One partial definition is that organisms change, by genetic mutation, and survive to produce offspring. But it is easy to see change in organisms in our lifetime. Or bacteria that have become resistent to antibiotics. In the Grand Canyon there are squirrels that live on the north and south side of the river, and they are different from one another, but are thought to be from common ancestors. In the geologic record there are very many fossils of animals which seem to have changed over the course of a very long time.
Mammoth fossils show a big change in tusk size over a long time period.
Most scientists agree that some kind of evolution has occurred over time because of the many different pieces of evidence there are. But not everyone agrees about why this change occurred or how it occurred. It is very interesting that plutos orbit is so different from the other planets. Pluto may even be an object that was captured by our solar system from somewhere else. It is not likely that Pluto and Neptune will crash, since they are really very far apart, and take a long time to get around the sun.