Earth\\\'s atmosphere has not always contained enough oxygen to support life. Wh

Question

Earth's atmosphere has not always contained enough oxygen to support life. What was responsible for enriching Earth's atmosphere with oxygen?

A.photosynthesis by early land plants

B.the evolution of land animals

C.an asteroid colliding with Earth

D.photosynthesis by cyanobacteria

What is thought to have contributed to the evolution of aerobic respiration?

A.formation of liquid water on Earth

B.competition with multicellular organisms

C.build-up of oxygen in the atmosphere

D.movement of life onto land

Explanation / Answer

D.photosynthesis by cyanobacteria

Cyanobacteria   was the first organisms on Earth to perform oxygenic photosynthesis. Cyanobacteria eventually released enough oxygen to transform the environment.

C.build-up of oxygen in the atmosphere

The thought to have contributed to the Evolution of aerobic respiration is to build up oxygen in the atmosphere. The aerobic organisms evolve to consume oxygen and bringing about equilibrium in its availability. Because free oxygen is an important constituent of the atmosphere.

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