Poll Results

Total votes: 3050

Less than 5 years: 22 (0.7%)
5-10 years: 78 (2.6%)
10-15 years: 121 (4.0%)
15-20 years: 207 (6.8%)
20-30 years: 309 (10.1%)
30-40 years: 217 (7.1%)
40-50 years: 172 (5.6%)
50-75 years: 287 (9.4%)
75-100 years: 338 (11.1%)
100-200 years: 498 (16.3%)
200-300 years: 81 (2.7%)
300-500 years: 46 (1.5%)
500-750 years: 15 (0.5%)
750-1000 years: 15 (0.5%)
1000-1500 years: 14 (0.5%)
1500-2000 years: 41 (1.3%)
Over 2000 years: 589 (19.3%)

It was really not my intention for people to include things like rocks when they answered this question, but apparently a lot of you are literal enough (littoral enough?) to have thought of that possibility. I may rerun this poll later, specifically restricting it to human-made objects.