The early atmosphere of Earth was vastly different from the atmosphere we have today. Earth formed about 4.5 billion years ago, and the atmosphere was likely composed mostly of hydrogen and helium, with trace amounts of other gases such as methane, ammonia, and water vapor. This atmosphere was very thin, and it did not provide any significant protection from the sun's radiation.

Over time, the Earth's atmosphere began to change as the planet's surface cooled and water vapor condensed into oceans. The release of gases from volcanoes and other geological processes also contributed to the changing atmosphere. By about 2.4 billion years ago, the Earth's atmosphere had become more oxygen-rich, and it was able to support the first photosynthetic organisms.

The rise of oxygen in the atmosphere was a major turning point in the Earth's history. Oxygen is essential for life, and it allowed for the evolution of complex organisms. The oxygen-rich atmosphere also helped to protect the Earth from the sun's radiation, allowing the planet to become more habitable.

The Earth's atmosphere has continued to evolve over time, and it has reached the composition that we have today. The atmosphere is now about 78% nitrogen, 21% oxygen, and 1% other gases. This atmosphere provides a suitable environment for life, and it allows us to enjoy the world that we live in.