Oxygen ( ) is
A) a gas which principally originates from volcanic sources.
B) a by-product of photosynthesis.
C) one of the gases from Earth's earliest atmospheres.
D) now measured at 78.084% by volume in the homosphere.

Question

Oxygen (  ) is
A) a gas which principally originates from volcanic sources. 
B) a by-product of photosynthesis. 
C) one of the gases from Earth's earliest atmospheres. 
D) now measured at 78.084% by volume in the homosphere.

Quizplus · Accepted Answer

Oxygen is primarily produced through photosynthesis by plants and algae, which release it into the atmosphere as a by-product. While volcanic activity can release small amounts of oxygen, it is not the primary source. Oxygen was likely not present in Earth's earliest atmosphere composed mainly of nitrogen, methane, and ammonia. However, it has become the most abundant gas in the homosphere, now measuring at 78.084% by volume.

Oxygen ( ) Is