http://sploid.gizmodo.com/nasa-publishes-fascinating-book-on-how-to-communicate-w-1579396194

NASA is getting ready to communicate with aliens (Update 2)
Jesus Diaz
Yesterday 12:10am

"We can say little, if anything, about what these patterns [above] signify, why they were cut into rocks, or who created them. For all intents and purposes, they might have been made by aliens." When a new NASA book on alien communications has a paragraph like that, you better pay attention.

Update 2: NASA pulled the book and press release from their site. Now the book is available here, as pointed out by a commenter.

Of course, the scientists and scholars who contributed to Archaeology, Anthropology and Interstellar Communications—a new 300-page volume [1.8MB PDF] edited by Douglas A. Vakoch—are not saying these carvings were definitely made by aliens. They're saying that, since we don't really know the origin and meaning of these markings—which were made thousands of years ago all cross Europe, America and India—we can assume that they are made by aliens as a test to what we may encounter when we actually make contact with a civilization from another planet.

It's a serious book—deep and complex, but quite accessible. I have been going through it and it is truly fascinating stuff. And I'm not only talking about the gem at the top of this article:

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