The Mysterious Yonaguni Monument - Artificial or natural?

In 1986, Japanese divers in the Ryukyu islands stumbled...er, swam... across a unique rock formation under the water that appeared to have been carved by some ancient civilization. The massive stone seemed to have been fashioned in a shape reminiscent of the stepped pyramids of Sumeria and Meso-America. In Japan, it was big news. In the United States, nobody talked about it.

In 1995, an even bigger structure like the one from 1986 was found off the coast of a Ryukyu island called Yonaguni. Apparently, it was the most popular news story in Japan for a year. A huge 'platform' of rock was discovered with what appear to be tiered ramparts, streets, and holes for wooden posts. At first, Japanese archeologist Masaaki Kimura thought the natural rock formations were probably a natural phenomena. After diving down himself, however, he changed his mind. Here are photos of what he saw:

In total, eight under-sea sites like this one have been found surrounding Japan.  American scholars have been loathe to address the existence of these stone monuments. If the stones have indeed been altered or the structures built by man, then scholars would be forced to rewrite their idea of human history. Why? It has been estimated that these stone structures have been submerged for 8,000 - 10,000 years. That means that during the stone age, there would have been an advanced civilization in Asia -- 5,000 years before the Egyptian empire! It would bother American historians for something amazing to be true. They are rather attached to their dogmas.

So I've said it. I believe that those shapes are quite evidently the result of the work of human hands. Professor  Robert Schoch of Boston University, who decided to meet with Kimura and make the dives to the monument, has stated that there is no reason to believe they are man-made. I don't know what his reasoning is, but he is supposedly an expert on geology. 

Here is one more piece of evidence that something like the Yonaguni monument exists and is known to be manmade: the Macchu Picchu ruins.

To me, these show how possible it is for Yonaguni to be the remnants of a powerful, ancient civilization. But what do you think? Feel free to comment!