Select the statements about the k-t boundary that are true. select all that apply. select all that apply. the k-t boundary is a thin layer of clay found only in gubbio, italy. the k-t boundary in zumaia, spain is sharp--representing an abrupt change in the marine ecosystem. the k-t boundary separates rock layers of the cretaceous period from those of the tertiary period. the k-t boundary dates to 65 million years ago (when the dinosaurs disappeared).