The upper rocks in the muav limestone are about 505 million years old. the lower rocks in the redwall limestone are about 340 million years old. which could explain this gap? the trilobites became extinct after the bright angel shale period. a. the earth's climate conditions prevented the formation of new limestones during that gap of time. b. either no deposition occurred or it was removed by erosion. c. the rock layers were subducted beneath the crust during that gap in time. d.