No one can say for certain, but scientists are studying the fossil clues left in the rocks to try to solve this mystery.
(No one; can say; for certain) (scientists; are studying; the fossil clues left in the rocks) (the fossil clues; left; L:in the rocks; to try to solve this mystery)
No one scientists the fossil clues
can say are studying left
for certain
the fossil clues left in the rocks
L:in the rocks to try to solve this mystery