Scientists have been examining those rocks for more than 20 years now, comparing them to rocks on Earth.
(Scientists; have been examining; those rocks; T:for more than 20 years; T:now) Context(Scientists have been examining,List([0, 30))):(Scientists; have been examining those rocks comparing; them; to rocks on Earth)
Scientists have been examining,List([0, 30))
Scientists Scientists
have been examining have been examining those rocks comparing
those rocks T:for more than 20 years T:now
them to rocks on Earth