Worthless and Weak

So, after reading some comments about the pyramids, I think my point was misinterpreted, or rather, miscommunicated. In order to signal to aliens who may be surveying the earth in the far future, we would have to build something that has three characteristics. First, it must be noticible. It must be durable, so it will last a long time. Finally, and most importantly, they must be of obvious human design. While the things Mark talked about the other day (dam footprints, radioactivity, strip mines) are plenty of the first two, I'm not entirely sure that aliens would necessarily identify these things as of human design. If an Alien civilization is doing a detailed inspection of the earth any time within the next hundred thousand years, of course they'll find plenty of evidence we were here. But if they are surveying a planet a day, they might not care too much about the geology of planet earth, and skip over the mines.

The great pyramids have all three of these characteristics, they are noticible, (ie big), they are durable, (likely to last for another 20,000 years, at least I believe), and they are obviously of intelligent design (their bases are almost perfectly square, they are about three minutes off true north).

Human civilization started, depending on who you ask, began in about the year 3500 BC, give or take a few hundred years. The great pyramids were built about 2500 BC. So, within one thousand years of human civilization, we built something that has all three characteristics. Had humanity died off two thousand years into its life, there would still have been a lasting monument to our existance.