Why did the presence of cyanobacteria on Earth in the past allow humans to exist?
A) It was the first form of life.
B) It oxygenated the atmosphere.
C) It fertilized the soil to let plants grow.
D) It increased the carbon dioxide in the atmosphere, causing the greenhouse effect.
E) It was the first life form based on DNA.

Question

Quizplus · Accepted Answer

Cyanobacteria were the first organisms to perform oxygenic photosynthesis, which created oxygen as a byproduct. This oxygen accumulated in the atmosphere and eventually led to the oxygenation of the Earth's atmosphere, allowing for the evolution of more complex life forms, including humans.

Why Did the Presence of Cyanobacteria on Earth in the Past