According to scientific evidence, earth’s earliest atmosphere lacked oxygen. over time, oxygen was added to the atmosphere. which statements explain how this change occurred and how it affected life on earth? choose all answers that are correct.
a. adding oxygen to earth's atmosphere allowed for the development of eukaryotic organisms, which need oxygen to carry out many of their life processes.

b. oxygen is needed to carry out photosynthesis. when cyanobacteria evolved, they began to carry out photosynthesis.

c. adding oxygen to earth's atmosphere allowed for the development of prokaryotic organisms, which need oxygen to carry out many of their life processes.

d. oxygen is a product of photosynthesis. when cyanobacteria evolved, they began to carry out photosynthesis.

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