It could have been released from the ineterior of the earth through volcanic activity. It could have been deposited by comets and icy particles. Weather refers to the circulation of the Earth's atmosphere. Sunlight heats the Earth and the atmosphere tries to redistribute the heat from warm areas to cool areas. The atmosphere responds to the change heat input of the Sun.
Climate refers to atmospheric changes that occur over decades and centuries.
The beginning and ends of ice ages refer to changes in climate. It appears as though the chemical makeup of the atmosphere has been changed by the presence of life on Earth. The atmosphere of early Earth did not contain free oxygen. It contained abundant amounts of carbon dioxide. Many chemical reactions are possible in this type of environment that could lead to the production of living organisms.