How did oxygen levels in the atmosphere reach current levels?

Explanation:

This occurred due to the evolution of photosynthetic organisms billions of years ago. Remember photosynthetic organisms take up carbon dioxide and evolve out oxygen as a byproduct in photosynthesis. The proliferation of these organisms caused a change in the atmospheric composition by taking out carbon dioxide and increasing oxygen. This event is known as the Great Oxygenation Event. This also caused a reduction in temperatures in the earth’s atmosphere because of carbon dioxide, which is a greenhouse gas, reduced drastically.

scientists have discovered that hiv does not cause aids by the virus's direct effect on the host's immune cells, but rather through the cells' lethal influence on one another. researchers from the gladstone institutes have revealed that hiv does not cause aids by the virus's

one part of the electromagnetic spectrum that arrives on earth as solar radiation from the sun is the visible spectrum. wavelengths of the visible spectrum combine to form what we refer to as

answer - d) ultraviolet radiation.

violet /   380–450 nm / 668–789 thz

violet is number 1 in the chart of visible light.