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 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 (devoid of oxygen) and acidic.

Sample

"Scientists have found 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 (devoid of oxygen) and acidic."

However, the cyanobacteria produced oxygen as a waste product, as cyanobacteria are photosynthetic. This eventually lead to the Great Oxygenation Event, as this nearly killed off the cyanobacteria as a whole. Although, a few plants at this time used oxygen in their own metabolic processes. This allowed these plants to grow and breed faster. This lead to today, where the majority of multi-cellular life on Earth started from these oxygen-sucking plants, not the cyanobacteria.