You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "where does oxygen in earth atmosphere come from?" whose answer is photosynthesis.
Each document should contain about 30 words, and these documents should contain useful information.

Query: origin of atmospheric oxygen
Useful Output:

Doc 1: Using multi-isotope measurements of sulfur these low oxygen levels were estimated to have occurred between about 3.8 and 2.7 billion years ago.
Doc 2: The evolution of O2-producing cyanobacteria that use water as terminal reductant transformed Earth's atmosphere to one suitable.
Doc 3: Photosynthesis as a source of oxygen. It is a generally accepted belief that in the universe there exist only one significant source of free
Doc 4: The breathable air we enjoy today originated from tiny organisms, although the details remain lost in geologic time.
Doc 5: The great oxidation event, which released oxygen into Earth's atmosphere, was catalyzed by cyanobacteria and ultimately led to the evolution