Simple life forms are believed to have existed on Earth throughout this period but no fossil remains have yet been found in these rocks.
(Simple life forms; are believed; ) (Simple life forms; to have existed; L:on Earth; T:throughout this period) (no fossil remains; have been found; L:in these rocks; T:yet)
Simple life forms Simple life forms no fossil remains
are believed to have existed have been found
L:on Earth T:throughout this period
L:in these rocks T:yet