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The evidence that is stated above can also prove the point that says humans do it. Humans CAN build crop circles. This is proven many times. So some are better then others. There are artists better than other artists" right? Crop circles can be made in many fashions, here is the most popular one. You stick a pole in the ground, and then you put a chain on it. You walk around the pole keeping the chain taut; this gives you your radius. Now, all you have to do is push down the remaining stuff inside the radius. This doesn't seem very hard does it? That is because it is not. That also explains why so main of them show up. Sure, some are more "accurate" than others. So what, some people are just more creative. Humans can and do make crop circles. This is the simple fact. Yet, did humans build ALL of the crop circles? This point can be debated forever, in the end it is only you that can decide what you believe.
Now that is all said and done we move on to the topic of the Pyramids of Giza. Up until a couple of hundred years ago, it was not known how these pyramids were built. The theory that aliens help build them was a popular idea. But, with the advances in science and technology, this theory is being beaten down. There is an even better, more logical theory as to how they were built. He is how it is thought it all went down. Most likely, the Pharaoh employed a workforce of up to a 100,000 (men, some of them being slaves, POWs, and what not). They would cut (very precisely) huge blocks of lime stone weighing at 2 and 1/2 tons. They would put these blocks on a row of logs and use this to push them towards the pyramids (they would also tie ropes to them and pull). They would stack these and what-not. As the pyramid got higher, they would build a spiraling ramp that started around the base and went to the top. Well, mystery solved, right?.
Now, what the afore mentioned evidence didn't explain was the intimate details of the pyramids.