In conclusion, concrete is an amazing invention that has made it's mark in history. Everything is made of concrete now. Arguably, it may be the best building material mankind has created. It is strong and malleable to any shape you want it to be. Although it does emit it's fair share of carbon dioxide, the benefit of having long-lasting and sturdy structures definitely outweighs the emissions it produces, rather than having to re-build everything every 20 or so years. Millions of years later, maybe when humans go extinct and aliens come visit - all they will see is a wasteland of concrete. Steel would have long rusted away, wood rotten, every other material would be reduced to nothing. We really are living in a world of concrete.