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.

primary succession begins with a bare rock and ends with a forest secondary succession begins after a natural disaster where there is a temporary setback after a forest fire or local destruction, but the surrounding area can fill in

there are 35 white marbles

step-by-step explanation:

y- yellow marbles

4y + 5 = 45

subtract 5 from both sides

4y = 40

divide for from both sides

y = 10

plug in 10 to get 40 yellow marbles then subtract by 5 to get 35 marbles

thus there are only 10 yellow marbles