Write a paragraph to refute a claim by a colleague that ancient structures such as Stonehenge, the Great Pyramid are evidence of UFO activities on Earth 
 There are several strong arguments against concluding that alien races built the structures like the Stonehenge or the Pyramids. First, there is evidence that these magnificent structures were built by humans. For example, tombs of the pyramid builders were found in the vicinity of the Great Pyramind (with human remains!). The technology to move and assemble the massive stones of the Stonehenge has been shown to be available to humans at that time. Second, given that space is vast the chance of finding one tiny planet among billions is infinitesimal. If alien intelligence had indeed found our one inhabited planet they are unlikely to have just created couple of structures and avoided any further contact with Earth and its inhabitants. In science, Occam’s Razor (“the best explanation is the simplest one”) is a guiding principle and until there is much more evidence of alien visitation it would be inadvisable to jump to a conclusion that aliens built these structures.