Q. Which of the following statements is correct regarding Great Oxidation Event?
1) The event was triggered by blue-green algae.
2) The oxidation was triggered first in the ocean.
Select the correct answer using the codes given below

[A] 1 only

[B] 2 only

[C] Both 1 and 2

[D] Neither 1 nor 2

Answer: B

Statement 1 is incorrect. Cyanobacteria possessed the machinery to utilize water as a fuel source by oxidizing it. More significantly, the by-product of photosynthesis happened to be oxygen.

Statement 2 is correct. The levels of oxygen released into the seawater by cyanobacteria gradually increased over time, and over a span of 200-300 million years, oxygen was produced at a faster rate than it could react with other elements or get sequestered by minerals. The oxygen released by cyanobacteria steadily accumulated over vast swathes of the ocean and oxygenated the water. Gradually, the accumulated oxygen started escaping into the atmosphere.