Rare Earth hypothesis the atmosphere is not stripped over time by solar winds. A terrestrial planet of the right size is needed to retain an atmosphere, like Earth and Venus. On Earth, once the giant impact of Theia thinned Earth's atmosphere, other events were needed to make the atmosphere capable of sustaining life. The Late Heavy Bombardment reseeded Earth with water lost after the impact of Theia. The development of an ozone layer formed protection from ultraviolet (UV) sunlight. Nitrogen and carbon dioxide are needed in a correct ratio for life to form. Lightning is needed for nitrogen fixation. The carbon dioxide gas
Snowball Earth with methane in the atmosphere, oxidizing it to carbon dioxide, a much weaker greenhouse gas, and a younger—thus fainter—Sun, which would have emitted 6 percent less radiation in the Neoproterozoic. Normally, as Earth gets colder due to natural climatic fluctuations and changes in incoming solar radiation, the cooling slows these weathering reactions. As a result, less carbon dioxide is removed from the atmosphere and Earth warms as this greenhouse gas accumulates—this 'negative feedback' process limits the magnitude of cooling. During the Cryogenian period, however, Earth's continents were all at tropical latitudes, which made this moderating process less effective, as high