What is the qualifying standard to be seeded at the Chicago Marathon?

I've looked on the marathon website and cannot find what the seeding times are. Do these vary from year to year? I've heard you can be seeded by submitting a half marathon time as well. Anyone know?|||For the chicago marathon, all you have to do is sign up. (if seeding means being able to run it) and they take everything down after six hours, thats all i can think of.|||Well, I believe you have to do a full marathon at lease in 6 hours. A couple of years ago I was seeded at the chicago marathon. I had finished the Los Angeles marathon in 6 hours.