Until 40 years ago, scientists thought that stromatolites - the oldest known evidence of life on Earth - existed purely as fossils, but now they study living forms around the world.
(they; study; living forms around the world; T:now) (scientists; thought; that stromatolites - the oldest known evidence of life on Earth - existed purely as fossils, but now they study living forms around the world; T:Until; T:40 years ago) Context(scientists thought,List([20, 38))):(stromatolites; existed; )
scientists thought,List([20, 38))
they scientists stromatolites
study thought existed
living forms around the world T:now
that stromatolites - the oldest known evidence of life on Earth - existed purely as fossils, but now they study living forms around the world T:Until T:40 years ago