[Guys, I was looking at the Forerunner information, and it explains how the Forunners are really humans who destroyed themselves by activating all the Halo's from The Ark. 343 Guilty Spark says so..Here, please read this!
Near the end of Halo 2, 343 Guilty Spark explains that the Forerunner destroyed themselves along with other sentient life within three radii of the galactic center by activating the Halo weapons from The Ark. The Ark is believed to be on or near Earth; it is unknown whether it encompasses the entire Earth or is simply an installation or object located on Earth. The Ark's nature will not be revealed until Halo 3, but theorized locations for the Ark include New Mombasa, East African Protectorate (from Halo 2), Jerusalem, and Boston, Massachusetts (from the Haunted Apiary). Some have also suggested that the Ark may in fact be located on or in the Earth's moon.
It is also theorized that the humans may actually be Forerunners who were protected from the original activation of the Halo weapons, possibly by The Ark, just as Noah's ark saved life from God's flood. This can be speculated also from a number of comments by 343 Guilty Spark in the novelization of Halo: Combat Evolved ("Halo: The Flood" by William C. Dietz). After being teleported to the Library by Guilty Spark, the Chief asks where he is, to which the Monitor replies: "The installation was specifically built to study and contain the Flood. Their survival as a race was dependent on it. I am grateful to see that some of them survived to reproduce." This is apparently a reference to the Forerunner. If it is in fact a reference to the Forerunner, it could very well mean that the humans are the Forerunner and would explain why the Master Chief, Miranda Keyes, and possibly all humans, are considered Reclaimers. 343 Guilty Spark might very well consider the humans there to reclaim the ring itself. Also, after the retrieval of the Index, when confronted about the true function of Halo, Spark comments: "But you already know that...I mean...how couldn't you" - "Last time you asked me, if it were my choice, would I do it? Having considerable time to ponder your question, my answer has not changed." This not only shows that the Forerunner destroyed themselves with the Halo weapons, but that the Master Chief, as a human, is mistaken for one of the builders of Halo. Basically, Guilty Spark thinks that the Chief is a Forerunner. In addition it may explain why humanity is found on Earth; however, the human/Forerunner relationship is only speculation. This may also explain why the AI cortana says in both Halo and Halo 2, that somthing seems 'familiar' about the forerunner computer systems. Another theroy supports this in saying that the humans may have sent the Halos back in time to several million years before (the human covenant war)and so cortana may have very well created the system. this also would explain how the Master Chief knows how to use the systems on Halo.]