What is the History of the Earths Atmosphere?
Earth has had three atmospheres, each different in chemical composition. The first of Earth’s atmospheres, formed when the planet was still very young, was primarily hydrogen and helium. This atmosphere is about 4.57 years old, and was short-lived – heat from the molten crust and solar wind dissipated this layer. Hydrogen and helium are not heavy enough to make up a stable atmosphere unless the planet is very massive – these elements are more likely to gain escape velocity during random thermal fluctuations. This is part of the reason why hydrogen and helium are very rare in Earth’s atmosphere today. Around 4.4 billion years ago, crust solidified, and numerous volcanoes formed, ejecting steam, carbon dioxide, and ammonia into the skies. Over time, the density of these volcanic gases became sufficient to form a second Earth’s atmosphere, primarily of carbon dioxide and water vapor. Some nitrogen was present, but barely any free oxygen. This is similar to Venus’ present atmosphere, which
Earth has had three atmospheres, each different in chemical composition. The first of Earth’s atmospheres, formed when the planet was still very young, was primarily hydrogen and helium. This atmosphere is about 4.57 years old, and was short-lived — heat from the molten crust and solar wind dissipated this layer. Hydrogen and helium are not heavy enough to make up a stable atmosphere unless the planet is very massive — these elements are more likely to gain escape velocity during random thermal fluctuations. This is part of the reason why hydrogen and helium are very rare in Earth’s atmosphere today. Around 4.4 billion years ago, crust solidified, and numerous volcanoes formed, ejecting steam, carbon dioxide, and ammonia into the skies. Over time, the density of these volcanic gases became sufficient to form a second Earth’s atmosphere, primarily of carbon dioxide and water vapor. Some nitrogen was present, but barely any free oxygen. This is similar to Venus’ present atmosphere,
