<span>Ozone is simply a molecule consisting of 3 oxygen atoms, which reacts strongly with other molecules. Ozone is created in the stratosphere when high energy uv radiation causes on O2 molecule to split. The free oxygen atoms collide and react with other O2 molecules to form O3.</span>
Production is highest where the solar uv is the greatest eg near the tropics, but once created, the ozone is then circulated towards the poles by the atmosphere. The amount of ozone in the stratosphere can vary with location, season and even day to day climatic conditions.
<span>The process of ozone creation is what makes the O3 in the atmosphere very effective at shielding the Earth from harmful uv radiation, which can cause many biological problems, such as skin cancer. However, due to its high reactivity, the uv found in the tropospher at ground level can aslo be dangerous as a toxic pollutant which is harmful to plants and lung tissue, and is a major cause of smog.</span>
The study pushes back the clock on the origin of Earth's water by hundreds of millions of years, to around 4.6 billion years ago, when all the worlds of the inner solar system were still forming. Scientists had suspected that our planet formed dry, with high-energy impacts creating a molten surface on the infant Earth.
Answer: 4.6 billion years.
Astronomers have seen stars forming within a nebular cloud. As the nebular cloud condenses and its own gravitational attraction collapses it, heat and energy build up creating a planet.
