Back in the 1980s observations of a layer of sediment right when the dinosaurs went extinct led to a hypothesis of an asteroid or comet impact being the cause of the extinction. Like many hypotheses that are fairly radical, it took a while to gain acceptance, yet now it is considered the likely cause of the extinction.
There is a saying that when your only tool is a hammer everything starts to look like a nail. And this is true of scientists too. So after the dinosaur extinction was determined to have been caused by an impact from space, other scientists started to look at other extinctions and hypothesized they took were caused by some kind of impact from space.
For example, during the last Ice Age, here in North America, there was an extinction of most of the largest animals. Mammoths, horses, and saber-tooth cats are all examples of the mammals that went extinct towards the end of the last Ice Age. So some scientists started looking for evidence that there was some kind of impact that caused it, actually hypothesizing that there was an impact in the air above the ice sheet that was covering the area that became the Great Lakes.
So to check their hypothesis they started to look for evidence and found things that were consistent with an impact. Certain residues in soot found around the world at the time, for example. And nano-diamonds for another. So there has been some evidence that is consistent with the theory. Which generates more interest and then more research.
But when you do the research, sometimes you find things that are not consistent with the theory. For example, since the hypothesized impact had to affect climate around the world we should be able to look for evidence all over the world. Well one research project in Syria looked at particles formed by fire found at about the right depth. However, the results didn't indicate that the particles were formed by an impact.
This was because the particles were formed from the local soil, not soil from around the world in North America. The particles were formed at much lower temperatures that an impact would generate, and they were formed over a period of time and not a single time like an impact.
But what caused this soot and the particles? Well, these scientists looked at time they would have been formed 10,000-13000 years ago and realized that people in that region were starting to live in villages, agriculture was getting started at that time, and the formation of the soot they looked at was consistent with their mud and straw houses burning down.
So while some evidence has been found to support an impact towards the end of the last Ice Age, here's a strike against the hypothesis. So scientists will continue to investigate the cause of the extinction around 13,000 years ago. It has been a big question for many years, and they can pull other tools from their toolbox to determine what happened.