What makes studying the beginnings of plate tectonics difficult?

Answer is B and D are the best answers

According to researchers, this theory is believed to have started 4.6 billion years ago. However much we shed light on theories that took place up to 3 billion years ago, the plate tectonic theory is not suffient enough to explain the earth's and crust formation before 1 to 3 billions years ago through to the earliest formation of planet 4.6 billion years ago. The difference with these numbers are big and it is simply hard to find well-preserved ancient rocks