Fossils are the remains or traces of ancient life which have been preserved by natural causes in the Earth's crust.
(Fossils; are; the remains or traces of ancient life which have been preserved by natural causes in the Earth's crust) (the remains or traces of ancient life; have been preserved; by natural causes in the Earth's crust)
Fossils the remains or traces of ancient life
are have been preserved
the remains or traces of ancient life which have been preserved by natural causes in the Earth's crust
by natural causes in the Earth's crust