I don’t understand why the debris layer should be 10 cm thick. That isn’t all debris from the space object, is it? I’m thinking that it would take a huge amount of debris to cover the earth with 10 cm of dust, and that much additional mass would certainly have caused the rotation of the earth to slow.
The debris layer they studied in lakes was 10 cm; the thickness of the layer depended on the distance from the impact, depths iow varied. :’)