Ozone is a gas in the atmosphere that protects everything living on the Earth from harmful ultraviolet (UV) rays from the Sun. Without the layer of ozone in the atmosphere, it would be very difficult for anything to survive on the surface.
Firstly, it is the only substance on Earth that is in liquid form at the temperatures commonly found on the Surface of our planet. Secondly, it is a superb solvent, meaning that other substances regularly and easily dissolve into it. This allows water to carry nutrients to cells, and carry waste away from them.
Oxygen is what is known as a highly reducing gas: it likes to combine with other molecules like atmospheric gases or surface rocks. ... Before the rise of photosynthesis, a process which produces oxygen and continues to this day to replenish our supply, Earth's atmosphere had no appreciable quantity of oxygen whatsoever.