That is some answer here that explains the mystery. I note this in the report. "The Great Unconformity was first described by John Wesley Powell during a boat expedition in 1869 along the Colorado River, which carved Arizona's Grand Canyon. It was one of the first well-documented puzzling geologic features in North America, according to researchers. Peak and her team completed an expedition like Powell's in spring 2021 and were greeted with the same stark boundary between Grand Canyon rock layers, which could be seen from the river. At particular sites along the canyon, 1.4 to 1.8-billion-year-old rocks are found lying beneath much younger 520-million-year-old rocks, according to the researchers."
The answer(s) provided appeal to non-repeatable events in science. I could ask where are the proto-earth rocks that existed before Theia hit the proto-earth and created the Moon? Where is a rock from Theia I can hold today? What ever answers here as to missing rocks not found today, will be non-repeatable events in science.