Fill in the blanks. David is a research scientist who is giving a lecture to a class of students on how life began on Earth. Help him complete the sentences.
Scientists have found (shells, stromatolites, rocks) containing fossilized cyanobacteria (blue-green algae). They show that life has been present on the Earth from early ages. Oparin and Haldane were two scientists who hypothesized that life needed reducing environments initially to appear. The ocean in the early ages was (anoxic, toxic, pyrexic) and acidic.