply sealed their fate. Anyone who says "the asteroid killed the dinosaurs" is probably oversimplifying a complex issue, but it would be a huge mistake the ignore the asteroid impact altogether.
Source: A 2015 essay I wrote as an assignment covering a controversy in science during my undergraduate studies.
IAmTheFloydman t1_j4tzqs1 wrote
Reply to Extinction of the Dinosaurs: What did I miss? by cakedayCountdown
The impact hypothesis was controversial for many years, even after the Alvarezes published their findings in 1980 about iridium deposits that were almost impossible to explain any way other than an asteroid impact. Some scientists still favored existing hypotheses, including volcanism, sea level changes, and even chronic constipation. (See Keith M. Parsons' "The Great Dinosaur Controversy" published in 2003.)
Many scientists believed that major collisions between celestial bodies ceased long before the dinosaurs went extinct. It wasn't until 1994, when Shoemaker-Levy 9 crashed into Jupiter, that we witnessed such an event occuring. 100% undeniable proof that collisions still occured, which meant they definitely could have occured 65 million years ago.
There was also the problem of the impact crater. The original 1980 paper was based on iridium deposits around the world, but there was no known impact crater of sufficient size that could be dated to the right time. The Chixulub crater was discovered in the 1970s, but it wasn't identified as an impact crater until 1990. (Previously, it was thought it may have been a volcanic caldera.)
All this is to say, evidence has trickled in to support the impact hypothesis, and while the pieces were there in the 90s, it has taken some time to put them all together.
And the discussion isn't over either! While many experts got together and concluded in 2010 that an asteroid impact was the main cause of the K-Pg (formerly K-T) extinction event, there is still significant evidence that volcanism at least played some part. The dinosaurs may well have been on the decline for a long time, and the impact simply sealed their fate. Anyone who says "the asteroid killed the dinosaurs" is probably oversimplifying a complex issue, but it would be a huge mistake the ignore the asteroid impact altogether.
Source: A 2015 essay I wrote as an assignment covering a controversy in science during my undergraduate studies.