Oxygen may not be the most abundant gas in the atmosphere (that’s nitrogen), but it is certainly the most important one. Without it, no living being can survive. Have you ever wondered what would happen if the whole world was cut off from its oxygen supply for a mere 5 seconds? You might think that holding your breath for 5 seconds isn’t a very big deal. In reality, however, if the whole world was deprived of it for that long, the results would be catastrophic. Some debilitating changes would occur if that Oxygen lost: The sky during the day would get dark Light from the Sun reaches the Earth’s surface as a result of multiple reflections that occur when light particles bounce off the particles in the air (dust, oxygen molecules, other impurities in the air). The absence of oxygen means less particles for the light to bounce on, so the sky would appear dark, almost black, actually. Essentially, light would reach the Earth, but it would seem as if though it were being emitted from a point source, as opposed to what we normally see (the rays of the Sun spread in every direction).