the earth first atmosphere formed form
The Earth's first atmosphere formed from the gases that were released during the planet's formation process. This early atmosphere was primarily composed of hydrogen and helium because these light gases were the most common in the nebula from which the Solar System originated. However, Earth's strong gravitational pull was not sufficient to retain these light gases, especially given the intense solar wind from the young Sun, which likely stripped away much of the initial atmosphere.
About 4.5 billion years ago, as the Earth cooled after its formation, volcanic outgassing started to contribute significantly to the atmosphere. This secondary atmosphere was composed of gases released from the planet's interior through volcanic activity, including water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), methane (CH4), ammonia (NH3), and nitrogen (N2).
Over time, as the Earth continued to cool, water vapor condensed into liquid water and fell as rain, filling the basins that became Earth's oceans. The early oceans acted as a sink for carbon dioxide, which helped to moderate the greenhouse effect and stabilize the planet's climate.
The introduction of oxygen (O2) into the atmosphere occurred much later, primarily driven by biological processes. Photosynthetic organisms, such as cyanobacteria, began converting water and carbon dioxide into glucose and free oxygen through photosynthesis around 2.4 to 3 billion years ago, during the Great Oxygenation Event. This dramatically changed the composition of the atmosphere, ultimately leading to the oxygen-rich atmosphere we have today, which supports complex life.