I think you use the word rubbish a little too easily Bernardo.
I was working on 500,000,000,000 rather than 100,000,000,000 which give the 16 rather than 3 thousand years.
You might also want to look again at your own maths
100,000,000,000 at 1mm is 100 cubic metres or with my numbers 500 cubic metres
Thats 22 m x 22m at 1 metre deep which is not a large beach but the purpose is to convey a concept not to produce a mathamatically rigorous result.
I think rubbish was a bit strong