Evolution is always happening. Species are constantly changing to adapt to their surroundings. If evolution wasn't always happening, many different species would have died.
Evolution is the change in allele frequency over time in a population of organisms. That has and is happening.
Punctuated
Evolution is routinely observed both in nature and in the lab. Even several speciation "events" are on record.
The theory predicts that evolution will happen and in certain ways. The observed evolution makes this prediction correct. It also defines evolution as happening, and as such is perfect evidence in support of it.
benchod
keep from happening
One word: extinction. As long as life exists, organisms will reproduce with variation - which means per definition that evolution will occur. The only way for evolution to stop happening is for life to cease existing.
Evolution doesn't take 4.2 billion years. It takes forever and no time at all. Where life is, there evolution is happening, and it will continue to happen as long as life exists.
I believe you are referring to microevolution and macroevolution. These theories both support evolution, but each in their own way. Microevolution is the most common belief today. This states that evolution is happening so rapidly that we don't even notice it. The mutations needed for evolution happen so quickly and on such a small scale that we never realize it's happening until afterwards. Macroevolution is exactly the opposite. This states that the mutations take so long that we never notice it. Both theories, in fact, were proposed because people were asking why, if evolution actually did take place, we could never see it happening.
keep from happening
prevent