Earth and space science.
complete the sentences to explain how photosynthetic organisms changed our lives on earth.
the in the atmosphere that all living beings depend on was generated by cyanobacteria during the archaean and proterozoic eras. the presence of this substance is what makes possible on earth.

1.
a. carbon dioxide
b. oxygen
c. water vapor
d. nitrogen

2.
a. the water cycle
b. visibility
c. photosynthesis
d. combustion

1. Oxygen

2. Combustion

Explanation:

Cyanobacteria are known as the first photosynthetic organism on Earth. They used H2O instead of H2S to fix carbon dioxide into energy-rich molecules such as glucose. The process, therefore, produced a tremendous amount of oxygen (99% of total oxygen), which was then released from oceans to Earth's atmosphere.

We know that oxygen is an oxidizer that helps in burning (combustion). When the oxygen started accumulating in the atmosphere, oxidation of many compounds started occurring, e.g. iron oxidation. Water was already available at that time. Photosynthesis also existed because cyanobacteria produced oxygen through photosynthesis. Thus the presence of oxygen didn't influence photosynthesis. In fact, the presence of oxygen, due to oxidation processes, leads to the formation of complex life processes that we see today. Previously, earth atmosphere was mostly reduced because of very limited availability of other oxidizers.

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