The fossil records and their appearance in certain periods, but not in others, are suggesting that in the early history of the Earth, the life was not developed, or more specifically, the complex life was not developed.
More complex life started to develop during the Phanerozoic eon, thus the numerous fossils in this eon, but in the period before this eon, there was not complex life, but only very simple life forms, and those are very hard to preserve, thus the fossils are lacking.
