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.
So tomorrow, lets just say, for some incredibly stupid reason, somebody in the US nuclear command center, or whatever the hell it is that launches nuclear weapons, orders the anihilation of Russia. Russia retaliates, yada yada yada, nuclear winter, cockroaches inherit the earth.
Then, lets say, I don't know, 20,000 years from now, an alien civilization visits the earth. What is the first thing they find that lets us know that we were here? I've thought about this for a while, and I think that the first thing that they would probably find, the most obvious thing anyway, are the great pyramids at Gaza. Now, we've certainly built taller structures, but I'm not sure that they would last for 20,000 years, while I'm reasonably certain that the pyarmids would.
So of all the things that humanity has done since, all the wars, all the inventions, all the buildings, all the nations, perhaps, none of these are as memorable as the buildings that were built 4,500 years ago. These aliens might be more interested in ancient Egyptian culture and history than they would be in the current world. Kinda makes you think.
I'm moving into a new apartment soon with Seth and Luke. Its gonna rock, we're gonna have so much fun the first week, then go so annoyed with each other that we'll never speak to one another again.
I wish I could sing like Hank Williams