After having read through the responses already made, I think people ahve already covered what is necessary. I would like to give another analogy that might help you understand the difference between the two terms.
Just look at history. We generally divide human history up into large intervals like the stone age, the bronze age, the iron age, etc. There are individual moments in history when it is bleedingly obvious to us what era it belonged to. Alexander the Great was clearly in the late bronze age. The Crusades were clearly in the Iron Age. It's like looking at the color spectrum that jar presented. There are areas where it's bleedingly obvious if it's blue, red, or yellow.
However, asking the question of when microevolution becomes macroevolution is like asking exactly when did the world turned from the Bronze Age to the Iron Age. Noone could answer that. Very tiny changes in the way tools and weapons were made and used eventually added up and gave rise to the Iron Age. But can anyone actually say the exact year, date, hour, or minute the world emerged into the Iron Age?
In a way, microevolution is just referring to very tiny changes in the allele frequency of a species. Say that you start with generation 0. Generation 1 is still almost genetically identical to generation 0. Generation 2 is still almost genetically identical to generations 1 and 0. We jump to generation 300 where the allele frequency is now noticably different than generation 0 and 1, but they are still the same species. We jump to generation 3000 and the differences are a little more noticable if we compare to generation 0.
But notice that generations 3000, 3001, and 2999 are almost genetically identical to one another. It's when you compare them to generation 0 or 1 that you notice a difference. But again, they are still the same species.
Fast forward in time and now we are at generation 300,000 and we already have a new species because this generation is genetically different than generation 0 and that they can no longer interbreed. But hang on a second, when did this population make the "transition" that changed to a new species? Was it generation 102,845? Was it generation 142,893? Generations 100,000 and 100,200 are still almost genetically identical. But when you compare generation 100,000 to 0, there are very noticable differences. Compare generations 300,000 to 0 and they are obviously different species.
Now, saying that we can't know what's what in the past is simply silly. We can look at archaeological evidence and determine about what age so-and-so city was burned to the ground. We can look at the tools, art, houses, etc. left behind by people long gone and determine how these people lived and died. In similar ways, we can look at the fossil record and determine things that were far far in the past.
Neutralmind writes:
Also, I want all of you to write more questions because I'm seriously not a specialist in this.
From what I've seen from you in other threads and this particular sentence, I can tell that you still hold a grossly deformed idea of what evolution is all about. "Macro"evolution doesn't mean a fish one day decides to grow 4 legs and become a lizard or a cow one day decides to grow a pair of wings and become a bird. Despite the fact that we've been trying to explain the very slow and tiny progression of changes that over millions of years would add up to very large changes, people like you and Ann Coulter continue to make arguments like how come we don't find a fossil of an animal half cow and half eagle as a transition. I recently read Coulter's new book and she made almost the exact same stupid and grossly uninformed argument against evolution. If you've seen frustration somewhere along the line from one of us, please understand that it's very frustrating for us to repeat the same thing over and over to the same goddamn people and a few months later see the same bogus arguments from the same goddamn people. Ann Coulter contributed a whole chapter essentially calling all scientists dumbasses, and I think she and her ilk shouldn't be shot... flu shot that is.
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