[blam]

Carolina Bays (500,000 of these along the east coast of US)

[BenLurkin]

Could those be sink holes?

If those are impact craters then the earth got a nasty pelting from some object that broke up and then struck the earth in 500,000 pieces. Would definitely be bad news if it happened today. You probably know that the chain impacts are thought to be the result of impact from a Shoemkaer-Levy type object eg a string of fragments traveling "in-line".