If anyone could work out how much mass (not weight :) ) have humanity added to the Earth, seeing that the LHC (atlas, I believe, weighs 7000 tonnes), and the Three Gorges dam in China slowed the Earth's rotation by 0.06 micrometers. How much does the collective building of humanity added to the mass of the Earth?
All mass used in construction on Earth comes from material on Earth. Since mass is conserved, there is no change. If we start harvesting material from the moon or asteroids for use in construction on Earth, then there would be a net increase in mass. But currently, the net mass of Earth has decreased due to man, since we have launched many satellites into space which came from material on Earth.
Don't confuse redistribution of mass with gain/loss of mass. There's a net loss of hydrogen and helium from the uppermost tenuous atmosphere. This far outweighs the incoming meteorites and miscellaneous space dust - by some 50,000 to 90,000 tonnes per year. Both of these components eclipse, by orders of magnitude, the loss of mass from radioactive decay, satellites that drift into space, recovered moon rocks, and assorted other human activities. The exception to losing mass may be those rare years when large bodies collide with Earth, in which case there will be anomalous net gains in mass.